0.5wisediskcleaner

TheCMSHighLevelTriggerTheCMSTriggerandDataAcquisitionGroup1Abstract.
AttheLargeHadronCollideratCERNtheprotonbunchescrossatarateof40MHz.
AttheCompactMuonSolenoidexperimenttheoriginalcollisionrateisreducedbyafactorofO(1000)usingaLevel-1hardwaretrigger.
AsubsequentfactorofO(1000)datareductionisobtainedbyasoftware-implementedHighLevelTrigger(HLT)selectionthatisexecutedonamulti-processorfarm.
InthisreviewwepresentindetailprototypeCMSHLTphysicsselectionalgorithms,expectedtriggerratesandtriggerperformanceintermsofbothphysicseciencyandtiming.
PACSnumbers:13.
85.
-t,07.
05.
Kf,07.
05.
Tp,02.
07.
UuacceptedbyEPJ,Nov.
2005(page2)TheparticipantsintheCMSTriggerandDataAcquisitionGroupandthecontributorstotheHighLevelTriggerbyCountryandInstitute.
CorrespondancetoM.
Spiropulu,CERN-PH,1211Geneva23,Switzerland;smaria@cern.
chCMSHighLevelTrigger2TheCMSTriggerandDataAcquisitionGroup2Institutf¨urHochenergiephysikderOeAW,Wien,AUSTRIAW.
Adam,T.
Bergauer,C.
Deldicque,J.
Er¨o,R.
Fruehwirth,M.
Jeitler,K.
Kastner,S.
Kostner,N.
Neumeister**1a,2,M.
PadrtaP.
Porth,H.
Rohringer,H.
Sakulin**1b,J.
Strauss,A.
Taurok,G.
Walzel,C.
-E.
WulzVrijeUniversiteitBrussel,Brussel,BELGIUMS.
Lowette,B.
VanDeVyver**1aUniversiteLibredeBruxelles,Bruxelles,BELGIUMG.
DeLentdecker,P.
VanlaerUniversiteCatholiquedeLouvain,Louvain-la-Neuve,BELGIUMC.
Delaere,V.
Lemaitre,A.
Ninane,O.
VanderAaInstituteforNuclearResearchandNuclearEnergy,Soa,BULGARIAJ.
DamgovHelsinkiInstituteofPhysics,Helsinki,FINLANDV.
Karim¨aki,R.
Kinnunen,T.
Lampen,K.
Lassila-Perini,S.
Lehti,J.
Nysten,J.
TuominiemiLaboratoireLeprince-Ringuet,EcolePolytechnique,IN2P3-CNRS,Palaiseau,FRANCEP.
BussonInstitutdeRecherchesSubatomiques,IN2P3-CNRS-ULP,LEPSIStrasbourg,UHAMulhouse,Strasbourg,FRANCET.
Todorov**1bRWTH,I.
PhysikalischesInstitut,Aachen,GERMANYG.
SchweringInstitutf¨urExperimentelleKernphysik,Karlsruhe,GERMANYP.
Gras**3UniversityofAthens,Athens,GREECEG.
Daskalakis**4,A.
SfyrlaInstituteofNuclearPhysics"Demokritos",Attiki,GREECEM.
Barone,T.
Geralis,C.
Markou,K.
ZachariadouKFKIResearchInstituteforParticleandNuclearPhysics,Budapest,HUNGARYP.
HidasTataInstituteofFundamentalResearch-EHEP,Mumbai,INDIAS.
Banerjee**1c,K.
Mazumdar**1aTataInstituteofFundamentalResearch-HECR,Mumbai,INDIAS.
BanerjeeUniversit`adiBari,PolitecnicodiBarieSezionedell'INFN,Bari,ITALYM.
Abbrescia,A.
Colaleo**1a,N.
D'Amato,N.
DeFilippis,D.
Giordano,F.
Loddo,M.
Maggi,L.
Silvestris,G.
ZitoCERN/LHCC02-26p.
465CMSHighLevelTrigger3Universit`adiBolognaeSezionedell'INFN,Bologna,ITALYS.
Arcelli,D.
Bonacorsi,P.
Capiluppi,G.
M.
Dallavalle,A.
Fanfani,C.
Grandi,S.
Marcellini,A.
Montanari,F.
Odorici,R.
TravagliniUniversit`adiCataniaeSezionedell'INFN,Catania,ITALYS.
Costa,A.
TricomiUniversit`adiFirenzeeSezionedell'INFN,Firenze,ITALYV.
Ciulli,N.
Magini,R.
RanieriLaboratoriNazionalidiLegnarodell'INFN,Legnaro,ITALY(associatedinstitute)L.
Berti,M.
Biasotto,M.
Gulmini**1a,G.
Maron,N.
Toniolo,L.
ZangrandoUniversit`adiPadovaeSezionedell'INFN,Padova,ITALYM.
Bellato,U.
Gasparini,S.
Lacaprara,A.
Parenti,MPassaseoP.
Ronchese,S.
Vanini,S.
VenturaP.
L.
ZottoUniversit`adiPerugiaeSezionedell'INFN,Perugia,ITALYD.
Benedetti,MBiasini,L.
Fan`o,L.
ServoliUniversit`adiPisa,ScuolaNormaleSuperioreeSezionedell'INFN,Pisa,ITALYG.
Bagliesi,T.
Boccali,S.
Dutta,S.
Gennai,A.
Giassi,F.
Palla,G.
Segneri,A.
Starodumov**5,6,R.
TenchiniUniversit`adiRomaIeSezionedell'INFN,Roma,ITALYP.
Meridiani,G.
OrgantiniUniversit`adiTorinoeSezionedell'INFN,Torino,ITALYN.
Amapane,F.
Bertolino,R.
CirioChonnamNationalUniversity,Kwangju,KOREAJ.
Y.
KimI.
T.
LimDongshinUniversity,Naju,KOREAM.
Y.
PacSeoulNationalUniversity,Seoul,KOREAK.
K.
Joo,S.
B.
KimSungkyunkwanUniversity,Suwon,KOREAY.
I.
Choi,I.
T.
YuKyungpookNationalUniversity,Taegu,KOREAK.
Cho,J.
Chung,S.
W.
Ham,D.
H.
Kim,G.
N.
Kim,W.
Kim,J.
CKim,S.
K.
Oh,H.
Park,S.
R.
Ro,D.
C.
Son,J.
S.
SuhNationalCentreforPhysics,Quaid-I-AzamUniversity,Islamabad,PAKISTANZ.
Aftab,H.
Hoorani,A.
Osman**1aInstituteofExperimentalPhysics,Warsaw,POLANDK.
Bunkowski,M.
Cwiok,W.
Dominik,K.
Doroba,M.
Kazana,J.
Krolikowski,I.
Kudla,M.
Pietrusinski,K.
Pozniak**7,W.
Zabolotny**7,J.
Zalipska,P.
ZychSoltanInstituteforNuclearStudies,Warsaw,POLANDL.
Goscilo,M.
Gorski,G.
Wrochna,P.
ZalewskiCMSHighLevelTrigger4LaboratoriodeInstrumentacaoeFsicaExperimentaldePartculas,Lisboa,PORTUGALR.
Alemany-Fernandez,C.
Almeida,N.
Almeida,J.
C.
DaSilva,M.
Santos,I.
Teixeira,J.
P.
Teixeira,J.
Varela**1a,N.
VazCardosoJointInstituteforNuclearResearch,Dubna,RUSSIAV.
Konoplyanikov,A.
UrkinbaevInstituteforNuclearResearch,Moscow,RUSSIAA.
Toropin**8InstituteforTheoreticalandExperimentalPhysics,Moscow,RUSSIAV.
Gavrilov,V.
Kolosov,A.
Krokhotin,A.
Oulianov,N.
StepanovMoscowStateUniversity,Moscow,RUSSIAO.
L.
Kodolova**1a,I.
VardanyanVincaInstituteofNuclearSciences,Belgrade,SERBIAJ.
Ilic,G.
SkoroUniversidadAutonomadeMadrid,Madrid,SPAINC.
Albajar,J.
F.
deTroconizInstitutodeFsicadeCantabria(IFCA),CSIC-UniversidaddeCantabria,Santander,SPAINA.
Calderon,M.
A.
LopezVirto,R.
Marco,C.
MartinezRivero,F.
Matorras,I.
VilaUniversittBasel,Basel,SWITZERLANDS.
Cucciarelli**1b,M.
KoneckiCERN,EuropeanOrganizationforNuclearResearch,Geneva,SWITZERLANDS.
Ashby,D.
Barney,P.
Bartalini**9,R.
Benetta,V.
Brigljevic**10,G.
Bruno**11,E.
Cano,S.
Cittolin,M.
DellaNegra,A.
DeRoeck,P.
Favre,A.
Frey,W.
Funk,D.
Futyan,D.
Gigi,F.
Glege,J.
Gutleber,M.
Hansen,V.
Innocente,C.
Jacobs,W.
Jank,M.
Kozlovszky,H.
Larsen,M.
Lenzi,I.
Magrans,M.
Mannelli,F.
Meijers,E.
Meschi,L.
Mirabito,S.
J.
Murray,A.
Oh,L.
Orsini,C.
PalomaresEspiga,L.
Pollet,A.
Racz,S.
Reynaud,D.
Samyn,P.
Schar-Hansen,C.
Schwick,G.
Sguazzoni,N.
Sinanis,P.
Sphicas**12,M.
Spiropulu,A.
Strandlie,B.
G.
Taylor,I.
VanVulpen,J.
P.
Wellisch,M.
WinklerPaulScherrerInstitut,Villigen,SWITZERLANDD.
KotlinskiUniversit¨atZ¨urich,Z¨urich,SWITZERLANDK.
Prokoev,T.
SpeerCukurovaUniversity,Adana,TURKEYI.
DumanogluUniversityofBristol,Bristol,UNITEDKINGDOMD.
S.
Bailey,J.
J.
Brooke,D.
Cussans,G.
P.
Heath,D.
Machin,S.
J.
Nash,D.
M.
Newbold,M.
G.
ProbertRutherfordAppletonLaboratory,Didcot,UNITEDKINGDOMJ.
A.
Coughlan,R.
Halsall,W.
J.
Haynes,I.
R.
TomalinCMSHighLevelTrigger5ImperialCollege,UniversityofLondon,London,UNITEDKINGDOMN.
Marinelli**13,A.
Nikitenko**6,S.
Rutherford,C.
Seez**1aBrunelUniversity,Uxbridge,UNITEDKINGDOMO.
SharifBostonUniversity,Boston,Massachusetts,USAG.
Antchev**14,E.
Hazen,J.
Rohlf,S.
WuUniversityofCalifornia,Davis,Davis,California,USAR.
Breedon,P.
T.
Cox,P.
Murray,M.
TripathiUniversityofCalifornia,LosAngeles,LosAngeles,California,USAR.
Cousins,S.
Erhan,J.
Hauser,P.
Kreuzer**13,M.
Lindgren,J.
Mumford,P.
Schlein,Y.
Shi,B.
Tannenbaum,V.
Valuev,M.
VonDerMey**15UniversityofCalifornia,Riverside,Riverside,California,USAI.
Andreeva**1a,R.
Clare,S.
VillaUniversityofCalifornia,SanDiego,LaJolla,California,USAS.
Bhattacharya,J.
G.
Branson,I.
Fisk,J.
Letts,M.
Mojaver,H.
P.
Paar,E.
TrepagnierCaliforniaInstituteofTechnology,Pasadena,California,USAV.
Litvine,S.
Shevchenko,S.
Singh,R.
WilkinsonFermiNationalAcceleratorLaboratory,Batavia,Illinois,USAS.
Aziz,M.
Bowden,J.
E.
Elias,G.
Graham,D.
Green,M.
Litmaath,S.
Los,V.
O'Dell,N.
Ratnikova,I.
Suzuki,H.
WenzelUniversityofFlorida,Gainesville,Florida,USAD.
Acosta,D.
Bourilkov**24,A.
Korytov,A.
Madorsky,G.
Mitselmakher,J.
L.
Rodriguez,B.
ScurlockUniversityofMaryland,CollegePark,Maryland,USAS.
Abdullin**6,15,D.
Baden,S.
C.
Eno,T.
Grassi,S.
KunoriMassachusettsInstituteofTechnology,Cambridge,Massachusetts,USAS.
Pavlon,K.
Sumorok,S.
TetherUniversityofMississippi,University,Mississippi,USAL.
M.
Cremaldi,D.
Sanders,D.
SummersNortheasternUniversity,Boston,Massachusetts,USAI.
Osborne,L.
Taylor,L.
TuuraPrincetonUniversity,Princeton,NewJersey,USAW.
C.
Fisher**15,J.
Mans**16,D.
Stickland,C.
Tully,T.
Wildish,S.
WynhoRiceUniversity,Houston,Texas,USAB.
P.
PadleyUniversityofWisconsin,Madison,Wisconsin,USAP.
Chumney,S.
Dasu,W.
H.
SmithCMSHighLevelTrigger6**1a:AlsoatCERN,EuropeanOrganizationforNuclearResearch,Geneva,SWITZERLAND**1b:NowatCERN,EuropeanOrganizationforNuclearResearch,Geneva,SWITZERLAND**1c:NowalsoatCERN,EuropeanOrganizationforNuclearResearch,Geneva,SWITZERLAND**2:NowatPurdueUniversity,WestLafayette,USA**3:NowatDAPNIA,Centred'EtudesdeSaclay(CEA-Saclay),FRANCE**4:NowatImperialCollege,UniversityofLondon,London,UNITEDKINGDOM**5:NowatInstitutf¨urTeilchenphysik,Eidgen¨ossischeTechnischeHochschule(ETH),Z¨urich,SWITZERLAND**6:AlsoatInstituteforTheoreticalandExperimentalPhysics,Moscow,RUSSIA**7:AlsoatInstituteofElectronicSystems,TechnicalUniversityofWarsaw,POLAND**8:AlsoatUniversit`adiPisa,ScuolaNormaleSuperioreeSezionedell'INFN,Pisa,ITALY**9:NowatUniversityofFlorida,Gainesville,Florida,USA**10:NowalsoatInstituteRudjerBoskovic,Zagreb,CROATIA**11:NowatUniversiteCatholiquedeLouvain,Louvain-la-Neuve,BELGIUM**12:AlsoatMIT,Cambridge,USAandUniversityofAthens,Athens,GREECE**13:NowatUniversityofAthens,Athens,GREECE**14:AlsoatInstituteforNuclearResearchandNuclearEnergy,Soa,BULGARIA**15:NowatFermiNationalAcceleratorLaboratory,Batavia,Illinois,USA**16:NowatUniversityofMinnesota,Minneapolis,Minnesota,USACMSHighLevelTrigger71.
IntroductionTheLargeHadronCollider(LHC)[1],isahadron-hadroncollidertobeinstalledintheLargeElectronPositron(LEP)tunnelattheCERNLaboratory(theEuropeanLaboratoryforParticlePhysicsoutsideGeneva,Switzerland).
Itwillbeauniquetoolforfundamentalphysicsresearchandthehighestenergyacceleratorintheworldformanyyearsfollowingitscompletion.
TheLHCwillprovidetwoprotonbeams,circulatinginoppositedirections,atanenergyof7TeVeach(center-of-mass√s=14TeV).
Thesebeamsuponcollisionwillproduceaneventrateabout1,000timeshigherthanthatpresentlyachievedattheTevatronppcollider[2].
Inordertosupportthe7TeVprotonbeams,intotal11048.
4Teslasuperconductingdipolesand736quadrupoleswillbeinstalledintheundergroundtunnelof26.
6kmcircumferenceformerlyusedbyLEP.
ThephysicspotentialoftheLHCisunprecedented:itwillallowtostudydirectlyandindetailtheTeVscaleregion.
TheLHCisexpectedtoelucidatetheelectroweaksymmetrybreakingmechanism(EWSB)andprovideevidenceofphysicsbeyondthestandardmodel[3].
TheLHCwillbealsoastandardmodelprecisionmeasurementsinstrument[4]mainlyduetotheveryhigheventratesasshownintable1.
Table1.
ApproximateeventratesofsomephysicsprocessesattheLHCforaluminosityofL=2*1033cm2s1.
Forthistable,oneyearisequivalentto20fb1.
ProcessEvents/sEvents/yearW→eν404·108Z→ee44·107tt1.
61.
6·107bb1061013gg(m=1TeV)0.
0022·104Higgs(m=120GeV)0.
088·105Higgs(m=800GeV)0.
001104QCDjetspT>200GeV102109Theprotonbeamscrossatinteractionpointsalongtheringwheredetectorsthatmeasuretheparticlesproducedinthecollisionsareinstalled.
Interaction"Point5"hoststhemultiplepurpose4πcoverageCMSdetector,showningure1.
TheCMSdetectormeasuresroughly22metersinlength,15metersindiameter,and12,500metrictonsinweight.
Itscentralfeatureisahuge,higheld(4Tesla)solenoid,13metersinlength,and6metersindiameter.
Its"compact"designislargeenoughtocontaintheelectromagneticandhadroncalorimetrysurroundingatrackingsystem,andallowsasuperbmuondetectionsystem.
AllsubsystemsofCMSareboundbymeansofthedataacquisitionandtriggersystem.
IntheCMScoordinatesystemtheorigincoincideswiththenominalcollisionpointatCMSHighLevelTrigger8thegeometricalcenterofthedetector.
Thezdirectionisgivenbythebeamaxis.
Therestframeofthehardcollisionisgenerallyboostedrelativetothelabframealongthebeamdirection,θisthepolaranglewithrespecttothezaxisandφtheazimuthalanglewithrespecttotheLHCplane.
Thedetectorsolidanglesegmentationisdesignedtobeinvariantunderboostsalongthezdirection.
Thepseudorapidityη,isrelatedtothepolarangleθanddenedasη≡ln(tan(θ/2)).
Thetransversemomentumcomponentz-axisisgivenbypT=psinθandsimilarlyET=Esinθisthetransverseenergyofaphysicsobject.
Theexperimentcomprisesatracker,acentralcalorimeterbarrelpartfor|η|≤1.
5,andendcapsonbothsides,andmuondetectors.
Thetrackingsystemismadeofseverallayersofsiliconpixelandsiliconstripdetectorsandcoverstheregion|η|10GeV/cinthebarrel.
Bycontrast,whenlookingforsmalldepositsofenergyinindividualclusters,forexamplewhenmakingacalorimetricisolationcut,thebasicclustersoftheIslandalgorithmareCMSHighLevelTrigger17moreappropriateobjectstoworkwith.
Furtherdetailsontheclusteringalgorithmscanbefoundinreference[13].
3.
2.
EndcapReconstructionwiththePreshowerMuchoftheendcapiscoveredbyapreshowerdetectorwithtwoplanesofsiliconstripreadout.
Theenergydepositedinthepreshowerdetector(whichisabout3X0thick)needstobeaddedtothecrystalclusters[14].
TheenergyinthecrystalsisclusteredusingtheIslandalgorithmandtheclustersareassociatedtoformsuper-clusters.
Apreshowerclusterisconstructedineachplane,infrontofeachcrystalclusterofthesuper-cluster.
Thesearchareainthepreshoweriscenteredonthepointdeterminedbyextrapolatingthecrystalclusterpositiontothepreshowerplaneinthedirectionofthenominalvertexposition.
3.
3.
EnergyandPositionMeasurement3.
3.
1.
PositionMeasurementUsingLog-weightingTechniqueAsimplemeasurementoftheshowerpositioncanbeobtainedbycalculatingtheenergy-weightedmeanpositionofthecrystalsinthecluster.
Twofeaturesneedtobeaddressedinmoredetailinordertoobtainaprecisepositionmeasurement.
Therstistheprecisedenitionofthe"crystalposition".
Thelateralpositionofthecrystaldependsupondepthbecausethecrystalsare"o-pointing"andtheincidentparticleandshowerdirectionisnotexactlyparalleltothecrystalaxis.
Thelateralpositionofthecrystalisthusdenedasthe(η,φ)positionofitsaxisataparticulardepth.
Thedepthatwhichtheshowermaximumoccursistakenasthelongitudinalbaricentreoftheshowerwhichhasalogarithmicdependenceontheshowerenergy.
Thisdepthisroughlythelongitudinalcenterofgravityoftheshower,anditsoptimalmeanvaluevarieslogarithmicallywiththeshowerenergy.
Thereisalsoadependenceonparticletype:electronshowershaveamaximumaboutoneradiationlengthlessdeepthanphotonshowers.
InthepositionmeasurementusedforbothIslandandHybridsuper-clustersthedepthismeasuredfromthefrontfaceofthecrystalsalongthedirectionfromthenominalvertexpositiontotheapproximateshowerpositioncalculatedusingthearithmeticenergyweightedmeanoftheshowerfrontfacecenters.
Theenergydependenceisaccountedforwithalogarithmicparametrization[13].
Thesecondfeaturethatrequiresmoredetailedtreatmentisrelatedtothelateralshowershape.
Sincetheenergydensitydoesnotfallawaylinearlywithdistancefromtheshoweraxis,butratherexponentially,asimpleenergyweightedmeanofcrystalenergiesisdistortedandthemeasuredpositionisbiasedtowardsthecenterofthecrystalcontainingthelargestenergydeposit.
Asimplealgorithm,whichyieldsadequateprecisionconsistsofusingtheweightedmean,calculatedusingthelogarithmofthecrystalenergy:x=xi·WiWiCMSHighLevelTrigger18withthesumoverallcrystalsofthecluster,andwherexiisthepositionofcrystali,andWiisthelogweightofthecrystal–thelogarithmofthefractionoftheclusterenergycontainedinthecrystal,calculatedwiththeformula:Wi=W0+lnEiEjwheretheweightisconstrainedtobepositive,orisotherwisesettozero.
W0thencontrolsthesmallestfractionalenergythatacrystalcanhaveandstillcontributetothepositionmeasurement[13].
Sofarwhathasbeendescribedreferstothemeasurementofthepositionofasinglecluster.
Thepositionofasuper-clusteriscalculatedbymakingtheenergy-weightedmeanofthepositionsofitscomponentclusters.
Foranelectronthathasradiatedintothematerial,thismethodallowstoreconstructitspositionatproduction.
3.
3.
2.
EnergyMeasurementandCorrectionsThemeasurementofenergyinthecrystalsisobtainedbysimpleadditionofthedepositsmeasuredinthecrystals–althoughmorecomplexestimatorshavebeenproposed[15].
Evenintheareasnotcoveredbythepreshowerdetectortheenergycontainmentoftheclusteredcrystalsisnotcomplete.
Thereconstructedoverthegeneratorlevelenergydistribution,Emeas/Etrue,showsapeakatafewpercentlessthanunity,andalongtailonthelowsideduetonon-recoveredbremsstrahlungenergy.
TheGaussianpartofthedistributioncorresponds,roughly,totheenergythatwouldbereconstructedfromanelectronintheabsenceofbremsstrahlung.
Theamountoftrackermaterialvariesstronglywithη,asshowningure3,andthussodoestheamountofbremsstrahlungradiation,soavariationinthefractionofeventsinthetailasafunctionofηisexpected.
Thisinevitablyleadstoasmallvariationinthepeakpositionasafunctionofη.
Theenergyscaleis"calibrated"usingcorrectionsdesignedtoplacethepeakinEmeas/Etrueat1.
0,seegure4.
Thecorrectionsareparametrizedintermsofthenumberofcrystalsinthecluster(f(Ncry)corrections).
ThishelpstominimizetheresidualdependenceonbothEandηoftheenergyscale.
Figure5shows,asanexample,Emeas/EtrueasafunctionofthenumberofcrystalsinareconstructedHybridsuper-cluster,forelectronswith101CMSHighLevelTrigger270.
60.
650.
70.
750.
80.
850.
90.
9511.
0500.
20.
40.
60.
811.
2εpxlisol(QCD)εpxlisol(W→eν)Rcone=0.
2Rcone=0.
3Rcone=0.
4Rcone=0.
5L=1034cm-2s-1Figure11.
RejectionagainstjetbackgroundversustheeciencyforelectronsfromWswhenapixel-trackisolationcutisappliedaftertheLevel-2.
5selectionatL=1034cm2s1.
Rconeistheconeradius.
Thepointsrepresentdierentvaluesoftheisolation(seetext).
Table5.
PhotonstreamthresholdsandratesbeforeadditionalLevel-3cuts.
ThresholdRateRate(2*1033cm2s1)(1034cm2s1)SinglephotonET>80GeV(2*1033cm2s1)7HzET>100GeV(1034cm2s1)10HzDoublephotonsET1>35,ET2>20GeV85Hz382HzGeV/cfoundwithinconesofdierentsizes.
3.
6.
2.
PhotonsFurtherETthresholds,higherthanthoseappliedatLevel-2.
0,areappliedtosuper-clustersofsingleanddoubletriggersthatfailtheLevel-2.
5pixelmatching.
Theeventspassingthesecutsformthephotonstream.
Thedi-photonthresholdsareasymmetric,chosentobe5GeVlowerthantheoineanalysiscutsenvisagedfortheStandardModelH→γγsearch[16].
Thesinglephotonthresholdsarechosentogiveanacceptablerate.
Table5liststhethresholdsandtheratesbeforefurtherLevel-3selection.
Backgroundscanberejectedusingtrackisolationcutsandbyrejectingπ0'sbasedontheCMSHighLevelTrigger28Table6.
ElectronandphotonratesoutputbytheHLTatlowandhighluminosity.
(1)π±/π0overlap;(2)π0conversions2*1033cm2s11034cm2s1SignalBackgroundTotalSignalBackgroundTotalSingleelectronW→eν:10Hz(1):5Hz33HzW→eν:35Hz(1):15Hz75Hz(2):10Hz(2):19Hzb/c→e:8Hzb/c→e:6HzDoubleelectronZ→ee:1Hz01HzZ→ee:4Hz04HzSinglephoton2Hz2Hz4Hz4Hz3Hz7HzDoublephoton05Hz5Hz08Hz8HzTOTAL:43Hz94Hzlateralshowershape.
DeningthelongitudinalcoordinateofthevertexisasignicantissuefortheanalysisoftheH→γγsignalchannel.
Foreventswhereoneormoreofthephotonshasconvertedinthetracker,thetracksegmentandtheECALclustercanbeusedtolocatethevertex.
Theverticesintheremainingeventscanbefoundusingalgorithmsthatchoosethetrackvertexassociatedwiththelargesttrackactivity.
TheeciencyforH→γγis80-90%forajetrejectionfactorof30-60inthehighluminosityenvironment.
3.
7.
SummaryofElectronandPhotonHLTSelection3.
7.
1.
FinalRatestoPermanentStorageTheelectronandphotonratesoutputbytheHLTatbothlowandhighluminosity,brokendownbycontribution,arelistedintable6.
Forthelow-luminosityselectionaloosecalorimetricisolationhasbeenappliedtothephotonstreams(ECALETinaconeofradius0.
45,excludingthesupercluster,lessthan3.
5GeV),butnoisolationbeyondthatoftheLevel-1triggerhasbeenappliedtotheelectronstreams.
Tocontrolthetwo-photonratethethresholdshavebeenraisedtoET1>40GeV,ET2>25GeV(equaltothenaloinecutsenvisagedforH→γγ).
Thisreducestheratefrom11Hzto5Hz,andhasanegligibleeectontheeciency,asisshowninthesecondcolumnintable7.
Afullyoptimizedselectionwillalsoinvolvetrackisolationonthephotonstreams(whollyorpartlyreplacingthecalorimetricisolationandtheraisedthreshold)andtrackisolationinthesingleelectronstream.
Thiscanreducethetotalratetoabout26Hz,ofwhichonlyhalfisbackground,withtheintroductionofonlyasmallfurtherineciency.
Forthehigh-luminosityselection,pixel-trackisolationhasbeenappliedtotheelectronstream,andfulltrackisolationhasbeenappliedtothephotonstreams(notrackwithpT>2GeV/cinaconeofR=0.
2).
3.
7.
2.
SignalEcienciesforElectronandPhotonHLTThestreamswheremostworkisrequiredtocontrolthebackgroundratesarethesingle-electronanddouble-photonstreams,so,theecienciesforthedecaysW→eνandH→γγareusedasCMSHighLevelTrigger29Table7.
EciencyforH→γγ(MH=115GeV/c2)throughthecompleteselectionchain,atL=2*1033cm2s1.
BothphotonsinducialregionPhotonspassingoinepTcutsLevel-190.
8%92.
3%Level-298.
7%99.
4%Level-2.
593.
4%99.
1%Level-392%92%Overall(Level-1*HLT)77%83.
7%Table8.
EciencyforelectronsfromWdecaythroughthecompleteselectionchain2*1033cm2s11034cm2s1FiducialFiducialAllducialelectronswithAllducialelectronswithelectronspT>29GeV/celectronspT>34GeV/cLevel-163.
2%87.
2%51.
1%83.
2%Level-288.
8%99.
4%82.
9%99.
3%Level-2.
593.
1%94.
6%92.
8%94.
1%Level-381%82%77%78%HLT(Level-2toLevel-3)67%77%59%73%benchmarks.
Table8liststheeciencyforsingleelectronsfromWdecaythroughthecompleteselectionchain,atL=2*1033cm2s1andatL=1034cm2s1.
EventsarepreselectedrequiringthegeneratedelectronstobewithintheECALducialregionof|η|40GeV,ET2>25GeV.
3.
7.
3.
CPUUsageforElectronandPhotonHLTTable9showstheCPUusageoftheHLTselection,benchmarkedon1GHzprocessor,forjetbackgroundeventsatlowCMSHighLevelTrigger30Table9.
CPUusageoftheHLTelectronselectionforjetbackgroundeventsatL=2*1033cm2s1,benchmarkedon1GHzprocessors.
HLTlevelMeanCPUtime(ms)Level-2.
0154/Level-1eventLevel-2.
532/Level-2eventLevel-3100/Level-2.
5eventTotal162ms/Level-1eventluminosity.
AthighluminositythetimetakenfortheunoptimizedglobalsearchforECALclustersatLevel-2.
0isgreatlyincreasedandtheoveralltotalCPUtimeperLevel-1event,ataluminosityofL=1034cm2s1isaboutthreetimesaslarge,asatL=2*1033cm2s1.
Preliminaryresultsindicatethatthisclusteringtimecanbereducedbyafactor10usingregionalreconstruction.
4.
MuonIdenticationThemuonselectionfortheHLTproceedsintwosteps:rstly,muonsarereconstructedinthemuonchambers,whichconrmstheLevel-1decisionandrenesthepTmeasurementusingmorepreciseinformation;secondly,themuontrajectoriesareextendedintothetracker,whichfurtherrenesthepTmeasurement.
Aftereachstep,isolationisappliedtothemuoncandidates–thecalorimeterbeingusedaftertherststepandthetrackerafterthesecond.
ThemuontrackreconstructionalgorithmusedbytheHLTisseededbythe–uptofour–muoncandidatesfoundbytheLevel-1GlobalMuonTrigger(seeAppendix),includingthosecandidatesthatdidnotnecessarilyleadtoaLevel-1triggeracceptbytheGlobalTrigger.
Thealgorithmusesthereconstructedhitsbuiltfromthedigitizedsignalsinthemuonsystem,andconstructstracksaccordingtotheKalmanltertechnique[18].
TheresultingtrajectoriesareusedtovalidatetheLevel-1decisionaswellastorenethemuonmeasurementinthisLevel-2muonselection.
ThebasisoftheLevel-3muonselectionistoaddsilicontrackerhitstothemuontrajectory,thusgreatlyimprovingthemuonmomentummeasurementandsharpeningthetriggerthreshold.
Isolationcriteriacanbeappliedtothemuoncandidatestoprovideadditionalrejection:atLevel-2usingthecalorimetricenergysuminaconearoundthemuon,andatLevel-3usingthenumberofpixeltracksinaregionaroundtheprojectedmuontrajectory.
Thissuppressesmuonsfromb,c,π,andKdecays.
4.
1.
MuonReconstruction4.
1.
1.
MuonStandaloneReconstructionandLevel-2SelectionReconstructedtracksegmentsfromthemuonchambersareusedformuonidenticationandselectionatCMSHighLevelTrigger31-1-0.
500.
51020040060080010001200(a)-1-0.
500.
51050100150200250300350400(b)-1-0.
500.
510100200300400500600700800(c)Figure12.
Distributionof(1/pTrec-1/pTgen)/(1/pTgen),wherepTgenandpTrecarethegeneratedandLevel-2reconstructedtransversemomentarespectively,showninthreepseudorapidityintervals:a)|η|10GeV/candnopileup.
CMSHighLevelTrigger33-0.
1-0.
0500.
050.
102004006008001000(a)-0.
1-0.
0500.
050.
1050100150200250300350400(b)-0.
1-0.
0500.
050.
10100200300400500600700800(c)Figure13.
Distributionof(1/precT-1/pgenT)/(1/pgenT)wherepgenTandprecTarethegeneratedandLevel-3reconstructedtransversemomenta,respectively,showninthreepseudorapidityintervals:a)|η|22GeV/cathighluminosity,asafunctionofthepseudorapidityofthemuon.
Theeciencyforreferencebackgroundmuonsversustheeciencyforreferencesignalmuonsisshowningure17atlowluminositywithpgenT>16GeV/candathighluminositywithpgenT>22GeV/c.
Thebackgroundrejectioncanbeadjustedbychoosingdierentecienciesforthereferencesignal.
4.
2.
MuonHLTSelectionHerewedescribeaprototypeinclusivemuontriggerbasedonthereconstructionandisolationtoolsdiscussedintheprevioussectionstodemonstratetheperformanceinthemuonHLT.
4.
2.
1.
Single-muonHLTSelectionAsinglemuoninclusivetriggerisformedfromthefollowingrequirements.
AtLevel-1,lowqualityCSCtracksmustbematchedwithRPCtracksbytheGlobalMuonTriggerinordertoensureawell-measuredpT.
Lowqualityheremeansthattherearenostrongrequirementsonthenumberofmuonchambersused,oronwhichofchambersintheregioncrossedbythemuonareused,toidentifythemuon.
AtLevel-2,amuonmustbereconstructedinthemuonsystemandhaveavalidextrapolationtothecollisionvertex.
Inthebarrelregion,atleastoneDT(DriftTube)CMSHighLevelTrigger37Pseudorapidity00.
511.
52Efficiency00.
10.
20.
30.
4L2CalorimeterIsolationL3PixelIsolationL3TrackerIsolation)>22GeVgen(Tp(a)(b)pgen10102EfficiencyMB00.
10.
20.
30.
40.
50.
60.
70.
80.
91L2CalorimeterIsolationL3PixelIsolationL3TrackerIsolation|16GeV,|gen(TpLowLumi,EfficiencyW0.
750.
80.
850.
90.
951EfficiencyMB00.
10.
20.
30.
40.
5L2CalorimeterIsolationL3PixelIsolationL3TrackerIsolation(a)(b)|22GeV,|gen(TpHighLumi,Figure17.
Eciencyofthethreeisolationalgorithmsonthereferencebackgroundmuonsasafunctionofeciencyforthereferencesignalmuonsat(a)lowand(b)highluminosity.
tracksegmentreconstructedisrequired,andthesumofthenumberofDTsegmentsandRPChitsmustexceedthree.
AtLevel-3,amuonmusthavemorethan5siliconhitsintotalfromthepixelsandsiliconstrips.
TheoveralleciencyformuonstopasstheLevel-1throughLevel-3singlemuontriggercriteriacumulativelyasafunctionofthegeneratedηisshowningure18.
Muonsweregeneratedatintheintervals510GeV/c,andb)pT>20GeV/c.
reconstructedpTis97%,butislowerinsomeparticularregionsbecauseofgapsinthegeometricalcoverageofthechambers.
Theeciencyturn-oncurvesasafunctionofthegeneratedpTfortwodierentpTthresholdsareshowningure19.
TheeciencyshownisthecumulativeLevel-1throughLevel-3eciency.
Thethresholdateachtriggerlevelisdenedat90%eciency(relativetotheplateaueciency),anditcanbeseenthattheimprovedpTresolutionateachsuccessivelevelsharpenstheturn-oncurve.
TheeciencyatLevel-3forhighpTmuonsisaround95%forthepTvaluesshown.
Additionally,fortheHLTtrigger,Level-2muoncandidatesmustsatisfythecalorimeterisolationcriteriaatthe97%eciencypointforthereferencesignal.
AtLevel-3,candidatesmustsatisfythetrackerandpixelisolationcriteria(hereaftercollectivelyreferredtoas"trackerisolation"intheguresthatfollow)bothatthe97%eciencypointforthereferencesignal.
ThesinglemuontriggerratesasafunctionofthepTthresholdareshowningure20forbothlowluminosity(L=2*1033cm2s1)andhighluminosity(L=1034cm2s1).
CMSHighLevelTrigger39Figure20.
TheHLTsingle-muontriggerratesasafunctionofthepTthresholdfor(a)lowluminosityand(b)highluminosity.
TheratesareshownseparatelyforLevel-1,Level-2,andLevel-3,withandwithoutisolationappliedatLevels2and3.
Therategeneratedinthesimulationisalsoshown.
TheratesareshownseparatelyforLevel-1,Level-2,andLevel-3,withandwithoutisolationappliedatLevels2and3.
Alsoshownisthesinglemuonratethatwasgeneratedinthesimulation.
TheinclusivemuonsampleconsistsofQCDbackgroundevents(e.
g.
pionandkaonsdecayingintomuons),andgenuinepromptmuonproductionprocessessuchasW,Zandheavyavorproduction.
Thedetailsaregivenin[9].
DuetothepTresolutionofthetriggerthetriggerratescanbehigherthanthegeneratedrates.
Atlowluminosity,theLevel-3inclusivesingle-muontriggerratecanbereducedto30HzwithapTthresholdof18GeV/cwhentheisolationcriteriaareapplied.
Therateisabout100HzwithoutisolationatLevel-3forthesamethreshold.
Athighluminosity,athresholdof38GeV/creducesthesingle-muonLevel-3rateto30Hzwithisolation(50Hzwithoutisolation),andathresholdof31GeV/cyieldsarateof50Hz(100Hzwithoutisolation).
Thereasonwhyisolationachieveslessrejectionathigherthresholdscanbeunderstoodfromgure21,whichshowsthecontributionstotheLevel-3triggerrateathighluminosityfromallsourcesofmuonsbeforeandafterallisolationcriteriahavebeenapplied.
Theisolationcriteriastronglysuppressthecontributionsfromb,c,K,andπdecays.
ThisreducestheHLTratelessathighthresholds,however,wherethesingle-muonrateisdominatedbyW→νdecays.
Aftertheisolationcriteria,Wdecaysaccountfor50%(80%)oftheinclusivesingle-muonrateforathresholdof18GeV/c(31GeV/c)forlow(high)luminosity.
TheeciencyoftheHLTsingle-muontriggertoselectW→νandtt→+Xevents,whereoneofthetopquarksisrequiredtodecayinW→ν,isshowningure22asafunctionofthepTthresholdatlowluminosity.
ThresholdsaredenedasthepTvalueforwhichtheeciencyformuonsis90%ofthemaximumattainableeciency.
Approximately70%ofboththeWandtopquarkdecaysthathaveamuonintheducialregion|η|10GeV/c(pT>18GeV/c)atlow(high)luminosity.
Thisvalue,whichislowerthanthatproposedintheprevioussection,leadstoaconservativeCPUestimatebecauselowerpTmuonstakemoretimetoreconstruct.
ThesamepTthresholdsareappliedatLevel-2andLevel-3.
Alsoshowninthetable,isthetimetocompletetheHLTalgorithmexcludingtheGEANEroutineforpropagationthroughiron,whichissignicantlylessthatthetotaltime.
ClearlytherearesubstantialgainstobemadebyreplacingGEANEwithafastermethod.
ForcalorimeterisolationGEANEisusedforpropagationtotheECAL/HCALboundary.
ThetotaltimelistedinthelastrowrepresentstheaveragetimespentperLevel-1eventbythemuonHLTalgorithms,factoringintherejectionpowerateachlevelthatreducestheratetothenextlevel.
Thistimeamountstoapproximately700msperLevel-1accept,includingthetimespentinGEANE.
5.
JetIdentication5.
1.
HighLevelTriggerJetSelectionToidentifyandselectajetobjectatHLT,asimpleandfastiterativeseedconealgorithmisused.
Thealgorithmusesallthecalorimetertowersandhastwoparameters:(i)theCMSHighLevelTrigger44Table12.
CPUusageofthemuonHLTalgorithmsatlowandhighluminosityon1GHzprocessors.
Thevaluesgivenrepresenttheaveragetimetoprocessaneventpassingtheprevioustriggerlevel.
AlsolistedisthetimewithoutthecontributionoftheGEANEpropagationroutineMeanCPUTime(ms/event)MeanCPUTime(ms/event)L=2*1033cm2s1L=1034cm2s1pT>10GeV/cpT>18GeV/cHLTAlgorithmTotalExcludingGEANETotalExcludingGEANELevel-2640100580100Calorimeterisolation100259040Level-3420200590420Pixelisolation6565320320Trackerisolation190190370370Total/L1event710125660150sizeoftheconeR=√η2+φ2inη-φspaceand(ii)theseedthreshold.
Partonsafterhadronizationare"clustered"atparticlelevelintogenerator-jetsandmatchedinηφwiththereconstructedjets.
Atthepartonlevel,thejetenergyiscontainedinareasonablynarrowconeinηφspace.
Takingintoaccountsoftgluonemissionthejetenergyresolutionisoptimizedforalargerconesize.
Howeverwhenthejetsarereconstructedfromcalorimetertowers,thelargertheconeused,thegreaterthenoisecontribution,bothduetotheelectronicsandduetothepileupplusunderlyingeventenergydepositions.
ThejetenergyresolutionisdenedastheR.
M.
S.
ofthedierencebetweenthegenerator-leveljetETandthereconstructedjetETdividedbythegenerator-leveljetET(s/ET).
Acomparisonathighluminosityconditionsofthejetenergyresolutionisshowningure25for0.
5and0.
7conejetsandfortworapidityregions,|η|20GeVwithareasonableeciencywhilesuppressingfakejets.
ForthisstudythediscriminatingvariableusedisthefractionofthejetETcontainedina0.
25cone.
Foran80%eciencyofselectingrealjets(matchedinη-φwiththegeneratorleveljet),abouthalfofthefakejetsarerejected.
5.
2.
JetEnergyScaleCorrectionsTheCMScalorimetersystemisoptimizedfortheprecisionmeasurementofelectronsandphotons.
Ithasanon-linearresponsetopions.
Sincetheenergyofatypicalpioninajetisroughlyproportionalto1/sinθ,theresponseofthecalorimetertojetsofagiventransverseenergyvarieswithηrequiringjetenergy-scalecorrections.
Thejetenergyhastoalsobecorrectedfornoiseintheelectronicsandforpileupenergy.
CMSHighLevelTrigger47Figure28.
Signaleciencyversusbackgroundeciencyforremovingfakejets.
ThefractionofthejetETina0.
25coneisusedasadiscriminatingvariable.
TheMonteCarlojetsarecalibratedonaveragetothegeneratorjetenergy.
Thistechniqueisexpectedtoyieldresultsthatarevirtuallyidenticaltothosethatwouldbeobtainedfromafullcalibrationusingphoton-jetbalancinginphotonplusjetdata.
Figure29showsthesizeofthetypicalcorrectionforHLTjetsobtainedfromsimulation,forlowandhighluminosityrunningconditions.
Thecorrectioncanbeaslargeas20%forlow-ET(40GeV)jets.
Themaineectofthecorrectionsistheremovaloftheηdependencefromthetriggereciency,whilethejetenergyresolutionisimprovedonlyslightly.
TheresolutionoftheETmeasurementforjetsbeforeandaftercorrections,atbothlowandhighluminosity,isshowningure30forcone0.
5jets.
TheresolutionforhighETjets(ET>300GeV)issimilaratlowandhighluminosity,whiletheresolutionatlowerETvaluesissignicantlyworseathighluminosity.
5.
3.
JetRatesThejetratesshouldbeinsensitivetothedetailsofthesimulationandrobustagainstplausiblechangesinjetalgorithms.
Figure31showsthesinglejettriggerrates(atlowandhighluminosity)forjetsreconstructedatthegeneratorlevelusingparticlesfromonlythehardscattering(labeled"SignalGenJet")andusinggenerator-levelparticlesfromallinteractions(labeled"in-timeGenJet").
ThegurealsoshowstheHLTjetratesbothbeforeandafterjetenergyscalecorrections.
AtxedET,thehighluminosityratesareaboutvetimeslargerthantheratesatlowluminosity,asexpected.
Figure32showstheHLTratesofsingle,3-and4-jettriggersatlowandhighluminosityasafunctionofthecalibratedjetETthreshold.
CMSHighLevelTrigger4800.
20.
40.
60.
811.
21.
450100150200250300350400ParticleJetEt(GeV)EtCALOJET/EtPARTJETcalibratedjetsrawjetsL=2x1033cm-2s-1Jets(R=0.
5)ηEtCALOJET/EtPARTJETcalibratedjetsrawjetsL=2x1033cm-2s-1Jets(R=0.
5)00.
20.
40.
60.
811.
21.
400.
511.
522.
533.
544.
5500.
20.
40.
60.
811.
21.
450100150200250300350400ParticleJetEt(GeV)EtCALOJET/EtPARTJETcalibratedjetsrawjetsL=1034cm-2s-1Jets(R=0.
5)ηEtCALOJET/EtPARTJETcalibratedjetsrawjetsL=1034cm-2s-1Jets(R=0.
5)00.
20.
40.
60.
811.
21.
400.
511.
522.
533.
544.
55Figure29.
RatioofreconstructedovergeneratedjetETforHLTjetsversusgeneratedETandη,beforeandafterjetenergyscalecorrectionsfor(left)lowand(right)highluminosity.
Figure30.
ResolutionforHLTjetsbefore(triangles)andafter(circles)jetenergyscalecalibration.
Low(left)andhigh(right)luminosity.
CMSHighLevelTrigger4910-210-111010210310410510610702004006008001000qIn-timeGenJetsHLTcorrected5HLTuncorrectedvSignalGenjetSingleJetETCutoff(GeV)Rate(Hz)Figure31.
Generatedsingle-jetratesasafunctionofthejetETthresholdclusteringonlyparticlesfromthehardscattering(GenJet)andallparticles–includingthosefromthepileupinteractions(in-timeGenJet).
AlsoshowntheHLTsingle-jettriggerratesbeforeandafterjetenergyscalecorrections.
Theopen(lled)symbolscorrespondtothelow(high)luminosity.
Figure32.
HLTratesforsingle,3,and4-jettriggersasafunctionofthecalibratedjetETonthexaxis(blue/darkercurves).
Thesameplotshowsalsotherateforthethresholdthatgives95%eciencyforthegenerator-ETonthexaxis(red/lightercurves).
Resultsareforlow(left)andhigh(right)luminosity.
CMSHighLevelTrigger50Table13.
Jetratesummarytable.
Thetablegivesthegenerator-leveljetETwherethethreshold(inGeV)onthereconstructedjetETgives95%eciency.
TheactualvalueofthethresholdonETthatcorrespondstothe95%eciencypointsisgiveninparenthesis.
Thethresholdischosentogivearateof1kHz(Level-1)and1Hz(HLT).
1-jettrigger2-jettrigger3-jettrigger4-jettriggerGeVGeVGeVGeVlowluminosityLevel-1177(135)140(104)85(57)70(45)highluminosityLevel-1248(195)199(153)112(79)95(64)lowluminosityHLT657(571)564(489)247(209)149(122)highluminosityHLT860(752)748(652)326(275)199(162)Thegenerator-levelETofjetswith95%triggereciency(HLTorL1)thatcorrespondstoagiventhresholdoncalibratedandreconstructedjetsisshowningure32andtable13.
Therelationshipbetweenthevalueofthethresholdandthegenerator-leveljetETislinear.
Notethatthedemocratic1kHzatL1and1HzatHLTperjettriggerrateisaworkingexample.
TheETthresholdsforexclusivejettriggersareveryhigh.
MostHLTphysicstriggersrequirereasonablylowjetETthresholdsandadditionalphysicsobjects(e.
g.
leptons,photons)resultinginacceptablerates.
6.
MissingEnergyIdenticationThecalorimeterinformationisusedtomeasurethemissingtransverseenergy(E/T,METorEmissT)andidentifyneutrinosorotherweaklyinteractingparticlesthatescapedetection.
AsimplealgorithmcalculatestheE/TasthenegativevectorsumoftheETofalltowers(aboveathresholdofET(tower)>500MeV).
Thepolarangleofeachtowercenteriscalculatedwithrespecttoz=0.
AlgorithmsthatincorporatejetenergyscalecorrectionsintheE/Treconstructionhavebeenstudied.
Inthereferedtoas"Type-I"E/TcorrectionsuncorrectedjetswithET>30arevectoriallysubtractedfromtheE/Tandcorrectedjetsarevectoriallyadded,whilenocorrectionisappliedfortheunclusteredenergy.
In"Type-II"E/TcorrectionsthejetenergyscalecorrectionsforjetswithET>30GeVareusedandinadditiontheunclusteredtowersarecorrected.
Figure33showsthemeandierencebetweenthegenerator-levelE/TandthereconstructedE/TforthreedierentE/Talgorithmsasafunctionofthegenerator-levelE/T.
ThestudyusesaSUSYsamplegeneratedwithsquarkandgluinomassesof500GeV/c2wherethenalstateismultijetsandlargemissingenergyfromtheneutralinos.
ThesamegurealsoshowstheRMSofthisdierence.
ThejetenergyscalecorrectionsresettheE/Tenergyscale,butdonotimprovetheE/Tresolution.
CMSHighLevelTrigger51-100-80-60-40-2002040050100150200250300350400450MCMET,GeV020406080100050100150200250300350400450MCMET,GeVFigure33.
(Left)Meandierencebetweenthegenerator-levelE/TandthereconstructedE/TforthreedierentE/Talgorithmsasafunctionofgenerator-levelE/T.
(Right)R.
M.
Softhedierenceasafunctionofthegenerator-levelE/T.
TheanalysisisdoneforL=2*1033cm2s1.
6.
1.
E/TRatesAlargesourceofbackgroundforE/Ttriggersisinclusivedi-jetproduction.
LargemismeasurementsareexpectedwhenonejetimpactsinalowresponsepartofthecalorimeterinwhichcasetheE/Twilltendtobealongthedirectionoftheunder-measuredjet.
AtlargeE/TecientrejectionofmismeasuredQCDeventscanbeachievedusingtheφcorrelationbetweentheleadingandsecondleadingjet.
Figure34showstherateswhenajetwithETaboveagiventhresholdisalsorequiredaspartofthetrigger.
Tofacilitatecomparisonsbetweendierentalgorithmsandexperimentsweplottheratesasafunctionoftherequirementthatcorrespondsto95%eciencyforagivengenerator-levelE/T.
Thereferenceprocessusedtodenethemappingbetweengenerator-levelE/TandreconstructedE/TisHiggsproductionviavector-bosonfusionanddecayinWWwithanalstateoftwoleptonsandmissingenergy.
Therateplotsdependonthesignalsamplethatwasusedtoperformthismapping.
Abovegenerator-levelE/Tofabout50GeV,therelationshipbetweenthecutvalueandthegenerator-levelE/Tisapproximatelylinear.
Figure35showstheseratesatbothlowandhighluminosityforLevel-1andHLTE/T.
StudiesofexplicitphysicsHLTselectionwithE/Taregiveninsection9.
CMSHighLevelTrigger52Figure34.
EventratesasfunctionofE/Twhenrequiringajetaboveathresholdasmarkedfor(left)lowluminosityand(right)highluminosity.
Figure35.
RateversustheE/Trequirementthatgives95%eciencyforagivengeneratedE/Tatlow(left)andhigh(right)luminosity.
ThereferencesampleusedforthemappingofthegeneratedandtheoineE/TisaHiggssamplewithdi-leptonsplusmissingenergyinthenalstate.
ThecrossescorrespondtotheLevel-1rate,thecirclestotheHLTrate,andthetrianglestotherateforacorrectedE/TalgorithmappliedattheHLT.
CMSHighLevelTrigger53Table14.
CPUrequirementsforjetandE/TreconstructionintheHLT.
Timesarein1GHzCPUms.
DataSampleA/H→ττinclusivedi-jetsMH=500GeV/c25014GeV/c,–pTτjet>30GeV/c,–|η|45GeV/c,–|ητjet|80GeV/c,–|ητjet|50GeV98%ofthetransverseenergyiscontainedinaconeof0.
4.
Thereforeweuseasaselectioncriterionthelevelofisolationoftheτ-candidatejetintheelectromagneticcalorimeter.
WedenePisolas:Pisol=R200GeV.
Theentireselectionprocedureisveryfast,asisshownintable15wherethetimesrequiredtobuildcalorimetertowers,forregionaljet-ndingandforthecalculationoftheisolationparameterPisolarelisted.
CMSHighLevelTrigger567.
2.
Pixel-basedτselectionTheidenticationofaτ-jetusingchargedparticletracksisalsobasedonisolationcriteria.
Calorimetertriggersprovidearegioninwhichisolatedgroupsoftracksthatarewellmatchedtothejetaxisgivenbythecalorimetercanbesearchedfor.
Thecorrespondingisolationcriteriarequirethereconstructionoflow-pTtrackswithgoodeciencyandanacceptablylowfakerate.
AprecisemeasurementofthetrackpTisnotnecessary.
Afasttrack-ndingalgorithmusingonlypixeldatameetstheserequirements.
Identicationofτ-jetswiththepixeldetectorwillbereferredtoasthe"PixeltrackTau"trigger.
Theprincipleofτ-jetidenticationusingthepixeldetectorisshowningure37.
Thedirectionoftheτ-jetisdenedbytheaxisofthecalorimeterjet(denoted"Lvl-2τ-jetaxis").
Thetrack-ndingalgorithmrstreconstructsalltrackcandidates("pixellines")andthentheinteractionverticesfromthetracksusingahistogrammingmethod.
TrackcandidatesinamatchingconeRmaroundthejetdirectionandaboveathresholdpTmareconsideredinthesearchforthesignaltracks.
Theleadingsignaltrack(tr1ingure37)isdenedasthetrackwiththehighestpT.
Similarly,thevertexfromwhichtheleadingsignaltrackoriginatesisconsideredtobethesignalvertex(SV).
AnyothertrackfromtheSVwhichiswithinthenarrowsignalconeRsaroundtr1isassumedtooriginatefromtheτdecay.
TracksconsistentwiththeSV(within2mmoftheSV)andwithtransversemomentumaboveathresholdpTiarethensearchedforinsidealargerconeofopeningangleRi.
IfnotracksarefoundintheRiconeexceptfortheoneswhicharealreadyintheRscone,theisolationcriteriaarefullled.
TheoptimalvaluesoftheconesizeRm,signalconesizeRs,andthethresholdspTmandpTifor1-and3-prongτ-jetsfromA0/H0→ττdecaysandforHiggsmassMH≥200GeV/c2are:Rs=0.
07,Rm=0.
10,pTm=3GeV/candpTi=1GeV/c[28].
TheonlyremainingfreeparameteristhesizeoftheisolationconeRi.
TheeciencyofthePixeltrackTautrigger,atbothlowandhighluminosityisshowningure38whenthesizeoftheisolationconeisvariedintherangeof0.
20-0.
50.
PixelτidenticationhasbeenappliedtotherstcalorimeterjetinA0/H0→ττ→2τ-jetandQCDdi-jetevents.
Thedegradationoftheperformanceathighcomparedtolowluminosityisduetohighpixeldetectoroccupancythatresultsinreadoutineciencyaswellasthecontaminationofcharged-particletracksfrompileupintheisolationconecomingfromavertexotherthanthehardcollisionvertex.
TheselectionisindependentoftheHiggsmass.
ComparisonbetweenthefullandstagedpixelsystemsshowsthatatconstantQCDbackgroundrate,thesignaleciencyisdegradedbyapproximately10%inthestagedconguration.
ThetimingperformanceofthePixeltrackTautriggeralgorithmisshownintable16.
Itincludesthetimetoreconstructclustersfromthedigitizedpixeldataandthereconstructiontimeofthepixellinesandvertices.
Thetimeusedbytheisolationalgorithmitselfisnegligible.
CMSHighLevelTrigger57isolationconeRijet-trackmatchingconeRmsignalconeRsLvl-2τ-jetaxistr1ppFigure37.
Sketchofthebasicprincipleofτ-jetidenticationusingchargedparticletracks.
0.
40.
50.
60.
70.
80.
9100.
020.
040.
060.
080.
10.
120.
140.
160.
18ε(QCD50-170GeV)ε(H(200,500GeV)→ττ,τ→1,3h+X)RS=0.
07,RIisvaried0.
2-0.
5RM=0.
10L=2*1033cm-2s-1PxlTauTriggeronfirstCalojetMH=200GeV,notstagedPxlMH=500GeV,notstagedPxlMH=200GeV,stagedPxlMH=500GeV,stagedPxl0.
40.
50.
60.
70.
80.
9100.
020.
040.
060.
080.
10.
120.
140.
160.
18ε(QCD50-170GeV)ε(H(200,500GeV)→ττ,τ→1,3h+X)RS=0.
07,RIisvaried0.
2-0.
5RM=0.
10L=1034cm-2s-1PxlTauTriggeronfirstCalojetMH=200GeVMH=500GeVFigure38.
EciencyofPixeltrackTauTriggerfortherstcalorimeterjetinA0/H0→ττ→2τ-jet,fortwoHiggsmasses(MH=200and500GeV/c2)versustheeciencyforQCDdi-jetbackgroundeventsat(left)L=2*1033cm2s1(resultsforboththefullandthestagedpixelsystemcongurationsareshown)and(right)L=1034cm2s1.
CMSHighLevelTrigger58Table16.
CPUtime,inmsofa1GHzCPU,forτ-jetidenticationwiththepixeldetectorforQCDdi-jetevents.
Time(ms)Reconstructionstep2*1033cm2s11034cm2s1Buildclustersfrompixeldigitizeddata44100Reconstructpixellinesandvertices34262Totaltime783627.
3.
RegionaltrackndingτselectionIdenticationandselectionofτ-jetsisalsoperformedusinginformationfromtracksreconstructedwiththefullSiliconStripTracker.
Thisselectionwillbereferredtoasthe"TrackTau"trigger[29].
TheTrackTautriggerperformsthereconstructionofonlythosetracksinrestrictedregionsofinterest(regionaltracking),denedbytheconesaroundeachjetdirectiongivenbythecalorimeterjetreconstruction.
Thesignalvertexisrstselectedusingthepixeldetector,asthevertexwiththemaximum|PT|oftheassociatedpixellines.
Theregionaltrackingtechniqueisappliedattheseedinglevel(regionalseeding)inordertominimizetheseedmultiplicity,signicantlyreducingtheCPUtimeofthealgorithm.
AspecialtracknderusespixellinesinaconeofR=0.
5aroundthecalorimeterjetdirectionastrackseeds.
Aftertrackreconstruction,onlytrackscompatiblewiththesignalvertexaretakenintoaccount.
Afurtherimprovementofthetimingperformanceisobtainedbystoppingthetrackreconstructionwhensixhitshavebeenassociatedwiththetrackhelix.
Thisgivesanacceptableresolutiononthetrackparametersandalowfakerate.
Attheseedinglevelanoptionisadoptedwhichusestwopixelhitsoutofthreepixellayers("2-hitrecovery")sinceitincreasestheseedingeciency.
TheTrackTautriggerreliesonanisolationrequirementsimilartotheoneusedinthePixelTautrigger.
Toreducethecontaminationfromsofttracks,onlytrackswithpT>1GeV/candz0compatiblewiththezpositionofthesignalvertex(within2mm)areconsidered.
Thenumberoftrackswithinasignalconeandwithinanisolationconearecounted.
Theconesaredenedaroundthedirectionoftheleadingtrackwhichisthehighest-pTtrackfoundinthematchingcone(Rm=0.
1)aroundthecalorimeterjetdirection.
Theisolationrequirementisthattherebenotracksintheisolationconeexceptthosecontainedwithintheinner,signal,cone.
Theconesizesarechosentooptimizethesignaleciencyandbackgroundrejectionandalsotominimizethedependenceoftheeciencyonthejetenergy.
Higherbackgroundreductioncanbeobtainedbyrequiringthetransversemomentumoftheleadingtrack,pTLT,toexceedafewGeV/c.
DuetothestrongdependenceofthetrackpTspectrumontheHiggsmassandontheτhadronicdecaymode,theleadingtracktransversemomentumrequirementiscarefullyoptimized.
Figure39showstheTrackTautriggerperformancewhenappliedtotherstcalorimeterCMSHighLevelTrigger590.
40.
50.
60.
70.
80.
9100.
020.
040.
060.
080.
10.
120.
140.
160.
18ε(QCD50-170GeV)ε(H(200,500GeV)→ττ,τ→1,3h+X)MH=200GeV,stagedPxlMH=500GeV,stagedPxlMH=200GeV,notstagedPxlMH=500GeV,notstagedPxlMH=200GeVMH=500GeVRM=0.
1L=2x1033cm-2s-1PTLT>6GeVRS=0.
07,RIisvaried0.
2-0.
45TrkTauTriggeronfirstCalojet0.
40.
50.
60.
70.
80.
9100.
020.
040.
060.
080.
10.
120.
140.
160.
18ε(QCD50-170GeV)ε(H(200,500GeV)→ττ,τ→1,3h+X)MH=200GeVMH=500GeVRM=0.
1L=1034cm-2s-1,notstagedPxlPTLT>7GeVRS=0.
065,RIisvaried0.
2-0.
45TrkTauTriggeronfirstCalojetFigure39.
TrackTautriggereciencyfortherstcalorimeterjetinA0/H0→ττ→2τ-jetversustheeciencyforQCDdi-jetbackgroundeventsforMH=200and500GeV/c2.
Theresultsareshownbothwiththefullandthestagedpixelsystemsfor(left)L=2*1033cm2s1,andwiththefullpixelsystemfor(right)L=1034cm2s1.
jetinA0/H0→ττ→2τ-jetsignalevents,andtoQCDdi-jetbackgroundevents.
ThedierentpointscorrespondtodierentsizesoftheisolationconeRiwhichwasvariedbetween0.
2and0.
45.
TheperformanceatL=2*1033cm2s1isstudiedforboththefullandstagedpixeldetectorcongurations.
ForthesameQCDdi-jetbackgroundeciency,thesignaleciencyisreducedbyabout15%inthestagedpixelscenario.
SincethealgorithmhastofulllstringentCPUtimelimitationsparticularattentionhasbeenpaidtoitsoptimization.
7.
4.
MSSMneutralHiggs2τ-jetselectionwithCalorimeterandPixelTauTriggersAcompleteHLTselectionforA0/H0→ττ→2τ-jeteventscanbedenedusingtheCalorimeterTautriggerselectionappliedtotherstcalorimeterjet,andthePixeltrackTautriggerselectionappliedtobothcalorimeterjets.
Table17givesthepurityoftheselectedjetsingg→bbA0/H0,A0/H0→ττ→2τ-jeteventswithMH=500GeV/c2,denedasthefractionofcalorimeterjetswhichcorrespondtoatrueτ-jet.
Toincreasethepurityofthesecondjetthefollowingsearchalgorithmisapplied:ifasecondLevel-1τ-jetdoesnotexistinthelistorifitexistsbuttheETofthesecondcalorimeterjetislessthan50(70)GeVatlow(high)luminosity,anewcalorimeterjetintheregioncenteredontherstLevel-1centraljetisreconstructed.
Thepurityofthesecondjetwhenchoseninsuchawayisincreasedtoabout90%(thenumbersinparenthesesintable17correspondtothepurityoftheselectionwhenthisre-denitionalgorithmisnotapplied).
UsageoftheCalorimeterTautriggerasapre-selectorbeforeapplyingthePixeltrackTautriggerallowsconsiderablereductionofthetotalCPUtimeperCMSHighLevelTrigger60Table17.
PurityofcalorimeterjetsinA0/H0→ττ→2τ-jeteventsatlowandhighluminosity.
Numbersforthesecondjetwithout(with)parenthesesarethepurityafter(before)re-denitionofthesecondjet(seetext).
L=2*1033cm2s1L=1034cm2s11stjet2ndjet1stjet2ndjet0.
980.
90(0.
63)0.
980.
88(0.
65)Table18.
EciencyforA0/H0→ττ→2τ-jetevents,andtotalCPUtime(Ttot),asafunctionofthecalorimeterisolationrequirement(Pisol)anditsbackgroundrejectionfactor(Scalo)atL=2*1033cm2s1.
Anoverallsuppressionfactor103forbackgroundeventsismaintained.
Theboldedcolumncorrespondstotheoperatingpoint.
PisolGeV-10.
47.
65.
64.
64.
03.
43.
22.
6Scalo1.
01.
52.
03.
04.
05.
06.
27.
510.
0Ttot(ms)1108572595250454341calo+pixel%353740414039373635event.
TherequirementsareoptimizedbyexaminingthebackgroundrejectionoftheCalorimeterTautriggerstep(Scalo),theeciencyforthesignal,andtheCPUtimeusage,whilekeepingasuppressionfactorofthefullHLTselectionof103.
ResultsofsuchastudyforMH=200GeV/c2arepresentedintable18forlowluminosityrunningconditionswiththefullpixelsystem.
Ithasbeenfoundthatforatotalsuppressionfactorof103,atbothlowandhighluminosity,acalorimetersuppressionfactorofthreeyieldsthehighestsignaleciency.
Atthisoperatingpoint(Pisol=5.
6GeV)thetotaltimeTtotofthefullpathis59msforlowluminosityand174msforhighluminosity.
Figure40showstheeciencyoftheCalorimeter+PixeltrackTautriggerselectionforthesignalandforQCDdi-jetbackgroundeventsatlowandhighluminosity.
ThesizeoftheisolationconeRiisvariedintherangebetween0.
20and0.
50,andtheoptimalsuppressionfactorof3fortheCalorimeterTautriggerisused.
Foratotalsuppressionfactorofabout103,thereislittledierenceintheeciencybetweenthestagedandfullpixelcongurationsatlowluminosity.
7.
5.
MSSMneutralHiggs2τjetselectionwiththeTrackTautrigger.
ThissectionpresentstheperformanceofacompleteHLTselectionforA0/H0→ττ→2τ-jet,whentheCalorimeterTautriggerselection,appliedontherstcalorimeterjet,isfollowedbytheTrackTautriggeronbothcalorimeterjets(Calo+TrackTautriggerpath).
Figure41showsthesignalversusbackgroundeciencywhentheTrackTautriggerselectionisappliedtobothcalorimeterjets,atlowluminosity(left),forboththecompleteandstagedpixeldetector,andathighluminosity(right).
ThedierentpointsCMSHighLevelTrigger610.
20.
250.
30.
350.
40.
450.
50.
550.
60.
650.
710-310-2ε(QCDbkg50-170GeV)ε(H(200,500GeV)→ττ,τ→1,3h+X)Calo+PxlTauTriggerL=2*1033cm-2s-1RS=0.
07,RIisvaried0.
2-0.
5RM=0.
10Pem=5.
6GeVMH=200GeV,notstagedPxlMH=500GeV,notstagedPxlMH=200GeV,stagedPxlMH=500GeV,stagedPxl0.
20.
250.
30.
350.
40.
450.
50.
550.
60.
650.
710-310-2ε(QCDbkg50-170GeV)ε(H(200,500GeV)→ττ,τ→1,3h+X)L=1034cm-2s-1Calo+PxlTauTriggerRS=0.
07,RIisvaried0.
2-0.
5RM=0.
10Pem=9.
8GeVMH=200GeVMH=500GeVFigure40.
EciencyoftheCalo+PixelTautriggerpathforA0/H0→ττ→2τ-jetandQCD2-jetbackgroundeventswhenthesizeoftheisolationconeRiisvariedintherange0.
20-0.
50.
Theoptimalsuppressionfactorof3fortheCaloTautriggeristaken.
ResultsareshownfortwoHiggsmasses,MH=200and500GeV/c2,andfor(left)L=2*1033cm2s1withthefullandstagedpixelsystems,and(right)L=1034cm2s1.
correspondtodierentsizesoftheisolationcone,Ri,whichisvariedbetween0.
2and0.
45.
A6(7)GeV/crequirementonthepToftheleadingtrackisappliedatlow(high)luminositytoreachabackgroundrejectionfactorof103.
AtaQCDdi-jetbackgroundeciencyof103thesignaleciencywiththestagedpixeldetectorisreducedby20%.
Figure42showsthesignalversusbackgroundeciencywhentheCalorimeterTautriggerselectionappliedontherstcalorimeterjet,isfollowedbytheTrackTautriggeronbothcalorimeterjets(Calo+TrackTautriggerpath).
Table19summarizestheeciencyoftheTrackTautriggerattheoperatingpointswherethebackgroundrejectionfactoris103.
Thesepointshavebeenchosentakingintoaccounttheoverallperformanceandminimizingtheτ-jetenergydependencyofthesignaleciency.
Thethirdandfthrowsoftable19listtheeciencyatlowandhighluminosityforthefullCalo+TrackTautriggerselection.
TheTrackTautriggerCPUtimedistributionisshowningure43forHiggsandQCDdi-jetbackgroundeventsatlowluminosity.
Thetimeneededforadoubletagisonlyslightlylargerthanthetimeneededforasingletag,sincethesecondcalorimeterjetisanalyzedonlyinthe6%ofbackgroundeventswhichpassthesingletagontherstcalorimeterjet.
Only10%oftheQCDeventsrequiremorethan400mstobeanalyzed.
AnimportantadvantageoftheCalo+TrackTautriggerselectionoverthesimpleTrackTautriggerisitsbettertimeperformance,whichisduetothefactthatonlythoseeventswhichpassthecalorimeterτselectionontherstjetneedtobeanalyzedbytheTrackTautrigger.
Followingthesamemethoddescribedinsection7.
4andusingthenumbersfromtable18(Scalo=3,Tcalo33ms)anaveragetimeofabout130ms/eventisexpectedatlowluminosity.
CMSHighLevelTrigger620.
20.
250.
30.
350.
40.
450.
50.
550.
60.
650.
710-310-2ε(QCD50-170GeV)ε(H(200,500GeV)→ττ,τ→1,3h+X)MH=200GeV,stagedPxlMH=500GeV,stagedPxlMH=200GeV,notstagedPxlMH=500GeV,notstagedPxlMH=200GeVMH=500GeVPTLT>6GeVRS=0.
07,RIisvaried0.
2-0.
45RM=0.
1L=2x1033cm-2s-1TrkTauTrigger0.
20.
250.
30.
350.
40.
450.
50.
550.
60.
650.
710-310-2ε(QCD50-170GeV)ε(H(200,500GeV)→ττ,τ→1,3h+X)MH=200GeVMH=500GeVPTLT>7GeVRS=0.
065,RIisvaried0.
2-0.
45RM=0.
1L=1034cm-2s-1,notstagedPxlTrkTauTriggerFigure41.
EciencyoftheTrackTautriggerappliedtobothCalojetsinA0/H0→ττ→2τ-jetversusthatinQCDdi-jetevents.
ResultsareshownfortwoHiggsmasses,MH=200and500GeV/c2,andfor(left)L=2*1033cm2s1withthefullandstagedpixelsystems,and(right)L=1034cm2s1.
Table19.
SummaryofTrackTautriggereciencywhentwoCalojetsaretaggedinA0/H0→ττ→2τ-jetevents.
ThethirdandfthrowsshowtheresultswhentheCalorimeterTautriggerselectionappliedontherstCalojetisfollowedbytheTrackTautriggeronbothCalojets.
AQCDdi-jetbackgroundrejection(lastcolumn)of103isrequired.
DuetothelimitedMonteCarlostatisticssomestatisticalerrorsfortheQCDbackgroundarelarge.
LuminosityConguration/MHMHQCDcm2s1Trigger200GeV/c2500GeV/c22*1033StagedpixelsTrackTau0.
355±0.
0060.
375±0.
005(8.
6±1.
6)*1042*1033FullpixelsTrackTau0.
433±0.
0060.
489±0.
005(8.
3±1.
6)*1042*1033FullpixelsCalo+TrackTau0.
446±0.
0060.
486±0.
005(1.
0±0.
2)*1031034TrackTau0.
346±0.
0060.
420±0.
005(1.
1±0.
4)*1031034Calo+TrackTau0.
361±0.
0060.
427±0.
005(9.
4±3.
0)*104ThetimerequiredbytheTrackTautriggerathighluminosityismuchlargerandiscurrentlyestimatedat1s/event.
However,makinguseoftheCalo+TrackTauTriggerselection,thistimewillbereducedtolessthan400ms/event.
Afurtherimprovementisexpectedwiththeuseofaregionalpixelreconstruction.
Tosummarize,theCalo+PixeltrackTautriggerandtheCalo+TrackTautriggerarethetwooptimalHLTpathsfortheselectionofMSSMA0andH0bosonsproducedintheprocessgg→bbA0/H0,A0/H0→ττ→2τ-jetevents(MH=200and500GeV/c2).
CMSHighLevelTrigger630.
20.
250.
30.
350.
40.
450.
50.
550.
60.
650.
710-310-2ε(QCD50-170GeV)ε(H(200,500GeV)→ττ,τ→1,3h+X)MH=200GeVMH=500GeVPTLT>6GeVRS=0.
08,RIisvaried0.
2-0.
45RM=0.
1L=2x1033cm-2s-1,notstagedPxlCalo+TrkTauTriggerPem=5.
6GeV0.
20.
250.
30.
350.
40.
450.
50.
550.
60.
650.
710-310-2ε(QCD50-170GeV)ε(H(200,500GeV)→ττ,τ→1,3h+X)MH=200GeVMH=500GeVPTLT>7GeVRS=0.
08,RIisvaried0.
2-0.
45RM=0.
1L=1034cm-2s-1,notstagedPxlCalo+TrkTauTriggerPem=9.
8GeVFigure42.
Calo+TrackTautriggereciencyforA0/H0→ττ→2τ-jetversusthatinQCDdi-jetevents.
TheCaloTautriggerselectionappliedontherstCalojetisfollowedbytheTrackTautriggeronbothcalorimeterjets.
ResultsareshownfortwoHiggsmassesMH=200and500GeV/c2forlow(high)luminosityontheleft(right).
00.
0250.
050.
0750.
10.
1250.
150.
1750.
200.
20.
40.
60.
811.
21.
41.
61.
82Mean0.
290QCDLOWLUMINOSITY00.
050.
10.
150.
20.
2500.
20.
40.
60.
811.
21.
41.
61.
82Mean0.
250Time(seconds)MH500LOWLUMINOSITYFigure43.
TrackTautriggerreconstructiontime(inseconds)fordoubletaggingatlowluminosity.
(Upper)QCDdi-jetevents.
(Lower)A0/H0→ττ→2τ-jetevents.
CMSHighLevelTrigger640.
450.
50.
550.
60.
650.
70.
750.
010.
020.
030.
040.
050.
060.
07ε(QCD50-170GeV)ε(H(200,400GeV)→τν,τ→1,3h+X)L=2x1033cm-2s-1,notstagedPxlTrkTauTriggerPTLTisvaried1.
-30.
GeVRM=0.
1RS=0.
065,RI=0.
4MH=400GeVMH=200GeV0.
450.
50.
550.
60.
650.
70.
750.
010.
020.
030.
040.
050.
060.
07ε(QCD50-170GeV)ε(H(200,400GeV)→τν,τ→1,3h+X)L=1034cm-2s-1,notstagedPxlTrkTauTriggerPTLTisvaried1.
-30.
GeVRM=0.
1RS=0.
06,RI=0.
4MH=400GeVMH=200GeVFigure44.
TrackTautriggereciencyforH+→τν→τ-jeteventsversustheQCDdi-jetbackgroundeciency.
TheresultsaregivenforMH=200GeV/c2andMH=400GeV/c2.
andfor(left)L=2*1033cm2s1,withthefullpixelsystem,and(right)L=1034cm2s1.
TheCalo+PixeltrackTautriggerisapproximatelytwiceasfastastheCalo+TrackTautrigger(59versus130msatlowluminosityand170versus400msathighluminosity),butis15%lessecient.
ThelossofCalo+PixeltrackTautriggereciencycouldbecompensatedforbyanincreaseoftheLevel-1bandwidthallocatedtothesingleanddoubleτtrigger.
7.
6.
MSSMchargedHiggsτ-jetselectionwiththeTrackTautrigger.
TheTrackTautriggerwillworkasthenalpartoftheselectionMSSMchargedHiggsbosonsintheprocessgb(g)→H+t(b),H+→τν→τ-jet,t→bjj.
TheLevel-1single-τtriggerfollowedbyanHLTselectionofeventswithE/T>65(95)GeVatlow(high)luminositygivesanoutputrateofabout30(70)Hz.
Theselectionmustprovideasuppressionfactorof30tomatchtheoutputbandwidthrequirements.
TheTrackTauTriggerselectionisappliedtothecalorimeterjetreconstructedintheregionoftherstLevel-1τ-jet.
Thepurityofthecalorimeterjetinthesignaleventsis85%.
TheisolationcriteriausedinthePixelorTrackTautriggerscannotprovidetherequiredsuppressionfactor.
AdditionalbackgroundrejectionisobtainedbyapplyingacutonthepToftheleadingtrackintheTrackTautrigger.
Figure44showstheTrackTautriggerecienciesforthesignalandQCDbackgroundeventspassingtheLevel-1single-τtrigger.
SincethecutonE/TandtheTrackTauselectioneciencyareuncorrelated[29],acutonE/ThasnotbeenappliedduetolimitedMonteCarlostatistics.
Thedierentpointsingure44correspondtovaryingtheleadingtrack,pTrequirement,pTLT,from1to30GeV/c.
TheisolationparametersusedareRm=0.
1,Rs=0.
065(0.
060)forlow(high)luminosity,andRi=0.
4.
Arejectionfactorof30canbereachedwitha20(25)GeV/cCMSHighLevelTrigger65Table20.
TrackTauTriggereciencyfortheprocessgb(g)→H+t(b),H+→τν→τ-jet,t→bjjandfortheQCDbackground.
Theecienciesforthesignalarepresentedforabackgroundsuppressionfactorof30.
SignalandbackgroundsamplesEciencyofTrackTautriggerLowLuminosityHighLuminositypTLT>20GeV/cpTLT>25GeV/cRs=0.
065Rs=0.
06H+→τνMH=200GeV/c20.
580±0.
0040.
534±0.
005MH=400GeV/c20.
579±0.
0040.
553±0.
006QCD500.
3).
Thisconditionavoidsmisidenticationinsignalevents(theτpurityinsignaleventsincreasesfrom61%to99%)withnegligibleeectontheoveralleciency.
Figure45showstheLevel-1e+eTautriggerrateatL=1034cm2s1asafunctionoftheelectronandτ-jetthresholdsusedintheeTautrigger.
Thedotswithnumbersonthee+eTautriggeriso-ratecurvesindicatetheLevel-1selectioneciencyforthesignal.
ForagivenLevel-1triggerrate,theeciencyincreaseswhentheelectronthresholdisreducedandtheτ-jetthresholdisraised.
ThisresultsfromthesteeplyfallingpTspectrumoftheelectroninthesignalchannel.
Figure46showstheincreaseinLevel-1eciencyobtainedbyusingthee+eTautrigger,asopposedtojustthesingleelectrontrigger,asafunctionoftheextrabandwidthwhichoneallocatestotheeTautrigger.
ThecurvesareeachobtainedbyxingthethresholdfortheelectronineTautriggerandvaryingthethresholdonτ-jet.
TheHLTselectionisappliedindependentlyontheelectronstreamandtheeTaustreamatLevel-2.
0andLevel-2.
5.
AtLevel-2.
0,athresholdisappliedonlyontheelectroncandidate(section3.
4).
AtLevel-2.
5,pixel/super-clustermatchingisusedfortheelectroncandidate(section3.
5)andtheτ-jetidenticationisappliedasdescribedinsection7.
2.
Table21showsthedetailsofthefullselectionforfourscenarios.
Inallcases,theeTautriggerusesa20GeVelectronthreshold(correspondingto25.
5GeVonCMSHighLevelTrigger66L1electronEtCut(GeV)1820222426283032L1taujetEtCut(GeV)556065707580859063.
4%62.
7%61.
8%60.
3%66.
0%64.
4%62.
8%67.
5%65.
6%68.
5%7kHz6.
7kHz7.
5kHz8.
0kHzL1Rate=6535HzL2Rate=3364HzL25Rate=333HzL1Effi=58.
4%L2Effi=51.
6%L25Effi=44.
6%L1RateandefficiencyL=1034cm-2s-1Figure45.
Level-1e+eTautriggerrateatL=1034cm2s1asafunctionoftheeandτ-jetthresholds,foraxedsingle-etriggerthreshold.
Aconstant6.
54kHzbandwidthisallocatedtothesingle-etrigger.
Thefourcurvescorrespondtotheadditionalbandwidthsof0.
14kHz,0.
39kHz,0.
85kHzand1.
28kHzforthefourscenarios,allocatedtotheeTautrigger.
Theverticallineat28GeVcorrespondstothesingle-etrigger.
Thevalueslistedintheupperrightcorneraretheratesandecienciesforthesingle-etriggeratLevel-1,Level-2.
0andLevel-2.
5.
Level-1AdditionnalRate(Hz)0500100015002000250000.
050.
10.
150.
2L=1034cm-2s-1Et≥18GeVeEt≥19GeVeEt≥20GeVeEt≥21GeVeEt≥22GeVeEt≥23GeVe(ε[eoreTau]-ε[e])/ε[e]atLevel-1Et≥24GeVeEt≥25GeVeEt≥26GeVeEt≥27GeVeEt≥28GeVeFigure46.
TheincreaseinLevel-1eciency,atL=1034cm2s1,obtainedusingthee+eTautrigger,asopposedtojustthesingleelectrontrigger,asafunctionoftheextrabandwidthallocatedtotheeTautrigger.
Eachcurveisobtainedbyxingtheelectronthreshold(Eetintheplot)andvaryingthethresholdfortheτ-jet.
CMSHighLevelTrigger67ElectronPt(GeV/c)020406080100120140050100150200250SpectrumrecoveryatL25L=1034cm-2s-1Figure47.
ElectronpTinA0/H0→ττ→e+τ-jeteventsatL=1034cm2s1.
ThelledportionofthehistogramcorrespondstothegainobservedatLevel-2.
5byaddingtheLevel-1e+τtrigger,theremainingunlledpartcorrespondstoelectronspassingthesingleelectrontrigger.
theLevel-195%eciencyscale)whiletheτthresholdisvariedinsuchawaythattherateaddedbytheeTautriggertothesingle-electrontriggerrateis0.
14kHz,0.
39kHz,0.
85kHzand1.
28kHzrespectively.
Acceptinganadditionalrateof0.
85kHzatLevel-1leadstoarelativeimprovementineciencyatLevel-2.
5ofabout10%,atapriceofa7Hzrateincrease.
Thisisillustratedingure47whichshowsthepTspectrumoftheelectronthatisrecoveredatLevel-2.
5whentheeTautriggerisaddedtothesingleelectrontriggeratLevel-1.
Sincethesingleelectronthresholdsarelowerinthelowluminosityscenario,lessisgainedbyaddingthecombinedeTautrigger.
TheHLTselectionschemeisthesameasathighluminositybuttheLevel-1thresholdsaredierent.
Forascenariowhere0.
82kHzfortheeTautriggerisaddedatLevel-1,therelativegainineciencyatLevel-2.
5is4%.
7.
8.
MSSMneutralHiggs+τ-jetHLTselectionThereconstructionecienciesandonlinebackgroundrejectionperformanceforA0/H0→ττ→+τ-jethavebeenstudiedforthecasewhentheHiggsparticleisproducedinassociationwithb-quarksandthemassofHiggsparticleis200GeV/c2.
Thestudiesfocusonhigh-luminosityrunningconditionswheretheeventselectionandbackgroundreductionaremoredicult.
ThequotedecienciesaregivenwithrespecttothebaselineMonteCarlosamplegeneratedwithpT>14GeV/c,pTτjet>30GeV/c,|η|70%cuTL1muonp05101520cut[GeV]TL1tauE020406080100120140833Hz4.
5e+05HzrrrrrrrrrFigure49.
Level-1triggereciencyasafunctionofthemuonpTandτ-jetETrequirementsforhighluminosity.
τeventsacceptedbythesingle-orsingle-τtriggerareincluded.
Thedierencebetweencontourlinesrepresentsachangeineciencyof1%.
TheLevel-1thresholdcorrespondingtotheoinerequirementselects70%ofthebaselineevents.
er/DAQprojectDataAcquisitionandHigh-LevelTriggernReport,VolumeII15PhysicsObjectSelectionandHLTPerformance62,theefficiencyoftheLevel-1τtriggerisshownasafunctionofPTandτET.
Onlyboththeτjetandthearefoundbythetrigger(irrespectiveoftheirPTandET)contributehecombinedtriggerincreasestheefficiencybyuptoamaximumof73%fortheloosePTInordertopreserveeventspassingtheofflinecutsPT>15GeV/c,ET≥40GeV,onecanorrespondingLevel-1workingpointwithLevel-1PT≥14GeV/candLevel-1ET>45GeVllefficiencyof70%.
alratetakenbytheLevel-1combinedτ-jettriggeroverthatofthesingle-triggersingleτ-jettrigger(~2kHz)isshowninFigure15-63.
Theadditionalratefortheproposedtis0.
83kHz.
Thefullrateforeventsselectedbythecombinedtrigger(bothLevel-1andnd)passingthesingle-,singleτ-jetorcombinedthresholdsis5.
8kHz.
Level-1Triggerefficiencyasthefunc-sforhighluminosity.
τeventstakenbysingle-τtriggerareincluded.
Thediffer-contourlinesrepresentsachangein%.
TheLevel-1cutcorrespondingtothects~70%ofthereferenceevents.
Figure15-63Level-1Triggerrateathighluminosityfromτevents.
ThisrateisinadditiontotheLevel-1single-andLevel-1single-τtriggerrates.
Theaddi-tionalrate,fortheLevel-1cutthatcorrespondstotheofflinecut,is0.
83kHz.
cut[GeV/c]TL1muonp5101520250.
6980.
660.
66effic>70%cut[GeV/c]TL1muonp0510152025cut[GeV]TL1tauE020406080100120140833Hzrate>1Hzrate>3Hzrate>10Hzrate>30Hzrate>100Hzrate>300Hzrate>1kHzrate>3kHzrate>10kHzFigure50.
Level-1Triggerrateathighluminosityfromτevents.
ThisrateisinadditiontotheLevel-1single-andLevel-1single-τtriggerrates.
Theadditionalrate,fortheLevel-1cutthatcorrespondstotheoinecut,is0.
83kHz.
CMSHighLevelTrigger70TheadditionalratetakenbytheLevel-1combined+τ-jettriggeroverthatofthesingle-trigger(6kHz)andsingleτ-jettrigger(2kHz)is0.
83kHzasshowningure50.
Thefullrateforeventsselectedbythecombinedtrigger(bothLevel-1andLevel-1τfound)passingthesingle-,singleτ-jetorcombinedthresholdsis5.
8kHz.
TheHLTanalysispathforthischannelproceedsasfollows:identicationofaLevel-2jetcorrespondingtotheLevel-1τ-jetwithanETrequirementcalorimeterisolationrequirementfortheτLevel-2identicationandpTrequirementcalorimeterisolationrequirementfortheLevel-3identicationandpTrequirementτ-jetidenticationandisolationrequirementinthepixeldetectorisolationrequirementwithfulltracker(orwithpixeldetector)TheresultingHLTecienciesandratesareshowningure51asthefunctionoftheHLTrequirements.
OnlyeventspassingtheproposedLevel-1thresholdsareincluded.
SettingtheHLTthresholdsattheoinevaluespreserves32%ofthebaselinesampleevents.
Thecorrespondingratefromthemuonminimum-biassamplesisabout1Hz.
ThedetailedlistofrejectionfactorsandecienciesforeachHLTstepisgivenintable22forthehighluminositycase.
Thelowluminositycaseissimpler.
TheLevel-1single-thresholdof12GeV/cisbelowtheoinerequirementandthereisnoneedtoallocatebandwidthtothe+τ-jetchannel.
TheLevel-1single-andsingle-τtriggers(ET>93GeV)selectabout72%oftheeventsinthesample.
TheandτidenticationandselectioncriteriaintheHLTreducethiseciencyto39%withabackgroundrateof0.
2Hz.
7.
9.
SummaryofLevel-1andHLTselectionforHiggsChannelswithτ-leptons.
TheLevel-1andHLTpathsusedtotriggerontheMSSMA0/H0andH+Higgsbosonswithmassgreaterthan200GeV/c2are:A0/H0→ττ→2τ-jets.
–Level-1:singleanddoubleτ-jet.
–HLT:calorimeter+trackerisolation.
H+→τν→τjet+E/T.
–Level-1:singleτ-jet.
–HLT:calorimeterE/Tandtrackerisolationontheτ-jet.
A0/H0→ττ→e+τ-jet.
–Level-1:single-eandcombinede+τ-jettriggers.
–HLT:electronselection(section3)andτ-jetisolationwiththetracker.
A0/H0→ττ→+τ-jet.
CMSHighLevelTrigger71342Thelow-luminositycaseissimpler.
TheLevel-1single-thresholdof12GeV/cisbelowtheofflinecutandthereisnoneedtoallocatebandwidthtothe+τ-jetchannel.
TheLevel-1single-andsingle-τtrig-gers(ET>93GeV)selectabout72%oftheeventsinthesample.
TheandτidentificationandselectioncriteriaintheHLTreducethisefficiencyto39%withabackgroundrateof0.
2Hz.
Figure15-64Fullselection(Level-1+HLT)inH→ττ→+τjetchannel.
Theselectionefficiency(left)andcorrespondingbackgroundrate(right)areshown.
TheLevel-1combinedτcutisatLevel-1PT=14GeV/candLevel-1τ-jetET=45GeV.
EventsmustpassLevel-1andallHLTandτselectionrequirements.
Thetau95%efficiencyscaleisusedfortauET.
The90%efficiencyscaleisusedforPT.
Theefficiencyandratefortheofflinethreshold(PT=15GeV/c,ET=40GeV)aremarked.
Table15-22SummaryofLevel-1andHLTselectionefficienciesandbackgroundratesintheH→2τ→+τ-jetchannelforthethresholdscorrespondingtotheofflinecutatPT=15GeV/c,ET=40GeV.
Theefficiencyisdefinedwithrespecttoalleventsintheusefulsample.
EfficiencyRate[Hz]EventspassingLevel-1single,singleτ,orcombinedtrigger0.
705.
8*103EventspassingLevel-1combinedtriggernotselectedbysingle-orsingle-τtrigger0.
04830L2identificationwithETandPTcuts0.
63990L2andcalotauisolation0.
53380L2andmuoncaloisolation0.
61420L2combined0.
51150L3identificationwithPTcut0.
4959L3andtauisolation0.
333.
4L3andmuonisolation0.
4825L3combined0.
321.
2cut[GeV/c]Tmuonp0510152025303540cut[GeV]TtauE01020304050607080900.
32effic>10%effic>20%effic>30%cut[GeV/c]Tmuonp0510152025cut[GeV]TtauE01020304050601.
2Hz22.
7Hzrate>1Hzrate>3Hzrate>10Hz342isgiveninTable15-22.
Thelow-luminositycaseissimpler.
TheLevel-1single-thresholdof12GeV/cisbelowtheofflinecutandthereisnoneedtoallocatebandwidthtothe+τ-jetchannel.
TheLevel-1single-andsingle-τtrig-gers(ET>93GeV)selectabout72%oftheeventsinthesample.
TheandτidentificationandselectioncriteriaintheHLTreducethisefficiencyto39%withabackgroundrateof0.
2Hz.
Figure15-64Fullselection(Level-1+HLT)inH→ττ→+τjetchannel.
Theselectionefficiency(left)andcorrespondingbackgroundrate(right)areshown.
TheLevel-1combinedτcutisatLevel-1PT=14GeV/candLevel-1τ-jetET=45GeV.
EventsmustpassLevel-1andallHLTandτselectionrequirements.
Thetau95%efficiencyscaleisusedfortauET.
The90%efficiencyscaleisusedforPT.
Theefficiencyandratefortheofflinethreshold(PT=15GeV/c,ET=40GeV)aremarked.
Table15-22SummaryofLevel-1andHLTselectionefficienciesandbackgroundratesintheH→2τ→+τ-jetchannelforthethresholdscorrespondingtotheofflinecutatPT=15GeV/c,ET=40GeV.
Theefficiencyisdefinedwithrespecttoalleventsintheusefulsample.
EfficiencyRate[Hz]EventspassingLevel-1single,singleτ,orcombinedtrigger0.
705.
8*103EventspassingLevel-1combinedtriggernotselectedbysingle-orsingle-τtrigger0.
04830L2identificationwithETandPTcuts0.
63990L2andcalotauisolation0.
53380L2andmuoncaloisolation0.
61420L2combined0.
51150L3identificationwithPTcut0.
4959L3andtauisolation0.
333.
4L3andmuonisolation0.
4825L3combined0.
321.
2cut[GeV/c]Tmuonp0510152025303540cut[GeV]TtauE01020304050607080900.
320.
35effic>10%effic>20%effic>30%cut[GeV/c]Tmuonp0510152025cut[GeV]TtauE01020304050601.
2Hzrate>1Hzrate>3Hzrate>10HzFigure51.
Fullselection(Level-1+HLT)inA0/H0→ττ→+τ-jetchannel.
Theselectioneciency(left)andcorrespondingbackgroundrate(right)areshown.
TheLevel-1combinedτrequirementisatLevel-1pT=14GeV/candLevel-1τ-jetET=45GeV.
EventsmustpassLevel-1andallHLTandτselectionrequirements.
Theτ95%eciencyscaleisusedfortheτET.
The90%eciencyscaleisusedforpT.
Theeciencyandratefortheoinethreshold(pT=15GeV/c,ET=40GeV)aremarked.
L=1034cm2s1.
Table22.
SummaryofLevel-1andHLTselectionecienciesandbackgroundratesintheA0/H0→ττ→+τ-jetchannelforthethresholdscorrespondingtooinerequirementofpT=15GeV/candτ-jetET=40GeV.
Theeciencyisdenedwithrespecttothebaselinesample.
EciencyRate[Hz]EventspassingLevel-1singlesingleτ,orcombinedtrigger0.
705.
8*1033EventspassingLevel-1combinedtrigger0.
04830L2identicationwithETandpTrequirements0.
63990L2andcalotauisolation0.
53380L2andmuoncaloisolation0.
61420L2combined0.
51150L3identicationwithpTcut0.
4959L3andtauisolation0.
333.
4L3andmuonisolation0.
4825L3combined(HLT)0.
321.
2notselectedbysingleorsingleτtriggerCMSHighLevelTrigger72Table23.
TheeciencyoftheLevel-1andHLTselections,theHLToutputratesandCPUtimeforlow(high)luminosityfortheMSSMHiggsdecayswithτ-leptonsinthenalstate.
TheCPUtimeisgivenonlyforthelowluminositystudy.
Level-1HLToutputHLTHLTCPUChannel(%)(Hz)(%)(ms)2τ-jet78(62)3(8)45(36)130τ-jet+E/T81(76)1(2)58(53)38+τ-jet72(70)0.
2(1.
2)54(46)660e+τ-jet80(69)0.
4(1.
8)70(71)165–Level-1:single-andcombined+τ-jettriggers.
–HLT:muonselection(section4)andτ-jetisolationwiththecalorimeterandthetracker.
TheHLToutputrates,thesignaleciency(forMH=200GeV/c2)oftheLevel-1andHLTselectionsaswellastheCPUtimeatbothlowandhighluminosityarelistedintable23.
TheeciencyofthecombinedtriggersusedforA/H→ττ→+τ-jetchan-nelsisabout2-5%higherthanthoseofthesingle-leptontriggerandafunctionoftheHiggsmass.
ForHiggsmassesaround120GeV/c2,thecombinedtriggersareexpectedtocontributesignicantlytotheeciencyofthefusionchannelqq→qqH,H→ττ.
8.
Identicationofb-jetsInclusiveb-taggingofjettriggerscanbeusedfortheHLTselectionofphysicschannelswithb-jetsinthenalstate.
Thealgorithmsusedforb-taggingrelyontheb-hadronproperlifetime(cτ450m),whichgivesrisetotrackswithlargeimpactparameterwithrespecttotheproductionvertex.
8.
1.
b-taggingAlgorithmAwiderangeofalgorithmshavebeendevelopedwithinCMStotagb-jets[30].
Thetaggingmethodchosenforthestudiespresentedherereliesonthetrackimpactparameter.
Thetrackimpactparametercanbecalculatedeitherinthetransverseview(2Dimpactparameter)orinthreedimensions(3Dimpactparameter).
Intheformercaseitisnotaectedbytheuncertaintyonthez-componentoftheprimaryvertexpositionwhileinthelattercasealargersetofinformationcanbeused.
Inbothcasesthecalculationisperformedstartingfromthetrajectoryparametersattheinnermostmeasurementpoint.
Inthe2Dimpactparametercasetheestimatecanbedoneanalyticallysincethetrajectoryiscircularinthetransverseview.
Inthethree-dimensionalcasetheCMSHighLevelTrigger73i.
p.
jettracktrackVSQminimumdistancelinearisedFigure52.
Representation(nottoscale)ofthetrackthree-dimensionalimpactparameter.
extrapolationisperformedbyiteration.
Figure52showsthemainingredientsofthethree-dimensionalimpactparametercalculation:rstthepointofclosestapproachofthetracktothejetdirection,S,isfound.
ThispointapproximatesthedecaypointoftheBhadron.
Thetracksarethenlinearizedandtheirthree-dimensionalimpactparameteriscomputedastheminimumdistancefromtheprimaryvertexV.
TheVQsegmentingure52iscalledthedecaylengthandapproximatestheightpathoftheBhadron.
TheimpactparameterissignedaspositiveifQisupstreamofVinthejetdirection(asintheexampleshowningure52),andnegativeotherwise.
ThetracksfromaBdecayshouldhaveapositiveimpactparameter,whilethosecomingfromtheprimaryvertexhaveanimpactparametercomparabletotheexperimentalresolution.
Thetagmakesuseofthetrackimpactparametersignicance,whichisdenedastheratioofthevalueoftheimpactparameterwithitsuncertainty.
Ajetistaggedasab-jetifthereexistaminimumnumberoftrackswithimpactparametersignicanceaboveagiventhreshold.
Inordertospeedupthereconstruction,onlytrackswithinajetconeareused.
Theperformanceoftheb-taggingalgorithm(tagger)dependscruciallyonthequalityofthetracksandthejetdirection.
Tracksresultingfromsecondaryinteractionswiththematerial,K0SandΛ0decaysarereducedbyrequiringthe2Dimpactparameterbelessthan2mmandimposingamaximumonthedecaylengthVQwhichdependsonthejetenergyandrapidityandvariesbetween1.
5to10cm.
Optimizationoftheserequirementswasperformedtomaximizetheb-tagsignaleciencyataxedmis-taggingrateof1%.
8.
2.
TaggingregionTracksarereconstructedinaconearoundtheLevel-1calorimeterjet.
Theconeapexistakenasthepixelreconstructedprimaryvertexwiththealgorithmpresentedin[32].
TheoptimalconewidthdependsonthereconstructedjetET.
Thenumberoftracksfromb-decaysinsidethejetconeislargelyafunctionoftheconesize.
Thefractionoftrackscomingfromb-decaysreachesaplateauvalue[31]ataR0.
25.
Beyondthispointonlytracksfromthehadronizationprocessareadded.
Inthecaseoflightavourjetsthenumberoftracksincreasesalmostlinearly.
Athighluminositytheratioofnon-btrackstob-tracksincreases,requiringaharderpTcut.
CMSHighLevelTrigger74Figure53.
Eciencyofthepixelalgorithmtocorrectlydeterminetheprimaryvertexoftheeventwithin100,300and500m,athighluminosity,asafunctionoftheminimumpTcutonthepixellines.
TheprimaryvertexistakenasthevertexhavingassociatedtoitpixellineswiththelargestsummedpT.
Atlowluminositythealgorithmhashigheciency.
AthighluminositythealgorithmismodiedsothatonlypixellinesaboveahighpTthresholdareused.
Thehigheciencyismaintainedwithasmalllossofprecision.
Figure53showstheeciencyofthepixelalgorithmtocorrectlyassigntheprimaryvertexwithin100,300and500m,athighluminosity,asafunctionoftheminimumpTcutonthepixellines.
Primaryvertexreconstructionrequiresabout50msecona1GHzPentium-IIICPUforboththelowandhighluminositycases.
8.
3.
TrackReconstructionTrackreconstructionisbasedonthepartialreconstructionoftracksusingtheregionalapproach(sectionAppendixA):startingfrompixelseeds,additionalhitscompatiblewiththetrackpT,aresoughtinaregionaroundthejetaxis.
Thereconstructionisstoppedafteranadequatenumberofhitsisfoundalongthetrajectory.
Twodierentregionalseedingalgorithmshavebeenstudied.
Therst(referredtoas"pixelselectiveseeds")usesthepixellinesfoundbythepixelreconstructionwhicharecontainedinsideaconeofR1.
5.
ForjetsattheETrange802.
0.
ForjetswithET>150GeV:twotrackswiths>2.
5.
Atlowluminosityrunningconditionssuchaselectionis55%ecientforb-jetswithabackgroundrejectionfactorofabout10,almostindependentofthejetET.
Itcorrespondstoarateof5HzforacutontheleadingjetETofabout200GeVor160GeVonthenext-to-leadingjet.
ThisselectioncanbeusedinthecaseofSUSYsearches,wherethenumberofb-jetsinthenalstateislarge(section9).
9.
HLTSelectionandPerformanceOverviewThissectionsummarizesthephysicsobjectselection,thetotalestimatefortheCPUrequirements,andthephysicsperformanceofaprototypeHLTtableforthestart–upluminosityof2*1033cm2s1.
Thecurrentsetofthresholdsandratestostorageforeachphysicsobject,describedintheprecedingsections,islistedintable24.
Thevaluesofthethresholdsshownintable24areindicativeofthetypeofeventmixturethatwouldyieldanoutputeventrateofO(100)Hz.
TheCMSstart–upHLTallocatedtotalrateis150Hztoallowfor(i)triggercontingency(additionalphysicsandback–uptriggers)andconsequently(ii)meetingthegoalsofarichphysicsprogram.
A1.
5MB/eventimposesarequirementonthedatarecordingrateof225MB/s.
9.
1.
CPURequirementAkeyissuefortheHLTistheCPUpowerrequiredfortheexecutionofthephysicsobjectsselectionalgorithms.
ThealgorithmsweretimedonaPentium-III1GHzprocessor,andtherequirementsvariedfrom50msforjetreconstruction,to700msformuonreconstruction.
TherststepistoweighttheCPUneedsofthealgorithmsbythefrequencyoftheirapplication,whichistheLevel-1triggerrateofthecorrespondingchannels.
Thisisshownintable25andyieldsatotalof4092CPUsecondsasthetotalneedtocoverthe15.
1kHzofeventsoutputfromtheLevel-1triggerforlowluminosityconditions.
InthefullLevel-1triggerratebudgetoftable2thereisanadditional0.
9kHzofminimumbiaseventsthatwillbeusedforcalibrationandmonitoring.
TheseeventsareassumedtorequirethesameamountofCPUasthemeanofthe15kHzofeventsforwhichCPUtimeestimatesareavailable.
TheaverageprocessingtimepereventatLevel-1is271ms.
CMSHighLevelTrigger80Table24.
High-LevelTriggerrequirementsatlowluminosity.
ThethresholdscorrespondtothevaluesinETorpTwith95%eciency(90%eciencyformuons).
ThereisnoactualthresholdintheHLTselectionforτ-jets,sothethresholdshownisthatofthecorrespondingLevel-1Triggerrequirement.
()Calibrationpercentageallocatedcorrespondstowellunderstooddetectorperformance.
Atstart-up,thiscanbeashighas30%ofthetotalrate.
TriggerThresholdRateCumulativeRate(GeVorGeV/c)(Hz)(Hz)inclusiveelectron293333di-electron17134inclusivephoton80438di-photon40,25543inclusivemuon192568di-muon7472τ-jet*E/T86*65173di-τ-jets593761-jet*E/T180*1235811-jetOR3-jetsOR4-jets657,247,113989electron*τ-jet19*450.
489.
4muon*τ-jet15*400.
289.
6inclusiveb-jet237594.
6calibrationandotherevents(10%)10105TOTAL105Table25.
SummaryofCPUtimerequiredfortheselectionofeachphysicsobjectsintheHLT.
TheCPUguresrefertoa1GHzIntelPentium-IIICPU.
PhysicsObjectCPUtimeperLevel-1Level-1TriggerrateTotalCPUtimeevent(ms)(kHz)(s)electron/photon1604.
3688muon7103.
62556tau1303.
0390jetsandE/T503.
4170electron+jet1650.
8132b-jets3000.
5150CMSHighLevelTrigger81WeestimatetheCPUpowertocarryoutthephysicsprogramatthestart-upoftheLHC,whentheluminositywillnothavereacheditsfullvalue.
ThecurrentscenarioforCMSistoprovideaDAQsystemcapableofreadingamaximumof50kHzofeventsacceptedbytheLevel-1Trigger.
TheCPUrequirementforthissystemis15,000CPUsasinthoseavailableinastandardcommercialPersonalComputer(PC).
Sincethesetimingmeasurementsin2002thepowerperCPUhasbeenincreasedbyafactor3-3.
5soin2005thiscorrespondstoabout4500-5000CPUs.
Toextrapolatetheseguresfromearly2005totheyear2007thebasicthesisofMoore'sLaw,i.
e.
thatCPUpowerincreasesbyafactortwoevery1.
5years,isused.
Thisimpliesthatatotalof2,000CPUswillbeneededforthesystemattheLHCstart-up.
9.
2.
EciencyoftheHLTselectionforMajorPhysicsChannelsThediscoveryofthelong-soughtHiggsbosonisthefocusofthephysicsprogramoftheLHC.
ThissectionsummarizesthestudiesofsomeoftheexpectedHiggssignals,bothwithinthestandardmodelandinthecontextofsupersymmetry.
ThemassrangetodiscoverthestandardmodelHiggsattheLHCrangesfromtheupperlimitofdirectsearchesatLEP,namely114.
4GeV/c2toapproximately1TeV/c2.
Intheheavymassrange(upto800GeV/c2)thechannelswiththebestsensitivityfortheHiggsistheH→ZZ.
InparticulartheH→ZZ→fourleptons,e.
g.
channelisreferredtoasthe"gold-plated"one,formassesabove180GeV/c2.
ForlowervaluesoftheHiggsmassthedecaychannelsH→WW→llνν,H→γγ,WH→Wγγ,qqH→qqWW,andqqH→qqττbecomeimportantfortheHiggsstudy.
ThechannelsttH→ttγγ,andttH→ttbbcanalsobeexploredtodiscoverandstudytheHiggs.
Fortheregionaround120GeV/c2themostpromisingchannelstodatearethefusionprocessesorthedecaysintotwophotons.
ThedecayH→γγwillbetriggeredattheHLTrequiringtwophotonsdetectedintheECALandvalidatedbythetracker,usingtheasymmetriccutsofET>40and25GeVforthephotons.
Thisrequirementpersistsinthenaloineselectionforthischannel.
Ityieldsanalbackgroundratetotapeof5Hz.
Forlow-luminosityrunningthecombinedLevel-1/HLTtriggereciencyforaHiggswithmassof115GeV/c2is77%forallthedecayswherebothphotonsarewithintheECALducialvolume(|η|30GeV)intheqq→qqHprocessnojetsinHFonejetinHF2jetsinHFnocuton|ηj1ηj2|49%45%6%|ηj1ηj2|>4.
422%65%13%(i)EjT>40GeV,|ηj|4.
4,ηj1ηj2100GeV(iii)Mjj>1200GeV/c2(iv)φjj30GeVforeachjetisshownintable26beforeandafterthecutontherapiditygapbetweenthejets.
Aftertherapiditygapconstraint,almost80%oftheHiggseventswillhaveatleastonetaggingjetintheHF.
TheLevel-1jettriggercoverstheentirecalorimeteracceptance,includingtheHFcalorimeter.
AtLevel-1ajet+E/TtriggercanthereforebeusedfortheinvisibleHiggsselection.
Figure59showsthetransverseenergyofthehighestETjet(left)andcalorimeterE/T(right)reconstructedattheHLTandatLevel-1atL=1034cm2s1forHiggseventspassingtheWBFrequirementsandforaHiggsmassof120GeV/c2.
TheLevel-1triggerwasoptimizedbyexaminingthetriggerrateforasinglejetplusE/TtriggerversusthesignaleciencybychangingtheE/Tthresholdsforthexedsetofsinglejetthresholds.
Figure60showstheLevel-1jet+E/TtriggerrateandHiggseciencyforsinglejetthresholdsof70(60),90(70),110(80)athigh(low)luminositywhentheE/Tthresholdisvaried.
Table27liststheLevel-1jet+E/TtriggerthresholdsandtheHiggseciencyforLevel-1jet+E/Ttriggerratesof0.
2,0.
5and1.
0kHzatlowandhighluminosity.
Arateof0.
5kHzgivesahighHiggseciency,namely98%(80%)forlow(high)luminosity.
FortheHLTselection,theoinerequirementsEjT>40GeV,|ηj|4.
4areusedalongwiththerequirementofMjj>1TeV/c2,andaE/Trequirement.
Figure61(leftplot)displaystherateforQCDmulti-jeteventsasafunctionoftheE/TthresholdwithonlytheETandηrequirementsappliedandwiththeadditionalMjjrequirementalsoapplied.
Arateof0.
1HzcanbereachedatlowluminosityforE/T>110GeVwithouttheMjjcut.
Thesignaleciencyinthiscaseiscloseto100%sincetheoinecutonE/Tis100GeV(gure59).
Athighluminosityarateof0.
2HzcanbereachedwiththeMjjcutandan150GeVthresholdonE/T.
ThetotalLevel-1jet+E/TandHLTeciencyforHiggsathighluminosityisshowningure61(rightplot)asafunctionoftheE/Tcuto.
For0.
2Hzrate(E/T>150GeVandMjj>1TeV/c2)theCMSHighLevelTrigger84Figure59.
Higgseventsintheprocessqq→qqH,withtheHiggsdecayinginvisibly(MH=120GeV/c2),thatsatisfytheWBFrequirements.
(Left)Transverseenergyofthehighest-ETjetreconstructedinoine(solidhistogram)andatLevel-1(dashedhistogram).
(Right)E/Treconstructedoine(solidhistogram)andatLevel-1(dashedhistogram).
(for).
0102030405060708090100050100150200250300350400ETjetatLevel-1andHLT,GeVnev/20GeVqq→qqH,H(120GeV)→invpassedWBFselectionssolid-1stHLTjetdotted-2ndHLTjetdashed-1stLevel-1jetL=1034cm-2s-101020304050607080050100150200250300350400ETmissatLevel-1andHLT,GeVnev/20GeVL=1034cm-2s-1qq→qqH,H(120GeV)→invpassedWBFselectionssolid-HLTETmissdashed-Level-1ETmissFigure60.
QCD2-jetrate(inkHz)forajet+EmissTtriggerversuseciencyforqq→qqH,withtheHiggsdecayinginvisibly,foraHiggsmassofMH=120GeV/c2,andforeventswhichsatisfytheWBFselectionwhentheE/Tthresholdisvariedandwithsinglejetthresholdsaslabeled,low(left)andhigh(right)luminosity.
0.
70.
750.
80.
850.
90.
95110-210-11Level-1Jet+METRate(kHz)εLevel-1foroff-lineqq→qqH,H→inv(%)J>60GeVJ>70GeVJ>80GeVMH=120GeVL=2x1033cm-2s-10.
40.
50.
60.
70.
80.
9110-1110Level-1Jet+METRate(kHz)εLevel-1foroff-lineqq→qqH,H→inv(%)J>70GeVJ>90GeVJ>110GeVMH=120GeVL=1034cm-2s-1CMSHighLevelTrigger85Table27.
Summaryofthesingle-jetplusE/TLevel-1triggerthresholdsforatotaltriggerrateof0.
2,0.
5,and1.
0kHzatlowandhighluminosity.
ShownarethejetandE/Tthresholds,theeciencyforqq→qqHwiththeHiggs(MH=120GeV/c2)decayinginvisiblyforeventswhichpasstheWBFcuts.
RateforLevel-1jet+E/Ttrigger0.
2kHz0.
5kHz1.
0kHzlowluminositysingle-jetthreshold606060E/Tthreshold(GeV)736456eciency0.
960.
980.
99highluminositysingle-jetthreshold,707070E/Tthreshold(GeV)12211273eciency0.
720.
790.
84Figure61.
Left:QCD2-jetbackgroundrateaftertopologicalWBFrequirementsasafunc-tionoftheE/TcutoforL=1034cm2s1(solidhistogram)andL=2*1033cm2s1(dashedhistogram).
Right:totalLevel-1singlejetplusE/TandHLTeciencyforqq→qqH,withtheHiggsdecayinginvisibly,MH=120GeV/c2,andforeventswhichpassedWBFcuts,asafunctionofE/TcutoforL=1034cm2s1.
10-210-1110102103104105106050100150200250300HLTETmisscutoff(GeV)Rate(Hz)HLTselectionsofqq→qqH,H→invsolid-L=1034cm-2s-1dashed-L=2x1033cm-2s-1aftercuts:ETJ>40GeV,|η|4.
2ηJ1*ηJ21TeV00.
20.
40.
60.
81050100150200250300cutoffonHLTETmiss(GeV)ε(qq→qqH,H→inv)(%)L=1034cm-2s-1εofLevel-1J(70)+MET(112)andHLTETmissforH→inv.
,MH=120GeVpassedWBFcutsWBFcuts:ETJ>40GeV,|η|4.
4ηJ1*ηJ21200GeVφJ1J2100GeVHiggseciencyis0.
7.
9.
3.
SupersymmetrySearchesOneofthemaingoalsoftheLHCistosearchforevidenceforsupersymmetry(SUSY),themostpowerfulextensionofthestandardmodel.
IfSUSYexists,largeamountsofsupersymmetricparticles(sparticle)areexpectedtobeproducedshortlyaftertheLHCturn-on.
However,unlessSUSYisdiscoveredattheTevatronbeforetheLHCstart-up,thesignatureofSUSYwillnotbeknowninadvance.
ThemostpopularSUSYmodelsCMSHighLevelTrigger86Table28.
ParametersusedforthegenerationoftheSUSYmSUGRAsamplesusedinthispaper.
ForallpointsA0=0,tanβ=10,and>0.
MassesareinGeV/c2andcrosssectioninpb.
PointM0M1/2σmgmuLmχ01Mh42019018146641070110515018021344741566110630015050034940645106725010500.
0172235198644512289009300.
02220321962391121915007000.
05916251975293120invoketheconservationofR-parity(RP),whichmakesthelightestSupersymmetricparticlestableandinsomecasesanexcellentcandidateforcolddarkmatter.
Inthesemodels,squarkandgluinoevents,whichareproducedstronglyandthereforehaveverylargeproductioncrosssection,wouldappearinthedetectoraseventswithmultiplejetsandlargeE/T.
Duetocascadedecaysofcharginosandneutralinosthenalstateusuallyalsocontainsanumberofleptons.
Insomepointsoftheparameterspacethedirectcharginoneutralinoproductionprovidesstrikingtri-leptonsignatures.
Supersymmetrymodelshavealargenumberoffreeparameters.
TherehavebeenseveralstudiestoidentifypointsintheSUSYparameterspacethatwillinsomewayspantherangeofsignaturesandpredictionsthatapplytothestartoftheLHC.
Reference[41]wasusedtoselectthepointsstudiedhere.
ThesepointsallusethemSUGRAparametrizationoftheSUSYparameterspace.
Otherparametrizationshavenotbeenconsidered,sincethepurposeofthisstudyisnottoprovideanexhaustivestudyofSUSYbuttogiveexamplesoftheprototypeLevel-1anfHLTselectioneciencyforsupersymmetricsignatures.
Atlowluminosity,thegreatestchallengecomesfromthepointswiththelowestsparticlemassesjustabovethereachoftheTevatron,becausethetransverseenergiesofthejetsandE/Tarerelativelylow.
Athighluminosity,thechallengeistomaximizetheacceptanceforthehighestmasspoints,sincetheyhavethesmallestcrosssection.
Table28liststheparametersandthemassesofsomesparticlesaswellastheproductioncrosssectionsforthepointsusedtoexerciseandtesttheappropriateHLTselectionpaths.
TheSUSYmassspectraandbranchingratioswerecalculatedusingISAJET7.
51[42].
ThisinformationwasimportedintoHERWIG6.
301[43],whichwasusedtogeneratethesamples.
ThepointswerechosentogiveavarietyofpotentialSUSYsignatures.
Point4hasenhancedslepton(especiallystau)production.
Point5isa"typical"SUSYpointwithsquarkslighterthangluinosresultinginlargeE/T.
Atpoint6thegluinosarelighterthanthesquarksresultinginlargejetmultiplicitynalstateswithasmallerE/Tthanatypicalpoint.
Atpoint7stauandsneutrinoproductionisCMSHighLevelTrigger87Figure62.
HLTrateversuseciencyforSUSYsignals,foreventsthatpasstheLevel-1jet+E/Ttrigger.
(Left)HLTrate-eciencycontoursforeachpointandforarangeofjetthresholdsusingthe4-jettriggerpath.
(Right)HLTrate-eciencycontoursforeachpointandforarangeofE/Tthresholdsusingthejet+E/Ttriggerpath.
11010210300.
10.
20.
30.
40.
50.
60.
70.
80.
916.
8HzSUSYSignalEfficiencyRate(Hz)qPoint4sPoint5vPoint6Point4RPoint5RPoint6R11010210300.
10.
20.
30.
40.
50.
60.
70.
80.
915.
1HzSUSYSignalEfficiencyRate(Hz)qPoint4sPoint5vPoint6Point4RPoint5RPoint6Renhanced.
Point8ischaracterizedbyanenhancedb-jetyieldcomparedtopoint7,duetoneutralinodecaystohiggswhiletheE/Tissimilartothatofpoint7.
Forpoint9,thegluinosarelighterthanallsquarks,exceptforthelighterstop,thusallowingthedecayofgluinotothelighteststopwhichdominatesandthereforeeventshavemanyjetsandsmallerE/T.
Whiletheseexactpoints(points4,5,and6inparticular)maybeexcludedbyLEPHiggssearches,HiggsproductionandtheexactmassfortheHiggsinthedecaysdoesnotplayanimportantroleintheobservabilityorthecharacteristicsoftheseevents.
ThesamepointsareusedtosimulateSUSYwithR-parityviolationwithχ01→jjj.
Forthelow-masspoints,simpletriggerswithjetsandE/Twereconsidered.
Atlowluminositya3-jettriggerandajet+E/TtriggerareconsideredatLevel-1.
FortheHLT,thejet+E/Tandthe4-jetchannelareconsidered.
Figure62(left)showsthe4-jetHLTtriggerrateversusthesignaleciencyforeventsthatpasstheLevel-1jet+E/TtriggerforthesixSUSYpointsasthethresholdontheleadingjetisvaried.
Figure62(right)showstherateversuseciencyforthejet+E/TtriggerasthethresholdontheE/Tisvaried.
Thearrowsontheplotsindicatethethresholdschosenforthelowluminositytriggertableasacompromisebetweeneciencyandbandwidth.
Table29summarizestheLevel-1andHLTthresholdsvalues,thetriggerratesandsignalecienciesforasetofpointsandforlowluminosityrunning.
Points4R,5Rand6RarethecorrespondingR-parityviolatingones.
TheHLTecienciesshownarewithrespecttoeventsthatpasstheLevel-1trigger.
Aftertherstfewruns,andoncetheactualtriggerconditionsareknown,moretriggerswillbeaddedtoincreasetheeciencyforSUSYsignals.
Forthehighluminositycase,thehighmassSUSYpoints7,8,and9areconsidered(asCMSHighLevelTrigger88Table29.
TheLevel-1andHLTthresholds,ratesandecienciesforsixsupersymmetrypointsatlowluminosity.
TheHLTecienciesarewithrespecttoeventsthatpasstheLevel-1trigger.
Allthresholdsrefertothevalueswith95%eciency,withtheexceptionoftheLevel-1E/Twhichistheactualthresholdvalue.
ForadenitionoftheSUSYpoints,seetext.
Level-1TriggerHigh-LevelTriggerSUSYpoint1jet>88GeV+1jet>180GeV+E/T>46GeV3jets,ET>86GeVE/T>123GeV4jets,ET>113GeVeciency(%)eciency(%)eciency(%)eciency(%)(cumulative)(cumulative)48860(92)6711(69)58764(92)6514(68)67168(85)3716(44)4R6789(94)2728(46)5R5890(93)1730(41)6R4784(87)920(26)Backgroundrate(kHz)rate(kHz)rate(Hz)rate(Hz)(cumulativerate)(cumulativerate)2.
30.
98(3.
1)5.
1Hz6.
8(11.
8)Table30.
TheLevel-1andHigh-LevelTriggerthresholdvalues,ratesandecienciesforsixsupersymmetrypointsathighluminosity.
TheHLTecienciesarewithrespecttoeventsthatpasstheLevel-1Trigger.
Allthresholdsrefertothevalueswith95%eciency,withtheexceptionoftheLevel-1E/Twhichistheactualcutvalue.
ForadenitionoftheSUSYpoints,seetext.
Level-1TriggerHigh-LevelTriggerSUSYpoint1Jet>113GeV+3jets,ET>111GeVE/T>239GeV4Jets,ET>185GeVE/T>70GeVeciency(%)eciency(%)eciency(%)eciency(%)(cumulative)(cumulative)79062(90)8518(85)89776(98)9028(92)99167(94)7228(76)7R9199(100)7075(90)8R86100(100)5878(88)9R7599(100)4152(64)Backgroundrate(kHz)rate(kHz)rate(Hz)rate(Hz)(cumulativerate)(cumulativerate)4.
51.
1(5.
4)1.
61.
5(3.
0)CMSHighLevelTrigger89Table31.
Expectedmasslimitsonnewparticlesthatdecaytodi-jetsatLHCturn-on[45]ParticleLimitfor2fb1Limitfor100fb1(GeV/c2)(GeV/c2)W720920Z720940E6di-quarks570780Axigluons11601300excitedquarks9101180wellasthecorrespondingR-parityviolatingones).
Itisstraightforwardtodesignhighlyecienttriggersforthesesamples.
Table30summarizestheoptimizedLevel-1andHLTrequirementsandoutputrates.
TheLevel-1triggerusedarethesinglejet+E/Tanda3-jettrigger,whiletheHLTusesaE/Tanda4-jetselection.
9.
4.
OtherNewParticleSearchesManyscenariosofnewphysics,suchastechnicolour,"LittleHiggs"models[44],andgranduniedtheories,predictnewparticlesthatdecaytotwojets.
Table31listssomeoftheexpectedlimitsonvariousparticlesatLHCturn-on[45].
Becausethecontributiontothemeasuredwidthofadi-jetresonancefromthecalorimeterresolutionislargecomparedtotheintrinsicwidthofmostofthesenewparticles,theresultsfordierentparticlesscaleaccordingtotheirproductioncrosssections.
ThesearchfortheZisusedasanexamplehere.
Theresultsforotherparticlescanbeestimatedbyscalingtheseresults.
Thesearchforlow-massdi-jetresonancesattheLHCwillbechallengingduetothelargebackgroundsfromstandardmodelprocesses.
Signicantamountsofdatabelowtheresonancewillbeneededtobettedtoobtainthefreeparametersintheansatz.
Averyapproximateestimatefortheluminosityneededfora5σdiscoverycanbeobtainedbyestimatingthenumberofeventsduetothesignalinawindowwithawidth±2σoftheGaussianpartoftheresonanceanddemandinga5σexcess.
Thisyieldsalowerlimitontherequiredluminositybecauseitdoesnottakeintoaccountsystematicuncertaintiesandtheproblemofttingforthefreeparameters.
Theresultsarelistedinthesecondcolumnoftable32.
TheanalysisassumesthatdatawillbeneededdowntoanETcutoofatleastatM/4.
Asanexample,thediscoveryofaZwithmass600GeV/c2,willrequiredatadowntoanETcutoof150GeV.
Table32liststherateatET=M/4,theprescalingfactorandresultingratethatwouldbeneededtodiscoverthisparticlein1yearoflowluminosityrunning(20fb1),andin5yearsoflowluminosityrunning(100fb1).
OnecanalsoconsiderthetimeittakestodiscovertheZasafunctionoftheZmassforaconstantratetostorage.
TheinstantaneousluminosityinLHCisexpectedtoCMSHighLevelTrigger90Table32.
MinimumrequirementstodiscoveraZdecayingtotwojets.
Listedare:theintegratedluminosityneededtohavea5σZsignal,thethresholdonthejettriggerETusedtodeterminetheluminosity,therateforthesinglejettriggeratthatthreshold,therateneededtoacquiretheeventswithin1year(20fb1)(andalso,inparenthesis,theprescalefactorrequiredandthenumberofevents),andtherateandprescaletoacquirethatnumberofeventsin5years.
ZmassLuminosityM/4rateraterate(prescale)(events)(prescale)1year5years(TeV/c2)fb1GeVHzHzHz0.
61.
415080056(14.
2)(40·106)11(71)0.
82.
320020023(8.
7)(26·106)4.
5(443)1.
04.
32505512(4.
7)(26·106)2.
3(24)1.
27.
3300259(2.
7)(33·106)1.
9(13)1.
414350117.
8(1.
4)(55·106)1.
6(7)1.
62040066(1)(60·106)1.
2(5)1.
8314503.
5-1.
1(3.
2)2.
0525002-1.
1(1.
9)haveanexponentialdecay,andthereforetheratesatagiventhresholdalsodecreaseexponentially.
Applyingthismodel,andusingdynamicprescalingtokeeptheratetostorageconstant,theprescalingfactoralsodecreasesexponentiallywithtime.
Furthermore,onecanassumeseveraldynamicprescalescenariosanexponentialluminositydecaywithtimeconstantof10hours,duringabeamllof10hours,andaxedratetostorageforthesinglejettriggerof20Hz;axedprescale,witharatetotapeforthesinglejettriggerof20HzatL=2*1033cm2s1;anexponentialluminositydecaywitha10-hourlifetime,duringabeamllof10hours,axedratetostorageforalltriggersof100Hz,takinganinitialrateforthesingle-jettriggersof5Hz.
Allthreescenariosassume20fb1peryearforlowluminosityrunning.
Figure63showsthetimetodiscoveryforthesethreeoptions.
FurthertopicsofnewphysicsincludeforexampleextradimensionsandlittleHiggsmodels.
Ingeneralmassiveobjectsareproducedinthesescenarios,forwhichtheCMStriggercanperformeciently.
Afewexamplesaregivenforillustration.
Extradimensionsmaybeanexplanation,viageometry,forthelargedisparitybetweentheelectroweakandPlanckscaleaswellastheavourstructureweobserveinthestandardmodel.
Theenergyscalewheretheextradimensionsoperateisnottheoreticallyknown.
ThemostlikelyscaleistheGUT/Planckscalearound1015-1019GeV.
Thereisnostrongexperimentalconstraintstodate,thatexcludestheexistenceCMSHighLevelTrigger91Figure63.
Timeofobtaining5σsignicanceoverthebackgroundforthe3prescaleschemesdescribedinthetextasafunctionoftheZmass.
Zprimemass(TeV)0.
60.
811.
21.
41.
61.
822.
22.
4time(years)00.
511.
522.
533.
54dynamicprescaleto20Hzfordijetsfixedprescale,20Hzinitialratedynamicprescaleto100HztotaloflargeextradimensionsthathaveaneectinthephysicsattheTeVscale.
Examplesofsignaturesofextradimensionswithinthemostpopularmodelsare:qq,gg→gG,ZG,γG(ADDmodels),whereGisthegravitonthatescapesdetection.
ThesesignaturesimplythepresenceofmissingETinthenalstateasinthecaseofsupersymmetryeventsinassociationwithajetoraboson.
ForthemostpromisingchannelthesignalmaybecomevisibleoverthestandardmodelbackgroundsforE/Tvaluesof500GeV[47].
TheseeventscanbeecientlytriggeredatLevel-1usingthesinglejetplusE/T,orthesingleleptontriggers.
qq,gg→G→WW,ZZ,γγ(ADDandRSmodels).
Thesesignaturesuseisolatedphotons,electronsandmuonsandsometimesjetsfromweakbosondecays.
ForADDmodelsthereisacontinuumofgravitonmassstatesoverthewholeenergyrange,whileincaseoftheRSmodelsaseriesofresonancesisexpectedwiththerstoneintheTeVmassrange.
Themassiveresonanceswillbeeasilytriggeredbytheleptonandjettriggers.
qq,gg→γ1/Z1,G,ee,,jet-jet;qq→W→lν(ADD,RSandTeV1models).
ExceptfortheADDcaseagainoneexpectsresonanceswithmasseslargerthanabout1TeV.
Thenalstateswithleptonscanbetriggeredwithhigheciencybytheleptontriggers.
FortheADDtwofermionnalstates,thedi-jetoneisleastecientandhasthesameacceptanceasdiscussedforthedi-jetZtriggerabove.
InUniversalExtraDimensionsmodels[48],theKaluza-Klein(KK)particlespectraresemblethesupersymmetricspectra,withthespecialcharacteristicthatingeneralthemassdierencesbetweentheKKparticlestatesaresmall,leadingtojetsandleptonsproducedindecayswithrelativelysmallET,typicallyoftheorderCMSHighLevelTrigger92ofafewtensofGeV.
InmodelvariationsthatinvokeKK-parityviolation[49],spectacularsignatureswithdi-leptons,di-photonsanddi-jetsplusmissingenergybecomeimportant.
Thesecanberetainedusingthesingleordoublelepton/photontriggersaswellasthejetplusE/Ttriggers.
WithinLittleHiggsmodels,newparticlescanbeexpectedintheTeVrangesuchasheavytopquarksTandnewgaugebosons.
TheTquarkswilldecayviachannelssuchasT→Zt→ZWb;T→Wb;T→ht→hWb.
ThenewgaugebosonsAH,ZHandWHcandecayinleptonsortheSMgaugebosons.
Mostanalyses[50]useleptonchannelseitherfromtheW'sinthedecaysoftheT,orstandardmodelgaugebosons,withETcutsoftypicallyO(100)forleptonsproducedwith|η|1.
479)twoECALtriggertowerscorrespondtooneHCALphysicaltowerinφ.
InthisregiontheHCALenergyofonetowerisequallydividedbetweenthetwoECALtriggertowersthatcorrespondtoit.
Inthebarrel-endcaptransitionregion,barrelandendcapsegmentsaresummedtogether.
Thetriggersegmentationoftheforwardhadroncalorimeter(HF)doesnothaveneφbinningbecausethisdetectordoesnotparticipateintheelectronorphotontriggers.
Howeverthecoverageneedstobeseamlessforthejetandmissingenergytriggers.
Thesegmentationintheforwardregionmatchestheboundariesofthe4*4triggerregionsintherestofthecalorimetry.
TheresultingHFtriggertowersegmentationof4η*18φisusedinthejetandmissingenergytriggers.
Theφbinsareexactly20(4*0.
087)andtheηdivisionsareapproximatelythesizeoftheoutendcapdivisions.
Thejettriggerextendsseamlesslyto|η|=5.
Themissingtransverseenergyiscomputedusing20divisionsfortheentireη,φplane.
Thetriggertowersareorganizedincalorimeterregions,eachoneformedby4*4triggerCMSHighLevelTrigger95η=2.
1720η=2.
0430η=1.
8300η=1.
7400η=1.
6530η=1.
5660η=1.
4790η=1.
3920η=1.
3050η=1.
2180η=1.
1310η=1.
0440η=0.
9570η=0.
8700η=0.
7830η=0.
6090η=0.
6950η=0.
5220η=0.
4350η=0.
3480η=0.
2610η=0.
1740η=0.
0870η=0.
0000Mastab/m01.
00.
54.
332m5.
680m2.
935m3.
900m1.
290m1.
811m2.
900m12345678910121314151617181920212223272811EB/1242526η=3.
0000η=2.
6500η=2.
5000η=2.
3220η=1.
9300TrackerEE/1HE/1HB/1FigureA1.
LayoutofthecalorimetertriggertowersintherzprojectionCalorimeterRegion4x4triggertowers,η.
φ=.
35x.
35TriggerTower5x5crystals,η.
φ=.
087x.
087Strip1x5crystals,η.
φ=.
017x.
0871234567891011121314151617η=0.
η=1.
48φ=0.
35ECALHalf-BarrelSupermoduleFigureA2.
CalorimetertriggertowerlayoutinoneECALhalf-barrelsupermodule.
Thetriggertowersareorganizedincalorimeterregionsof4*4towers.
towers.
EachoftheHFtowersistreatedas4*4regionsinceitissegmentedin20φbins.
Thecalorimeter4*4regionsarethebasisofthejetandenergytriggers.
TheηφindexesofthecalorimeterregionsareusedtoidentifythelocationofL1calorimetertriggerobjects(electron/photonsandjets)intheupperstagesofthetriggerchain.
Thetransverseenergysumiscomputedforeachcalorimetertriggertower.
TheECALtriggercellETisthesumoftheETof5*5crystalsinthebarrelandavariablenumberofcrystalsintheendcap.
TheHCALtriggercellETisthesumoftheETofthelongitudinalcompartmentsoftheinnerhadroncalorimeter.
ForeveryECALtriggertowertheinformationthatreectsthelateralextensionoftheelectromagneticshower(referredtoas"FineGrain"orFGvetobit)isusedtoimprovetherejectionofbackgroundintheelectrontrigger.
TheFGvetobitisactivewhenthehighestenergyadjacentstrippairhaslessthanaprogrammablefractionR(typically90%)ofthetowerenergy.
Electronsandphotons(convertedornon-converted),inthepresenceofnoiseandhighluminositypileup,haveRThresholdHitMaxCandidateEnergy:0.
0175ηφηHit0.
087η0.
087φMax0.
0175φHadEMFigureA3.
Electron/photontriggeralgorithm.
notsensitivetominimumionizingparticleenergydepositintheHCAL.
ThenegrainbitisusedtoidentifyminimumionizingparticlesrequiringtheHCALtowerenergytobeinsideaprogrammableenergyrange.
ThedataistransmittedtotheRegionalCalorimeterTrigger(RCT),whichndscandidateelectrons,photons,taus,andjets.
TheRCTseparatelyndsbothisolatedandnon-isolatedelectron/photoncandidatesandtransmitsthemalongwithsumsoftransverseenergytotheGlobalCalorimeterTrigger(GCT).
TheGCTsortsbyETthecandidateelectrons,photons,taus,andjetsandforwardsthetopfourofeachtypetotheglobaltrigger.
TheGCTalsocalculatesthetotaltransverseenergyandtotalmissingenergyvector.
Ittransmitsthisinformationtotheglobaltrigger.
TheRCTtransmitsan(η,φ)gridof"quiet"regionstotheglobalmuontriggerformuonisolationcuts.
AppendixA.
2.
Level-1ElectronandPhotonTriggersTheelectron/photontriggerusesa3*3triggertowerslidingwindowtechniquewhichspansthecompleteη,φcoverageoftheCMSelectromagneticcalorimeter.
Twoindependentstreamsareconsidered,non-isolatedandisolatedelectrons/photons.
Theisolatedstreamrequireselectromagneticandhadronicenergyisolationcriteria.
Theimplementationoflongitudinalandlateralshowerproleselectioncuts,aswellaselectromagneticandhadronicisolationprogrammablecriteriaprovidessafetyandexibilityforthecalorimeterelectron/photontrigger.
Anoverviewoftheelectron/photonisolationalgorithmisshowningureA3.
Thisalgorithminvolvestheeightnearesttriggertowerneighborsaroundthecentralhittriggertowerandisappliedovertheentire(η,φ)plane.
Theelectron/photoncandidateETisdeterminedasfollows:TheETofthe"hittriggertower"(electromagneticplushadronic,indicatedasHitMaxingureA3)issummedwiththehighestofthefourbroadsideneighbortowers(indicatedasMaxEtingureA3).
Thesummedtransverseenergyofthetwotowersprovidesasharpereciencyturn-onwiththetrueEToftheparticles.
Thenon-isolatedcandidaterequirespassingoftwoshowerprolevetoes,therstofwhichisbasedonthene-grainECALcrystalenergyprole(FGveto).
ThesecondisCMSHighLevelTrigger9700.
20.
40.
60.
81051015202530354045501034141822263016202428ElectronPt(GeV)95%90%Efficiency0.
60.
70.
80.
91-2-1012EfficiencyηFigureA4.
TheeciencyoftheLevel-1triggerforsingleelectronsasafunctionoftheelectronpT.
Ontheright,theeciency,asfunctionofη,forelectronswithpT=35GeV/c.
basedontheHCALtoECALenergycomparison,e.
g.
Had/Emlessthan5%(HACveto).
TheisolatedcandidaterequirespassingtwoadditionalvetoestherstofwhichisbasedonpassingtheFGandHACVetoesonalleightnearestneighbors,andthesecondontheexistenceofatleastonequietcorner,i.
e.
,oneoftheve-towercornershasallcrystalsbelowaprogrammablethreshold,e.
g.
,1.
5GeV.
Eachcandidateischaracterizedbytheη,φindicesofthecalorimeterregionwherethehittowerislocated.
Ineachcalorimeterregion(4*4triggertowers)thehighestETnon-isolatedandisolatedelectron/photoncandidatesareseparatelyfound.
The16candidatesofbothstreamsfoundinawidertriggerregioncorrespondingto16calorimeterregions(coveringη*φ=3.
0*0.
7)arefurthersortedbytransverseenergy.
Thefourhighest-ETcandidatesofbothcategoriesaretransferredtotheGlobalCalorimeterTrigger(GCT)andretainedforprocessingbytheCMSglobaltrigger.
Thenominalelectron/photonalgorithmallowsbothnon-isolatedandisolatedstreams.
Thenon-isolatedstreamusesonlythehittowerinformationincludinganyleakageenergyfromthemaximumneighbortower.
Thisstreamwillbeusedatlowluminositytoprovidetheelectrontriggerfrombsemileptonicdecays.
Theisolationandshowershapetriggercutsareprogrammableandcanbeadjustedtotherunningconditions.
Forexample,athighluminositytheisolationcutscouldberelaxedtotakeintoaccounthigherpileupenergies.
Thespecicationoftheelectron/photontriggersalsoincludesthedenitionoftheηφregionwhereitisapplicable.
Inparticular,itispossibletodenedierenttriggerconditions(e.
g.
energythresholdsandisolationcuts)indierentrapidityregions.
Theeciencyoftheelectron/photonalgorithm,asafunctionoftheelectrontransversemomentum,fordierentthresholdsappliedatLevel-1,isshowninFigureA4.
Alsoshownistheeciency,asfunctionofpseudorapidityforelectronswithpT=35GeV/c.
ToconnecttheLevel-1thresholdtoaneectiverequirementontheelectrontransversemomentum,theelectronpTatwhichtheLevel-1triggeris95%ecient,isdeterminedasfunctionoftheLevel-1threshold.
ThisisshowninFigureA5.
Fromthisresult,therateforelectron/photontriggersasafunctionoftheeectivecutontheET,i.
e.
ofthepointCMSHighLevelTrigger980510152025303540455005101520253035404550Level-1threshold(GeV)T90=4.
12+0.
981*TL-1T95=5.
34+1.
010*TL-1ElectronPt(GeV)FigureA5.
TheelectronpTatwhichtheLevel-1Triggeris95%ecientasafunctionoftheLevel-1threshold.
110102103202530354045110102103202530354045Level-1ET(95%)(GeV)Rate(kHz)Level-1singlee.
m.
1034/cm2/sAllAfterFG+HoEAfterisolation10-1110220253035404510-1110102202530354045Level-1ET(95%)(GeV)Rate(kHz)Level-1singlee.
m.
2x1033/cm2/sAllAfterFG+HoEAfterisolationFigureA6.
Therateofthesingleelectron/photonLevel-1triggeratlow(left)andhigh(right)luminosity.
FGandHoErefertotheshowerproleandhadronicoverelectromagneticenergyisolationcriteria.
atwhichthetriggeris95%ecient,canbecomputed.
FigureA6showstheratesforsingleelectronsasafunctionoftheEToftheelectron(95%point).
Double–,triple–andquad–electron/photontriggerscanbedened.
Therequirementsontheobjectsofamulti-electron/photontrigger,namelytheenergythreshold,theclustershapeandisolationcutsandthe(η,φ)region,aresetindividually.
Requirementsonthe(η,φ)separationbetweenobjectscanalsobedened.
CMSHighLevelTrigger99TriggerTowerECALHCAL=0.
348PbWO4Crystal=1.
04FigureA7.
Jetandτtriggeralgorithms.
AppendixA.
3.
Jetandτ-jettriggersThejettriggerusesthetransverseenergysums(electromagneticplushadronic)computedincalorimeterregions(4*4triggertowersasshownifgureA7).
Intheforwardhadroncalorimetertheregionisthetriggertoweritself.
Thejettriggerusesa3*3calorimeterregionslidingwindowtechniquewhichspansthecomplete(η,φ)coverageoftheCMScalorimetersseamlessly.
ThecentralregionETisrequiredtobehigherthantheeightneighborregionETvalues.
Inaddition,thecentralregionETisrequiredtobegreaterthanaxedvalue,tosuppressnoise.
Thejetsandτ–jetsarecharacterizedbythetransverseenergyETin3*3calorimeterregions.
Thereforethesummationspans12*12triggertowersinthebarrelandtheendcapor3*3towersintheforwardhadroncalorimeter.
Theφsizeofthejetwindowisthesameeverywhere(60)whiletheηbinningisincreasingasafunctionofηaccordingtothecalorimeterandtriggertowersegmentation.
Thejetsarelabeledbytheir(η,φ)indices.
Singleandthree–prongdecaysofτ–leptonsformnarrowclustersofenergydepositsinthecalorimeter.
Sincethedecaysinvolvechargedpionswhichdepositenergiesinthehadroncalorimeter,theelectron/photontriggerdoesnotcapturethem.
Therefore,thetransverseprolesofactivetowerpatternsareanalyzedtotagnarrowjetsaspotentialτ–leptondecays.
AnactivetowerisdenedasatriggertowerwithECALorHCALETaboveaseparatelyprogrammablethreshold.
Theenergydepositineachtriggertower,ECALandHCALseparately,iscomparedtoaprogrammablethresholdtoobtaintwo4*4single-bitactivitypatterns.
Theenergydepositpatterninthe4*4regionisexaminedandifthepatterndoesnotmatchanyofthe1-,2-,3-and4-towerpatternsshowningureA7,thisregioncannotincludeaτ-cadidatetherefore,its"tau-veto"bitisset.
Atthenextstageofprocessing,overlapping3*3regions,i.
e.
,1212triggertowers,isconsidered.
These1.
044*1.
044ηφsumsdenejetsifthecentralregionhasmoreCMSHighLevelTrigger100energythanits8neighbors.
ThelogicalORofthetau-bitsofthese9regionsconstitutetheultimatetau-vetoforthejet.
Ifthisjetdoesnothavetau-vetoset,itisredenedasatau-jetandissortedinpTseparately.
Theτ-vetobitscanbeusedbothforτ-likeenergydepositidenticationandstringentisolation.
Countersofthenumberofjetsaboveprogrammablethresholdsinvariousηregionsareprovidedtogivethepossibilityoftriggeringoneventswithalargenumberoflowenergyjets.
Jetsintheforwardandbackwardhadroncalorimetersaresortedandcountedseparately(duetobackgroundη-dependence)buttheglobaltriggerusesthemseamlessly.
Thefourhighestenergycentralandforwardjets,andcentraltausinthecalorimeterareselected.
Theselectionofthefourhighestenergycentralandforwardjetsandthefourhighestenergytausprovidesenoughexibilityforthedenitionofcombinedtriggers.
Single,double,tripleandquadjet(includingτ-jet)triggersarepossible.
Thesinglejet(τ-jet)triggerisdenedbythetransverseenergythreshold,the(η,φ)regionandbyaprescalingfactor.
Prescalingwillbeusedforlowenergyjet(τ-jet)triggers,necessaryforeciencymeasurements.
Themulti-jet(τ-jet)triggersaredenedbythejetmultiplicityandthejettransverseenergythresholds,byaminimumseparationin(ηφ),andbyaprescalingfactor.
Theglobaltriggeracceptsthedenition,inparallel,ofdierentmulti-jet(τ-jet)triggerconditions.
AppendixA.
4.
TransverseEnergyTriggersTheETtriggersusethetransverseenergysums(Em+Had)computedincalorimeterregions(4*4triggertowersinbarrelandendcap).
ExandEyarecomputedfromETusingthecoordinatesofthecalorimeterregioncenter.
Thecomputationofmissingtransverseenergyfromtheenergyincalorimeterregionsdoesnotaectsignicantlytheresolutionfortriggerpurposes.
ThemissingETiscomputedfromthesumsofthecalorimeterregionsExandEy.
Thesumextendsuptotheendofforwardhadroniccalorimeter,i.
e.
,|η|=5.
ThemissingET(E/T)triggersaredenedbyathresholdvalueandbyaprescalingfactor.
Theglobaltriggeracceptsthedenition,inparallel,ofdierentmissingETtriggersconditions.
ThetotalETisgivenbythesumofthecalorimeterregionsET.
Thesumextendsuptotheendofforwardcalorimeter.
ThetotalETtriggersaredenedbyathresholdvalueandbyaprescalingfactor.
Theglobaltriggeracceptsthedenition,inparallel,ofdierenttotalETtriggersconditions.
Thetotalenergytriggerisimplementedwithanumberofthresholdswhichareusedbothfortriggerstudiesandforinputtotheluminositymonitor.
Someofthesethresholdsareusedincombinationwithothertriggers.
Otherthresholdsareusedwithaprescaleandonethresholdisusedforastand-alonetrigger.
ThelowerthresholdETtriggerprovidesagoodcalorimeterandtriggerperformancediagnostic.
ThetriggerisdenedasthescalarsumoftheETofjetsaboveaprogrammablethresholdwithatypicalvalueofjetET>10GeV.
ThistriggerisnotassusceptibleasthetotalETgivenbythesumofthecalorimeterregionsETdepositstobothnoiseandpileupeects.
AlthoughthetotalETisanecessarytechnicaltrigger,ithaslimitedusefromthephysicspointofview.
ThetriggercancapturehighjetmultiplicityeventssuchCMSHighLevelTrigger101asthosefromfullyhadronictopdecay,hadronicdecaysofsquarksandgluinos.
AlthoughtheseeventshaveseveralhundredGeV/c2energy,theymayactuallyfailthejettriggersbecausetheETofindividualjetscouldbesofterthanthethresholds.
Inaddition,thetriggercanuseindividuallycalibratedjetenergiesunlikethetotalETtriggerwhichcannotbeeasilycalibrated.
Foreachcalorimeterregionof4*4triggertowersa"Quiet"and"MIP"bitiscomputed.
TheQuietbitis"on"ifthetransverseenergyinthecalorimeterregionisbelowaprogrammablethreshold.
TheMIPbitinacalorimeterregionrequiresontopoftheQuietbitcondition,thatatleastoneofthe16triggertowershastheHCALFineGrainbit"on".
ThequietandMIPbitsareusedintheGlobalMuonTrigger.
AppendixA.
5.
TheLevel-1muontriggerThemuonmeasurementatCMSisperformedbyDriftTubes(DT)locatedoutsidethemagnetcoilinthebarrelregionandcathodeStripChambers(CSC)intheendcapregion.
TheCMSmuonsystemisalsoequippedwithResistivePlateChambers(RPC)bothinthebarrelandendcapregionsusedintriggeringandreconstruction.
TheDriftTubesystemiscomprisedoffourmuonstationsinterleavedwiththeironoftheyoketomakefulluseofthemagneticreturnux.
Eachstationincomprisedoftwoorthreesuperlayers(SL).
EachDTsuperlayerissplitinfourlayersofstaggereddrifttubes,whileeachCSCstationiscomprisedofsixlayersofcathodestripchambers.
TheDriftTubeandCathodeStripChambertriggerssystemsprocesstheinformationfromeachchamberlocallyandarerefereedtoaslocaltriggers.
Theyprovideonevector(positionandangle)permuonperstation.
TrackFinders(TF)collectthesevectorsfromthedierentstationsandcombinethemtoformmuontracks.
TheTrackFindersplaytheroleofaregionaltrigger.
Uptofourbest(highestpTandquality)muoncandidatesfromeachsystemareselectedandsenttotheGlobalMuonTrigger.
InthecaseofRPCthereisnolocalprocessingapartfromsynchronizationandclusterreduction.
HitsfromallstationsarecollectedbythePatternComparatorTrigger(PACT)whichdetectsthemuoncandidatesbasedontheoccurrenceofpredictedhitpatterns.
MuonSortersselectthetopfourmuonsfromthebarrelandthetopfourfromtheendcapsandsendthemtotheGlobalMuonTrigger(GMT).
TheGMTcomparestheinformationfromtheTF(DT/CSC)andthePACT(RPC)andattemptstocorrelatetheCSCandDTtrackswithRPCtracks.
Iftwocandidatesarematchedtheirparametersarecombinedtogiveoptimumprecision.
TheGMTcorrelatesthemuoncandidatetrackswiththecorrespondingcalorimetertowers,basedonthepositioninηφ,todetermineifthesemuonsareisolated.
QuietandMIPbitsdeliveredbytheCalorimeterTriggerareusedtoformanisolatedmuontriggerandtoconrmthemuontriggerusingthecalorimeterinformation.
TheCSCandDriftTubeTrackFindersexchangetracksegmentinformationintheregionwherethechambersoverlap.
CoarseRPCdatacanbesenttotheCSCtriggertohelpresolvespatialandtemporalambiguitiesinmultimuonevents.
Thenalensembleofmuonsaresortedbasedontheirinitialquality,correlationandpTandthefourtopcandidatesareCMSHighLevelTrigger102senttotheGlobalTrigger.
TransversemomentumthresholdsareappliedbytheGlobalTriggerforalltriggerconditions.
AppendixA.
5.
1.
DriftTube(DT)TriggerThedriftchambersdeliverdatafortrackreconstructionandfortriggeringondierentdatapathsatthelocaltriggerlevel.
Thetriggerfront-end(BunchandTrackIdentierorBTI),isusedinφandηtoperformaroughmuontrackt.
ItusesthefourlayersofDTsinonesuperlayertomeasurethepositionanddirectionoftriggercandidatetrackswithatleastthreehitsoutoffour.
Thealgorithmtsastraightlinewithinprogrammableangularacceptance.
TheBTIperformsthebunchcrossingassignmentofeveryfoundmuontrackcandidate.
Sincethismethodmustforeseealignmenttolerancesandneedstoacceptalignmentsofonlythreehits,thealgorithmcangeneratefalsetriggers.
HenceinthebendingplaneasystemcomposedofaTrackCorrelator(TRACO)andachamberTriggerServer(TS)isusedtoltertheinformationofthetwoφsuperlayersofachamber.
TheTRACO/TSblockselects,ateverycycleamongthetriggercandidates,atmosttwotracksegmentswiththesmallestangulardistances(i.
e.
higherpT)withrespecttotheradialdirectiontothevertex.
TracksegmentsfoundineachstationarethentransmittedtoaregionaltriggersystemcalledDriftTubeTrackFinder(DTTF).
ThetaskoftheTrackFinderistoconnecttracksegmentsdeliveredbythestationsintoafulltrackandassignatransversemomentumvaluetothenallyresolvedmuontrack.
Thesystemiscomprisedofsectors(72intotal),eachofthemcovering30intheφangle,andvewheelsinthez-direction.
EachSectorProcessorislogicallydividedinthreefunctionalunits-theExtrapolatorUnit(EU),theTrackAssembler(TA)andtheAssignmentUnits(AU).
TheExtrapolatorUnitattemptstomatchtracksegmentspairsofdistinctstations.
Usingthespatialcoordinateφandthebendingangleofthesourcesegment,anextrapolatedhitcoordinateiscalculated.
ThetwobestextrapolationspereachsourceareforwardedtotheTrackAssembler.
TheTrackAssemblerattemptstondatmosttwotracksinadetectorsectorwiththehighestrank,:i.
e.
exhibitingthehighestnumberofmatchingtracksegmentsandthehighestextrapolationquality.
OncethetracksegmentdataareavailabletotheAssignmentUnit,memory-basedlook–uptablesareusedtodeterminethetransversemomentumandtheφ.
Theηcoordinates,areassignedseparatelyusinghitsintheη-superlayersofthethreeinnermoststationandapplyingapatternmethod.
AppendixA.
5.
2.
CSCTriggerTheCSCLocalTriggerndsmuonsegments,alsoreferredtoasLocalChargedTracks(LCTs),inthe6-layerendcapmuonCSCchambers.
Muonsegmentsarerstfoundseparatelybyanodeandcathodeelectronicsandthentimecorrelated,providingprecisionmeasurementofthebendcoordinatepositionandangle,approximatemeasurementofthenon-bendanglecoordinate,andidenticationofthecorrectmuonbunchcrossingwithhighprobability.
TheprimarypurposeoftheCSCcathodetriggerelectronicsistomeasuretheφCMSHighLevelTrigger103coordinatepreciselytoallowagoodmuonmomentummeasurementuptohighmomentum.
Thechargecollectedonananodewireproducesanopposite-signsignalonseveralstrips,andprecisiontrackmeasurementisobtainedbychargedigitizationandpreciseinterpolationofthecathodestripcharges.
ThesixlayersarethenbroughtintocoincidenceinLCTpatterncircuitrytoestablishpositionofthemuontoanRMSaccuracyof0.
15stripwidths.
Stripwidthsrangefrom6-16mm.
TheprimarypurposeoftheCSCanodetriggerelectronicsistodeterminetheexactmuonbunchcrossingwithhigheciency.
Sincethedrifttimecanbelongerthan50ns,amulti-layercoincidencetechniqueintheanode"LocalChargedTrack"(LCT)patterncircuitryisusedtoidentifyamuonpatternandndthebunchcrossing.
ThetaskoftheCathodeStripChamberTrack-FinderistoreconstructtracksintheCSCendcapmuonsystemandtomeasurethetransversemomentum(pT),pseudo-rapidity(η),andazimuthalangle(φ)ofeachmuon.
ThemeasurementofpTbytheCSCtriggerusesspatialinformationfromuptothreestationstoachieveaprecisionsimilartothatoftheDTTrack-Finderdespitethereducedmagneticbendingintheendcap.
CathodeandanodesegmentsarebroughtintocoincidenceandsenttotheCSCSectorProcessorelectronicswhichlinksthesegmentsfromtheendcapmuonstations.
EachSectorProcessorunitndsmuontrackswithin60.
AsingleextrapolationunitformsthecoreoftheSectorProcessortriggerlogic.
Ittakesthethreedimensionalspatialinformationfromtwotracksegmentsindierentstations,andtestsifthosetwosegmentsarecompatiblewithamuonoriginatingfromthenominalcollisionvertexwithacurvatureconsistentwiththemagneticbendinginthatregion.
EachCSCSectorProcessorcannduptothreemuoncandidateswithin60.
ACSCmuonsortermoduleselectsthefourbestCSCmuoncandidatesandsendsthemtotheGlobalMuonTrigger.
AppendixA.
5.
3.
RPCTriggerTheRPCPatternTriggerLogic(PACT)isbasedonthespatialandtimecoincidenceofhitsinfourRPCmuonstations.
BecauseofenergylossuctuationsandmultiplescatteringtherearemanypossiblehitpatternsintheRPCmuonstationsforamuontrackofdenedtransversemomentumemittedinacertaindirection.
Therefore,thePACTshouldrecognizemanyspatialpatternsofhitsforagiventransversemomentummuon.
InordertotriggeronaparticularhitpatternleftbyamuonintheRPCs,thePACTperformstwofunctions:itrequirestimecoincidenceofhitsinpatternsrangingfrom3outof4muonstationsto4outof6muonstationsalongacertainroadandassignsapTvalue.
Thecoincidencegivesthebunchcrossingassignmentforacandidatetrack.
Thecandidatetrackisformedbyapatternofhitsthatmatcheswithoneofmanypossiblepre-denedpatternsformuonswithdenedtransversemomenta.
Thepre-denedpatternsofhitshavetobemutuallyexclusivei.
e.
apatternshouldhaveauniquetransversemomentumassignment.
Thepatternsaredividedintoclasseswithatransversemomentumvalueassignedtoeachofthem.
PACTisathresholdtrigger;itgivesamomentumcodeifanactualhitpatternisstraighterthananyofpre-denedpatternswithalowermomentumcode.
Thepatternswilldependonthedirectionofamuoni.
e.
onitsφandη.
CMSHighLevelTrigger104AppendixA.
5.
4.
GlobalMuonTrigger(GMT)TheGMTreceivesthebestfourbarrelDTandthebestfourendcapCSCmuonsandcombinesthemwith4+4muonssentbytheRPCPACT.
Itperformsamatchingbasedontheproximityofthecandidatesin(ηφ)space.
Iftwomuonsarematched,theirparametersarecombinedtogiveoptimumprecision.
TheGMTalsocontainslogictocancel"ghost"tracksthatarisewhenasinglemuonisfoundbymorethanonemuonsystemandisnototherwisematched,suchasattheboundarybetweentheDTandCSCmuonsystems.
Theselectedmuoncandidatesarerankedbasedontheirtransversemomentum,qualityandtosomeextentpseudorapidityandthebestfourmuoncandidatesintheentireCMSdetectoraresenttotheGlobalTrigger.
TheGlobalMuonTriggeralsoreceivesinformationfromthecalorimeters.
TheRegionalCalorimeterTriggersendstwobitsbasedonenergymeasurementsrepresentingisolationandcompatibilitywithaminimumionizingparticleinη*φ=0.
35*0.
35triggerregions.
TheGMTextrapolatesthemuontracksbacktothecalorimetertriggertowersandthevertexandappendsthecorrespondingisolationandminimumionizingbits(ISOandMIP)tothetrackdataindicatingisolationorconrmationofthemuonbythecalorimeter.
ThemuontrackdatasenttotheGTarethe,thesignofthecharge,theηandφaswellastheISOandMIPbits.
AppendixA.
6.
TheLevel-1GlobalTriggerTheGlobalTriggeracceptsmuonandcalorimetertriggerinformation,synchronizesmatchingsub-systemdataarrivingatdierenttimesandcomputesupto128triggeralgorithmsinparallel.
ThetriggerdecisioniscommunicatedtotheTriggerandControlSystem(TCS)fordistributiontothesub-systemstoinitiatethereadout.
TheglobaltriggerdecisionismadeusinglogicalcombinationsofthetriggerdatafromtheGlobalCalorimeterandGlobalMuonTriggers.
TheLevel-1Triggersystemsortsrankedtriggerobjects,ratherthanhistogrammingobjectsoveraxedthreshold.
ThisallowsalltriggercriteriatobeappliedandvariedattheGlobalTriggerlevelratherthanearlierinthetriggerprocessing.
Alltriggerobjectsareaccompaniedbytheircoordinatesinηφspace.
Formuoncandidatesthechargeisalsodelivered.
ThisallowstheGlobalTriggertovarythresholdsbasedonthelocationofthetriggerobjects.
ItalsoallowstheGlobalTriggertorequiretriggerobjectstobecloseoroppositefromeachother.
Inaddition,thepresenceofthetriggerobjectcoordinatedatainthetriggerdata(whichisreadoutrstbytheDAQafteraLevel-1acceptdecision)permitsaquickdeterminationoftheregionsofinterestwherethemoredetailedHLTanalysisshouldfocus.
Besideshandlingphysicstriggers,theGlobalTriggerprovidesfortestandcalibrationruns,notnecessarilyinphasewiththemachine,andforprescaledtriggers,asthisisanessentialrequirementforcomputingtriggereciencies.
TheGlobalLevel-1TriggerisresponsiblefordecidingwhethertoacceptorrejectaneventandforgeneratingthecorrespondingL1Acceptsignal(L1A).
ThenalL1AdecisionisthelogicalORofallalgorithmsusedatL1.
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TheTCSautomaticallyprescalesorshutsotheL1Acasethedetectorreadoutbuersareatriskofoverow.
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