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Compact Muon Solenoid Experiment Discovery Potential for Supersymmetry in Same-Charge Di-lepton Events

Permanent Link: http://ufdc.ufl.edu/UFE0041613/00001

Material Information

Title: Compact Muon Solenoid Experiment Discovery Potential for Supersymmetry in Same-Charge Di-lepton Events
Physical Description: 1 online resource (147 p.)
Language: english
Creator: Pakhotin, Yuriy
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2010

Subjects

Subjects / Keywords: collider, compact, hadron, large, leptons, model, muon, particles, solenoid, standard, supersymmetry
Physics -- Dissertations, Academic -- UF
Genre: Physics thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Compact Muon Solenoid Experiment Discovery Potential for Supersymmetry in Same-charge Di-lepton Events Same-charge di-lepton events provide a very clean experimental signature for Supersymmetry (SUSY) search. This work studies the Compact Muon Solenoid (CMS) experiment search potential for new physics with same-charge, isolated di-leptons accompanied by jets and large missing transverse energy. The results show that CMS sensitivity for new physics at 7 TeV with integrated luminosity 100 pb^-1 will exceed current Tevatron limits. Muon detection for SUSY discovery in the forward direction is accomplished using cathode strip chambers (CSC). These detectors identify muons, provide a fast muon trigger, and give a precise measurement of the muon trajectory. There are 468 six-plane CSCs in the system. The efficiency of finding muon trigger primitives (muon track segments) was studied using 36 CMS CSCs and cosmic ray muons during the Magnet Test and Cosmic Challenge (MTCC) exercise conducted by the CMS experiment in 2006. The efficiency of finding 2-dimensional trigger primitives within 6-layer chambers was found to be 99.93+-0.03%.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Yuriy Pakhotin.
Thesis: Thesis (Ph.D.)--University of Florida, 2010.
Local: Adviser: Mitselmakher, Gena.
Local: Co-adviser: Korytov, Andrey.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2012-08-31

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2010
System ID: UFE0041613:00001

Permanent Link: http://ufdc.ufl.edu/UFE0041613/00001

Material Information

Title: Compact Muon Solenoid Experiment Discovery Potential for Supersymmetry in Same-Charge Di-lepton Events
Physical Description: 1 online resource (147 p.)
Language: english
Creator: Pakhotin, Yuriy
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2010

Subjects

Subjects / Keywords: collider, compact, hadron, large, leptons, model, muon, particles, solenoid, standard, supersymmetry
Physics -- Dissertations, Academic -- UF
Genre: Physics thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Compact Muon Solenoid Experiment Discovery Potential for Supersymmetry in Same-charge Di-lepton Events Same-charge di-lepton events provide a very clean experimental signature for Supersymmetry (SUSY) search. This work studies the Compact Muon Solenoid (CMS) experiment search potential for new physics with same-charge, isolated di-leptons accompanied by jets and large missing transverse energy. The results show that CMS sensitivity for new physics at 7 TeV with integrated luminosity 100 pb^-1 will exceed current Tevatron limits. Muon detection for SUSY discovery in the forward direction is accomplished using cathode strip chambers (CSC). These detectors identify muons, provide a fast muon trigger, and give a precise measurement of the muon trajectory. There are 468 six-plane CSCs in the system. The efficiency of finding muon trigger primitives (muon track segments) was studied using 36 CMS CSCs and cosmic ray muons during the Magnet Test and Cosmic Challenge (MTCC) exercise conducted by the CMS experiment in 2006. The efficiency of finding 2-dimensional trigger primitives within 6-layer chambers was found to be 99.93+-0.03%.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Yuriy Pakhotin.
Thesis: Thesis (Ph.D.)--University of Florida, 2010.
Local: Adviser: Mitselmakher, Gena.
Local: Co-adviser: Korytov, Andrey.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2012-08-31

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2010
System ID: UFE0041613:00001


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Iwouldliketothankmyadviser,Prof.GuenakhMitselmakher,forhissupport,encouragement,instructionsandpatientpointingmetothegoal.Ibelievehisadvisesshapedmypersonalityandimprovedmyselfinmanydifferentways.IwanttothankProf.AndreyKorytov.Thisthesiswouldneverhasbeennished(orevenhasbeenstarted)withouthishelp,supportandinvaluablecontribution.IamgratefultoProf.KonstantinMatchevfortheoreticalguidanceofthisworkandalltimehespentexplainingmetheessenceofSupersymmetry.IwouldliketothankProf.DarinAcostaforallhishelp,andadvises.IthankProf.VladimirRakovwhokindlyagreedtobecomeanexternalmemberofmycommitteeandreviewthiswork.ThankstoallpeoplewhosehelpIhavereceived.IthankRichardCavanaugh(nowattheUniversityofIllinoisatChicago)forhishelp,supportandcontributionintotheanalysisfromtheverybeginning,forhispatiencewhileintroducingmetothebasicsofCMSsoftwareanddatamanagement.IthankBobbyScurlockwithwhomIstartedthisanalysis.Hisphysicsandsoftwareadviseswerereallyhelpful.ThisthesiswouldbeunnishedwithouthardworkandimportantcontributionsmadebyDidarDoburandRonnyRemington.Iamreallythankfultothem.IwouldliketothankAlexeyDrozdetskiy,KhristianKotovandVictorBarashkofornumerousanswersonmyquestionsandimportantadvisestheygaveme.IwanttothankJohnYelton,PaulAvery,IvanFuric,DayongWang,MingshuiChen,TreySellers,LanaMuniz,SeanGoldberg,JoeGartner,GianPieroDiGiovanni,JonatanPiedra,NickKypreos,MichaelSchmitt,ValdasRapseviciusforallhelpIreceivedfromthem.IwouldliketothankallUFTier2andHPCpeopleBockjooKim,DimitriBourilkov,YujunWu,YuFu,CharlieTaylor,CraigPresscottandJorgeRodriguez(nowattheFloridaInternationalUniversity)forkeepingverycomplexcomputersystemrunningandprovidingsmoothaccesstoit. 4

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page ACKNOWLEDGMENTS .................................. 4 LISTOFTABLES ...................................... 10 LISTOFFIGURES ..................................... 12 ABSTRACT ......................................... 17 CHAPTER 1PREFACE ....................................... 18 2STATUSOFTHEFIELD ............................... 20 2.1Introduction ................................... 20 2.2ElementaryParticles .............................. 20 2.2.1Leptons ................................. 20 2.2.2Quarks .................................. 21 2.2.3Antiparticles ............................... 22 2.3FundamentalForces .............................. 23 2.3.1Stronginteraction ............................ 24 2.3.2Electromagneticinteraction ...................... 24 2.3.3Weakinteraction ............................ 25 2.3.4Gravitationalinteraction ........................ 26 2.4StandardModel ................................. 28 2.4.1QuantumChromodynamics ...................... 28 2.4.2UniedElectroweakModel ....................... 29 2.4.3StandardModelLagrangian ...................... 29 2.5Supersymmetry ................................. 30 2.5.1MinimalSupersymmetricStandardModelExtension ........ 31 2.5.2MinimalSupergravity .......................... 32 2.5.3R-Parity ................................. 33 2.5.4SearchforSUSYwithSame-chargeDi-leptonEvents ........ 33 2.5.5CurrentExperimentalLimitsforMinimalSupergravity ........ 34 2.5.5.1DirectSearchatLEP2 .................... 34 2.5.5.2DirectSearchatTevatron .................. 35 3STATUSOFTHEEXPERIMENT .......................... 38 3.1Introduction ................................... 38 3.2TheLargeHadronCollider .......................... 38 3.2.1PhysicsRequirements ......................... 38 3.2.2MachineLayout ............................. 40 3.2.3MagneticandCryogenicSystems ................... 43 3.2.4VacuumSystem ............................ 44 7

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............................. 45 3.2.6TheRFSystems ............................ 47 3.2.7BeamDumping ............................. 47 3.2.8PowerandEnergyConsumption ................... 49 3.3TheCompactMuonSolenoidDetector .................... 49 3.3.1GeneralDescription .......................... 49 3.3.2CoordinateSystem ........................... 51 3.3.3SuperconductingMagnetSystemandIronYoke ........... 52 3.3.4InnerTrackingSystem ......................... 53 3.3.5ElectromagneticCalorimeterSystem ................. 55 3.3.6HadronCalorimeterSystem ...................... 57 3.3.7MuonSystem .............................. 59 3.3.7.1CathodeStripChambersinEndcaps ........... 59 3.3.7.2DriftTubesinBarrel ..................... 61 3.3.7.3ResistivePlateChambers .................. 63 3.3.8Trigger,DataAcquisitionandOfineComputingSystems ..... 64 3.4FirstResultsoftheExperiment ........................ 66 3.4.1TheCMSResultswithCosmicMuons ................ 66 3.4.2TheLHCTimeline ........................... 67 3.4.3TheCMSResultswithppCollisionsatp ................................. 68 3.4.4TheCMSResultswithppCollisionsatp ......... 69 4CMSDISCOVERYPOTENTIALFORSUSYINSAME-CHARGEDI-LEPTONEVENTSINppCOLLISIONSWITHp ...... 73 4.1Introduction ................................... 73 4.2MonteCarlogenerationanddetectorsimulationofdatasamples ..... 74 4.2.1AnalysisFlow .............................. 74 4.2.2SupersymmetrySignals ........................ 75 4.2.3StandardModelBackgrounds ..................... 78 4.2.3.1ProductionofQCD ...................... 78 4.2.3.2ProductionofTopQuarkPairs ............... 79 4.2.3.3ProductionofElectro-WeakSingleBosons ........ 80 4.2.3.4ProductionofElectro-WeakDoubleBosons ........ 80 4.3EventReconstruction ............................. 81 4.3.1Trigger .................................. 81 4.3.2PhysicsObjectsReconstructionandIdentication .......... 81 4.3.2.1MuonsReconstructionandIdentication ......... 82 4.3.2.2ElectronsReconstructionandIdentication ........ 82 4.3.2.3JetsReconstruction ..................... 83 4.3.2.4MissingTransverseEnergy ................. 84 4.4DiscriminatingObservables .......................... 84 4.4.1TwoSame-chargeIsolatedLeptons .................. 84 4.4.2HighETJetsandTheirMultiplicity .................. 86 8

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...................... 87 4.4.4OptimizationProcedure ........................ 87 4.4.5Stabilityofsensitivity .......................... 89 4.5DataDrivenMethodsandSystematicuncertainties ............. 90 4.5.1Same-chargeDi-muonChannel .................... 90 4.5.1.1DataDrivenMethodtoEstimatetheQCDBackground .. 90 4.5.1.2DataDrivenMethodtoEstimateTop(tt)andSingleBoson(W=Z+jets)Backgrounds .................. 91 4.5.2Same-chargeDi-electronandElectron-MuonChannels ...... 92 4.5.3Systematicuncertainties ........................ 92 4.6Resultsforp ............................ 93 4.7Resultsforp ............................. 93 4.8Conclusion ................................... 95 5EFFICIENCYOFFINDINGMUONTRACKTRIGGERPRIMITIVESINCMSCATHODESTRIPCHAMBERS ........................... 98 5.1Introduction ................................... 98 5.2LocalChargedTracks ............................. 98 5.3MagnetTestandCosmicChallengeSetup .................. 100 5.4OfineEventSelection ............................. 102 5.5EfciencyMeasurement ............................ 103 5.6Conclusions ................................... 107 APPENDIX AESTIMATORUSEDFORSIGNIFICANCECALCULATION ............ 108 BESTIMATORUSEDFOREXCLUSIONLIMITSCALCULATION ......... 110 CTHELM0MSUGRABENCHMARKSAMPLE ................... 111 DVALIDATIONOFFASTSIMULATIONOFMSUGRASAMPLES ......... 123 ETRACKSEGMENTSRECONSTRUCTEDOFFLINE ............... 127 REFERENCES ....................................... 134 BIOGRAPHICALSKETCH ................................ 147 9

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Table page 2-1Propertiesofleptons[ 12 ]. .............................. 21 2-2Propertiesofquarks[ 12 ]. .............................. 21 2-3Propertiesoffundamentalforces[ 12 ]. ....................... 23 2-4ParticlesandtheirsuperpartnerswithintheMSSMframework. ......... 32 2-5Masslowerlimitsforsleptonsat95%C.L. ..................... 34 4-1InputparametersoffullysimulatedandreconstructedCMSmSUGRAbenchmarkpoints. ......................................... 76 4-2NumberofgeneratedMCeventsoffullysimulatedandreconstructedCMSmSUGRAbenchmarkpoints. ............................ 77 4-3CrosssectionsofCMSmSUGRAbenchmarkpoints. ............... 78 4-4CrosssectionsofQCD(bb)backgroundsamplesindifferentHTranges. .... 79 4-5NumberofgeneratedMCeventsoffullysimulatedandreconstructedQCD(bb)backgroundsamplesindifferentHTranges. ................. 79 4-6CrosssectionsofSM(noQCD)backgroundsamples. .............. 80 4-7NumberofgeneratedMCeventsoffullysimulatedandreconstructedSM(noQCD)backgroundsamples. ............................. 80 4-8Muonpreselectioncuts. ............................... 83 4-9Electronpreselectioncuts. ............................. 83 4-10Jetpreselectioncuts. ................................ 83 4-11Optimizedselectioncutsforallsame-chargedi-leptonchannels. ........ 89 4-12Numberofevents(atLHCenergyp 90 4-13SummaryofsystematicuncertaintiesforSUSYsignalincludedintheanalysis. 93 4-14Numberofevents(atLHCenergyp ...... 95 5-1Efcienciestodetectmuon2d-LCTsbyME+2chamberswithoutducialcuts.Theerrorsarestatistical. .............................. 107 10

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......................................... 107 D-1Numberofevents(normalizedtoanintegratedluminosityof100pb1)forSUSYLM0FullSimandFastSimsamplesaftersequentiallyapplyingthenalsetofcutsforallsame-chargedi-leptonchannels. .................... 123 E-1Numberofevents(withfractioninbrackets)fordifferentnumbersofanode(AS)andcathode(CS)segmentsintheME+2chambers. ............ 133 11

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Figure page 2-1Schemeoftree-levelinteractionsinStandardModel. ............... 30 2-2Exclusionlimits(at95%C.L.)onsparticlemassesfromthenon-observationofanysignalexcessoverbackgroundinLEP2experiments.Left:Masslowerlimitforsleptons(mlR).Right:Masslowerlimitforcharginos(01). ........ 35 2-3Theredregionsshowtheareas(left:insquarkandgluinomassesplane;right:inm0-m1=2plane)excluded(at95%C.L.)byD?experimentatTevatronwith2.1fb1ofdatafromthenon-observationofanysignalexcessoverbackgroundintheframeworkofmSUGRAassumingR-parityconservation[ 120 ].Exclusionsbyotherexperimentsarealsoshownforcomparison. .............. 36 2-4Theredregionsshowtheareas(left:insquarkandgluinomassesplane;right:inm0-m1=2plane)excluded(at95%C.L.)byCDFexperimentatTevatronwith2.0fb1ofdatafromthenon-observationofanysignalexcessoverbackgroundintheframeworkofmSUGRAassumingR-parityconservation[ 121 ].Exclusionsbyotherexperimentsarealsoshownforcomparison. .............. 36 2-5Theblueregionsonleftplotshowtheareas(inm0-m1=2plane)excluded(at95%C.L.)byCDFexperimentwith3.2fb1ofdatafromthenon-observationofanytri-leptonsignalexcessoverbackgroundintheframeworkofmSUGRAassumingR-parityconservation[ 123 ].Thegreenregionsonrightplotshowtheareas(inm0-m1=2plane)excluded(at95%C.L.)byD?experimentwith2.3fb1ofdatafromthenon-observationofanytri-leptonsignalexcessoverbackgroundintheframeworkofmSUGRAwithR-parityconservation[ 124 ]. .. 37 3-1TheLHCgeographicallocationonmap(left)andtunnelscheme(right). .... 40 3-2Transversecross-sectionsoftheLHCtunnel(left)andcryodipole(right). .... 43 3-3SchematicrepresentationoftheLHCinjectorchain(dimensionsnotproportionaltomachinesrealsize). ................................ 46 3-4AperspectiveviewoftheCMSdetector. ...................... 50 3-5PropagationofdifferentparticlesthroughtheCMSdetector. ........... 51 3-6OverallCMScoordinatesystem. .......................... 52 3-7Left:perspectivedrawingoftheCMStracker.Right:schematiccrosssectionthroughtheCMStracker.Eachlinerepresentsadetectormodule. ....... 54 3-8Left:perspectivedrawingoftheCMSelectromagneticcalorimetershowingthearrangementofcrystalmodules,supermodulesandendcaps,withthepreshowerinfront.Right:transversesectionthroughtheCMSelectromagneticcalorimeter,showinggeometricalconguration. .................. 56 12

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............ 58 3-10Left:Aschematicquarter-viewoftheCMSdetector(CSCsoftheEndcapMuonsystemarehighlighted;MEstandsforMuonEndcapchambers).Right:AphotooftheME+2diskanditsstationsofcathodestripchambers. ........... 60 3-11Left:SchematicviewofaCMScathodestripchamber.Thecutoutinthetoppanelallowsonetoseetheradialfan-shapedcathodestripsandanodewiresrunningacrossthestrips(onlyafewwiresareshown).Right:AnillustrationoftheCSCoperationprinciple.Anelectronavalancheresultingfromamuontraversingagasgapproducesasignalontheanodewireswhichinducesadistributedchargeoncathodestrips. ........................ 62 3-12Left:ApatternofwiregrouphitscreatedbyamuonpassingthroughaCSC.Right:Apatternofinducedchargesonstripsandcomparatorhalf-striphitscreatedbyapassingmuon. ............................. 62 3-13SchematiclayoutoftheCMSmuondrifttubeschambersononeofthe5barrelwheels. ........................................ 63 3-14Left:SchematiclayoutofRPCstationRBononeofthe5barrelwheels.Center:schematic(r;)layoutofRPCstationRE2onthebacksideoftherstendcapyoke.Right:photoofRPCstationRE2onthebacksideoftheYE-1yoke.Theinnerringhasbeenstagedandisabsenthere. ............... 64 3-15ArchitectureoftheCMSDAQsystem. ....................... 65 3-16Left:standalonecosmicmuoncrossingtheCMSdetectorfromtoptobottom,recordedinCRAFT08,leavingsignalsinthemuonsystem,andcalorimeters.Right:globalcosmicmuoncrossingtheCMSdetectorfromtoptobottom,recordedinCRAFT08,leavingsignalsinthemuonsystem,trackingdetectorsandcalorimeters[ 140 ]. ............................... 67 3-17TheluminosityintegratedbythefourLHCexperiments. ............. 68 3-18Left:InvariantmassdistributionoftheJ=!events.Right:InvariantmassdistributionoftheJ=!eeevents. ..................... 71 3-19Left:EventdisplayoftheW!candidate.Right:TransversemassdistributionoftheW!events. ................................ 71 3-20Left:EventdisplayoftheW!ecandidate.Right:TransversemassdistributionoftheW!eevents. ................................ 71 3-21Left:EventdisplayoftheZ!candidate.Right:InvariantmassdistributionoftheZ!events. ................................ 72 13

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................................ 72 4-1Anexampleofdiagramshowingasquark-gluinoproductioneventfollowingcascadedecays,resultingintwosame-chargemuons. .............. 74 4-2TheLM0mSUGRAsampleusedforoptimizationisshownasstar(?)inthem0-m1=2parametersplane.OtherofcialCMSmSUGRAbenchmarkpointsareshownassolidcircles().OthermSUGRAparameters(tan,sign,andA0)arexedforeachpointasshowninTable 4-1 .ExcludedregionsformSUGRAwithtan=3,>0,andA0=0byparticleexperiments(LEPmassesofcharginoandsleptonsshadedarea,CDFdirectsearchforsuperpartnerswithtrileptonsignaturesolidbluearea)arealsoshown.Referencelinesofequalmassesfordifferentsuperparticlesareplotted. ............... 75 4-3Next-to-leadingordercrosssections(left)andk-factors(right)forLHCcenterofmassenergyp ....... 78 4-4Transversemomentumofreconstructedleading(topleft)andnext-to-leading(topright)muonsinsame-chargedi-muonchannelandtransversemomentumofreconstructedleading(bottomleft)andnext-to-leading(bottomright)electronsinsame-chargedi-electronchannelforSUSYLM0(emptyredhistogram)andtt(shadedbluehistogram)samples. ........................ 85 4-5Relativeisolationofreconstructedmostisolated(lefttop)andleastisolated(righttop)muonsinsame-chargedi-muonchannelandrelativeisolationofreconstructedmostisolated(lefttop)andleastisolated(righttop)electronsinsame-chargedi-electronchannelforSUSYLM0(emptyredhistogram)andtt(shadedbluehistogram)samples. ......................... 87 4-6Numberofjets(topleft)andETofleading(topright),next-to-leading(bottomleft)andnext-to-next-to-leading(bottomright)jetsforSUSYLM0(emptyredhistogram)andtt(shadedbluehistogram)samples. ............... 88 4-7MissingtransverseenergyforSUSYLM0(emptyredhistogram)andtt(shadedbluehistogram)samples. .............................. 88 4-8Signicancevs.cutonETof3rdjet. ........................ 89 4-9TheisolationtemplateformuonsfromQCD(blueline).Theisolationdistributionformuonsfromttisshownforcomparison(redline). ............... 92 14

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........................ 94 4-11Top:theCMS5reachcontoursatp ........................ 96 5-1WiregroupsbitpatternusedforconstructingALCTs.Thekeywiregroupismarkedwithacross. ................................. 100 5-2ComparatorbitpatternsusedforconstructingCLCTs.Thekeyhalf/di-stripismarkedwithacross.Thestraight-throughpattern(left)correspondstohighpTmuons,whilemoreinclinedpatternswoulddetectsoftermuons. ....... 100 5-3CSCsthattookdataduringtheMTCC.HighlightedchamberswereoperationalduringtheMTCC.Left:Sideview.ThesolidboxesschematicallyshowthelocationsofALCTsthatwereactuallyfoundforamuonin3chambers.TheopenboxindicatesthepredictedALCTpositionintheME+2stationforthismuonbasedonthemeasurementsinME+1andME+3.Right:TransverseviewoftheME+2station. .............................. 101 5-4ScreenshotoftheinteractiveIGUANA-basedeventdisplay,showingCSCswithstripandwirehitsfromacosmicmuonthatpassedthrough3stationsoftheEMUsystem. ................................... 104 5-5PredictedpositionsofmuonhitsinME+2=1(left)andME+2=2(right)chambers. 104 5-6PredictedpositionsofmuonhitsinME+2=1(left)andME+2=2(right)chamberswhenLCTsinME+2arelost. ............................ 105 5-7EfciencytoreportamuonLCTasafunctionoftrackanglewithoutducialcuts(left)andafterexcludingsemi-deadzones(right)inME+2chambers.Thepredictedefciencycurvebasedongeometricanalysisisshownasthesolidline. ....................................... 105 5-8MuonhitsresidualsinME+2=1(left)andME+2=2(right)chambers. ...... 106 15

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177 ]. ............. 111 D-1Transversemomentumofreconstructedleading(topleft)andnext-to-leading(topright)muonsinsame-chargedi-muonchannelandtransversemomentumofreconstructedleading(bottomleft)andnext-to-leading(bottomright)electronsinsame-chargedi-electronchannelforSUSYLM0FullSim(emptyredhistogram)andSUSYLM0FastSim(shadedgreenhistogram)samples. .......... 124 D-2Relativeisolationofreconstructedmostisolated(lefttop)andleastisolated(righttop)muonsinsame-chargedi-muonchannelandrelativeisolationofreconstructedmostisolated(lefttop)andleastisolated(righttop)electronsinsame-chargedi-electronchannelforSUSYLM0(emptyredhistogram)andtt(shadedgreenhistogram)samples. ........................ 125 D-3Numberofjets(topleft)andETofleading(topright),next-to-leading(bottomleft)andnext-to-next-to-leading(bottomright)jetsforSUSYLM0(emptyredhistogram)andtt(shadedgreenhistogram)samples. .............. 125 D-4MissingtransverseenergyforSUSYLM0(emptyredhistogram)andtt(shadedgreenhistogram)samples. ............................. 126 E-1Comparatorbitpatternsusedforconstructingcathodesegments.Thekeyhalf-stripismarkedwithacross. .......................... 128 E-2MuonhitresidualsinME+2=1chambersafteranalgorithmsearchfortracksegmentsandapplyingtheCOGtechniquetondthemuontracksegmentcoordinates. ...................................... 129 E-3MuonhitresidualsinME+2=2chambersafteranalgorithmsearchfortracksegmentsandapplyingtheCOGtechniquetondthemuontracksegmentcoordinates. ...................................... 130 E-4Cosmicraymuonspectrum(left).Muonhitdx-residualsinME+2=2chambers(right),wherethehistogramcorrespondstothemeasureddataandthelinegivesourexpectationsforthemultiplescatteringcontribution. .......... 131 E-5Distributionsofnumbersofanode(left),cathode(center),andcombined2-dtracksegmentsfoundintheME+2chambers. ................... 131 E-6Quality(numberoflayerswithhits)distributionsofprimary(upperplots)andsecondary(lowerplots)segmentsinME+2chambers.Theprimarysegmentistheoneclosesttothepredictedmuontrackposition;allothersaresecondary. 132 16

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2 introducesthemotivationforsearchforphysicsphenomenabeyondStandardModel(SM).OneofthefavoritecandidatesfornewphysicsisSupersimmetry(SUSY).ItisoutlinedinthisChapter.ThesimplestSUSYmodel,MinimalSupergarvity(mSUGRA),isalsodescribedintheChapter 2 .Finally,thecurrentboundsfromdifferentexperimentalsearchesforSUSYarereviewed.Chapter 3 focusesonadescriptionoftheLargeHadronCollider(LHC)andtheCMSdetector.Majorsystemsofthefacilitiesarereviewed.AttheendoftheChapterresultsobtainedduringcosmicandrstcolliderrunsareoutlined.Chapter 4 isthecoreofthedissertation.Itfocusesonanexplanationofanalysispathandoptimizationprocedureusingsimulatedeventswithsame-charge,isolateddi-leptonsaccompaniedbyjetsandlargemissingtransverseenergy.Projected95%CLexclusionlimitsand5discoverycontoursformSUGRAarereportedfor100pb1ofintegratedluminosityattheLHCenergiesp 18

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5 describesthismeasurement.Theobtainedefciencyhadexceededthedesignspecicationandwasusedasabenchmarkinlaterstudies.Theworkdescribedinthisdissertationisdonebytheauthor,asamemberoftheCMScollaboration. 19

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1 4 ].Thecurrentstatusoftheeldisbrieyreviewedinthissection. 2.2.1LeptonsTheelectron[ 5 ]wastherstdiscoveredelementaryparticle.Itisnegativelyelectricallychargedwithmagnitudee=1.61019Cwhichiscommonlyusedasaunitofelectriccharge1.Therearetwootherobservedchargedparticles,muon[ 6 ]andtau[ 7 ]thathaveallthesamepropertiesaselectronexceptthemassandmeanlifetime.Theseparticleswerecalledleptons.Therearethreeotherobservedneutralavorsofleptonsneutrinos[ 8 ].Commonnotationforchargedleptonsisl,andforneutral.Thesixcurrentlydiscoveredleptonsjoinintopairsformingthreegenerations.PropertiesofleptonsaresummarizedinTable 2-1 .Massesandmeanlifetimesofelectrons,muonsandtausarewellmeasured.Neutrinooscillationsgivecompellingevidencethatneutrinosaremassive[ 9 10 ]. 20

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Propertiesofleptons[ 12 ]. Generation Flavor Charge Mass Meanlifetime name notation (e) (MeV=c2) (s) 1 electron 0.51 2 muon 106 2.2106 large 3 tau 1777 2.91013 large Directelectronneutrinomassmeasurementisunderway[ 11 ].Measuredlowerlevelsonmeanlifetimesforneutrinosarelargeanddependonmassrangesandmixingparameters[ 12 ].TheyarenotreportedinTable 2-1 13 ]andneutrons[ 14 ],theirstructuralparts(partons)werepredicted[ 15 19 ]andthenobserved[ 20 26 ].Theseparticleswerecalledquarks.Commonnotationforquarksisq.Sixcurrentlydiscoveredquarksjoinintopairsformingthreegenerations.PropertiesofquarksaresummarizedinTable 2-2 Table2-2. Propertiesofquarks[ 12 ]. Generation Flavor Charge Mass(inthe name notation (e) (MeV=c2) 1 up 1.5to3.0 down 3to7 2 charm 1.250.09103 9525 3 top 172.3+10.27.6103 4.200.07103 2.3.1 formoredetails)quarksareneverfoundinisolationandwereobservedonlyindirectlywithinotherparticles.Particlesmadeofquarksarecalledhadrons.Allquarkscarryfractionalelectricalcharge,however,hadronsalways 21

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27 28 ],tetraquarks[ 29 ],hybrids[ 30 ],etc)andexoticbaryons(pentaquarks[ 31 32 ],Hdi-baryon[ 33 ],supersymmetricR-baryon[ 34 ],etc)arepredictedinsometheoriesbutwerenotconvincinglyobservedyet[ 12 ].Quarkmassesaremeasuredindirectlythroughtheirinuenceonthepropertiesofhadronsandaredependentontheparticulartheoreticalframeworkthatisusedtodenethem.Allleptonsandquarksarefermionsbecausetheyhavespin1=2andobeyFermi-Diracstatistics.Hence,onlyonefermioncanoccupyaquantumstateatagiventime.Noexperimentalevidencesforleptonsandquarksconstituents,preons[ 35 ],havebeenfound.Therefore,leptonsandquarksarecurrentlyconsideredaselementarypoint-likeparticles.Afourthgenerationofleptonsandquarkshasbeensearchedforbutnoevidencehasbeenobserved[ 12 ].Ithasbeenindirectlyshown[ 36 ]thatnomorethanthreegenerations(withlightneutrino)exist.Onlytherstgenerationofleptonsandquarksgenerallyarecommoninthemodernuniverse.Highergenerationparticlesareunstableanddecayquickly.Tocreatetheseparticlesandtostudytheirpropertieshighenergycollisionsatparticleacceleratorsareused. 37 ]basedonchargeconjugation(C)symmetryandthenweresuccessfullyobservedinexperiment[ 38 ].Antimatterisnotcommoninthemodernuniverse.Baryogenesisistheprocessthoughttoberesponsibleforthematter-antimatterasymmetry[ 39 ].Themodelofbaryogenesisincludesthe 22

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2-3 andreviewedinfollowingfoursubsections. Table2-3. Propertiesoffundamentalforces[ 12 ]. Force Carrierparticle name range strength name notation charge mass (m) at1GeV (e) (MeV=c2) strong 1015 gluon 0 electromagnetic photon 1018 80.4103 91.2103 40 41 ].Noevidencefortheinteractionbetweenleptonsandquarkscarriedwithleptoquarkbosonswasobservedyet.Forleptoquarkcouplingsofelectromagneticstrength,leptoquarkswithmassesupto275-325GeVareruledout[ 42 ]. 23

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43 ]withspin1=2(anantisymmetricstateofthreeuuuquarks).Itcanhaveoneofthreevaluesred,greenorblue.Freequarkshaveneverbeenobserved,thereforeitisstronglysuggestedthatonlycolorlessstatesareallowedasrealparticles.Thecarrierofstrongcolor-conservinginteraction,abi-coloredmasslessparticleofspinonethatcarriescolorinformationfromonequarktoanotherwascalledagluon(g).GluonwasindirectlyobservedineventswiththreejetsatPETRA[ 44 ]experimentinDESY.Assumingthreecolorsonly8bi-coloredgluonsareallowed.Gluons,beingbi-coloredobjects,haveastrongcharge,therefore,theyinteractdirectlyamongthemselves.ThestronginteractioniscurrentlydescribedwithinframeworkofQuantumChromodynamics(QCD),whichisapartoftheStandardModel(moredetailsinsubsection 2.4.1 ). 45 46 ].Itwastherstsuccessfulunicationof 24

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12 ].Thewavenatureoflightwasexplainedinframeworkofthetheoryandlaterexperimentallyconrmed[ 47 ].ThetheoreticalpredictionoftheconstantspeedoflightbroketheGalileaninvarianceprincipleofclassicalmechanicsandledtoanextensionknownasthetheoryofspecialrelativity[ 48 ],whichiscompatiblewithclassicalelectromagnetism.Observationofthephotoelectriceffect[ 49 50 ]revealedthequantumnatureoflight[ 51 ].Thecarrieroftheelectromagneticcharge-conservinginteractionisanelectricallyneutralmasslessparticleofspinone,whichiscalledthephoton().Thereisonlyonetypeofphoton.Photons,beingelectricallyneutralobjects,havezeroelectricchargeanddonotinteractdirectlyamongthemselves.Photonswereexperimentallydiscoveredasradiationemittedfromradium.Thehigh-precisionquantumperturbationtheoryofinteractionsbetweenelectricallychargedparticlesbytheexchangeofphotonsiscalledQuantumElectrodynamics(QED).ElectromagneticinteractionsarecurrentlydescribedwithinuniedElectroweak(EW)theorythatisapartoftheStandardModel(moredetailsinsubsection 2.4.2 ). 25

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52 53 ].TheweakinteractioniscurrentlydescribedwithinuniedElectroweak(EW)theorythatisapartoftheStandardModel(moredetailsinsubsection 2.4.2 ).Theelectroweaktheorypredictedanadditionalneutralmassivecarrierofweakinteraction,Z0-boson.Itwasindirectlyobservedinneutralcurrentprocesses[ 54 55 ]andlaterdirectlydiscoveredwithUA1andUA2experimentsatCERN[ 56 57 ]. 58 ]whichisproportionaltothemassesoftheinteractingobjectsanddependsontheinversesquareofthedistancebetweenthem.AgreatsuccessofthetheorywasthederivationofKepler'sthreelawsofplanetarymotion,includingtheellipticalorbitsforplanets.ThemodernmathematicalnotationoftheNewton'slawisfollowing:FG=Gm1m2 59 ]in1797byHenryCavendish.Newton'slawofgravitycontinuestobeusedasanexcellentapproximationoftheeffectsofgravity.However,someastronomicalobservationswerenotinaccordwiththepredictionsofNewton'stheory.In1915AlbertEinsteindevelopedthegeneraltheoryofrelativity[ 60 ].Intheframeworkofthisgeometrictheory,gravityisaresultofspace-timebeingcurvedby 26

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2gR+g=8G c4T,whereRistheRiccicurvaturetensor,gisthemetrictensor,Risthescalarcurvature,isthecosmologicalconstant,cisthespeedoflight,andTisthestress-energytensor.TherstsuccessofthistheorywasEinstein'scalculationofperihelionprecessionofMercury[ 61 ]preciselyasastronomicallyobserved.Duringthe20thcenturythegeneralrelativitywastestedandconrmedinseveralexperiments:measurementsofdeectionoflightbytheSun[ 62 ],observationsofthegravitationalredshiftoflight[ 63 64 ],identicationsofgravitationallylensedobject(TwinQuasar)[ 65 ],testsoflighttraveltimedelay[ 66 67 ],testsoftheequivalenceprinciple[ 68 69 ],frame-draggingtests[ 70 ],andindirectdetectionofgravitationalwavesfrombinarypulsars[ 71 72 ].Gravitationalradiationobservatories[ 73 74 ]havebeenbuilttodirectlyobservegravitationalwaves.Nodetectionhasbeenmadesofar[ 75 ].In1999theSupernovaCosmologyProjectmadeanobservationoftheacceleratingexpansionoftheuniverse[ 76 ].Afavoriteexplanationofthisobservationisanon-zerocosmologicalconstant1035s2inEinstein'seldequations,whichleadstothehypothesisofdark(orvacuum)energypresentintheuniversewhichexertsnegativepressure.Themostrecentmeasurements[ 77 ]impliedavalueofdarkenergydensity=0.726whichisthefractionofthetotalmass-energydensityofaatuniverse.Duringthe20thcenturyafewapproaches(stringtheory,loopquantumgravity,etc)toquantumgravityweredeveloped[ 78 ].However,thereisnocomplete,consistentandexperimentallytestedtheorysofar.Thegraviton,ahypotheticalcarrierofgravitationalinteractionappearednaturallyinnumberofthosequantumgravitytheories.Thisparticlehasnotbeendirectlyobserved,butitisexpectedtohavespin2andmasszero. 27

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29

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12 ].AgraphicalrepresentationofSMLagrangianisshownonFigure 2-1 .Thisguredescribesallpossibletree-levelinteractionsbetweenparticlesinframeworkofSM.Solidlinesrepresentsinteractionsbetweenparticlesandforcecarriers.DashedlinesrepresentnotyetobservedinteractionbetweenmassiveparticlesandHiggsparticle.Dash-dottedlinerepresentinteractionbetweenneutrinoandHiggsparticle.FormerinteractionisnotincludedinmodernSMbuttherearestrongindications[ 9 11 ]thatneutrinosaremassiveandthisinteractionisvalid.Looplinesforg,HandWrepresentselfinteractions,i.e.3g,4g,3H,4Hand4Wcouplings. Figure2-1. Schemeoftree-levelinteractionsinStandardModel. TheSMLagrangiandependson19parametersmeasuredbyexperiments. 2i.Originallyproposedasapuremathematicaltrick[ 79 84 ],theSUSYaroseasapossiblesolutionforvariousStandardModelimperfections.First,SUSYalleviatesSMne-tuningproblemduetoreciprocalcancellationofquadraticallydivergentfermionicandbosonicloops,providedthatsupersymmetricparticleshavemassesnolargerthanafewTeV. 30

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85 87 ]. 88 ].IntheframeworkofthismodeleachSMparticleacquiresoneandonlyonesuperpartner.Eachfermion(quarkorlepton)hasasuperpartnerwithspin0calledsfermion.Byanalogy,eachSMinteractioncarrierbosonacquiressuperpartnerofspin1=2calledgaugino.Finally,itturnsoutthatonesuperpartnerfortheHiggsbosonisnotenoughtomakeMSSMmodelcomplete.TherearetwoHiggsbosons,andcorrespondinglytwoHiggssuperpartner(calledhiggsino)doubletswereintroduced.TheSMparticlesandtheirMSSMsuperpartnerstogetherwiththeirtransformationpropertiesundertheSMsymmetrygroupsaresummarizedinTable 2-4 .AfterelectroweaksymmetrybreakingisintroducedintoMSSM,chargedwinosWandhiggsinosH+u,Hdhavethesamequantumnumbersandthereforemix.Thesemixedstates(masseigenstatesofthesystem)wouldbephysicallyobservedasparticlescalledcharginos(1and2).Byconvention,massof1isconsideredtobethelightestoneoutofthesetwostates.Similarly,theneutralzinoZ0,binoB0andhiggsinosH0u,H0dare 31

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ParticlesandtheirsuperpartnerswithintheMSSMframework. Particle Gaugetransformation Superparticle spin name notation name spin 1=2 2 0 1 2 3 0 3 3 g 1 gluinos W 3 Zboson Z0 Bboson B0 1 Hu=H+uH0u 2 2 89 ]calledmSUGRAwithonlyonesuperchargewillbeassumedintherestofthiswork.Withinthismodelsupersymmetryisbrokenduetogravitationalinteractionsbetweenvisibleandhiddensectors.Thesuperpartnerofthegraviton,calledagravitino,isheavyandinteractswithotherparticlesonlygravitationally,i.e.extremelyweakly.Therefore, 32

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90 ]andthenfurtherdevelopedin[ 91 96 ].AfewexperimentalsearchesforSUSYwiththesame-chargedi-leptoneventshavebeendoneatCDFandD0experimentsatTevatroncollider[ 97 101 ].NoexcessofeventsoverSMbackgroundwasobservedinalltheseworks.Potentialtodiscoversupersymmetryineventswithsame-cargedi-leptons,jetsandmissingenergywiththeCMSdetectoratLHCinppcollisionsatp 102 104 ].Itwasdemonstrated 33

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Masslowerlimitsforsleptonsat95%C.L. slepton masslowerlimit(GeV) selectron(eR) 99.9 smuon(R) 94.9 stau(R) 86.6 thatlowmassSUSYcanbeobserveduptomassscalesof1.5TeV/c2,includingsystematiceffectsgiven10fb1ofdatacollectedatp 12 86 ]. 105 ],DELPHI[ 106 ],L3[ 107 ]andOPAL[ 108 ])collecteddatawiththeupgradedcollider(LEP2)atenergiesrangingbetweenp 109 112 ].TheL-sleptonswereassumedtobebeyondthereachoftheexperimentsbecause,ingeneral,thecrosssectionforR-sleptonsissmallerthanforL-sleptons.Chargedsleptonsweresearchedassumingfollowingdecayl!l01,wheretheneutralino(01)istheLSPandescapesdetection.ConstraintshavebeenderivedinthecontextoftheMSSM.Thecombinationoftheexperimentsshowsnoevidenceforanexcessofcandidatescomparedtotheestimatedbackground.Theexpectedandobservedexclusioncurvesat95%CondenceLevel(C.L.)inthe(sleptonmass,neutralinomass)planeisshowninFigure 2-2 (left).LowerlimitsforsleptonmassesaresummarizedinTable 2-5 .ThelimitonmeRisbroadestbecausethecrosssectionforselectronpairproductionatLEP2wasgreaterthanthecrosssectionsforsmuonorstaupairsproduction. 34

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Exclusionlimits(at95%C.L.)onsparticlemassesfromthenon-observationofanysignalexcessoverbackgroundinLEP2experiments.Left:Masslowerlimitforsleptons(mlR).Right:Masslowerlimitforcharginos(01). AllfourLEPexperimentsanalyzedthechargino(+1)decaysintoleptons,leptonsplusjets,andjets[ 113 ].Theresultsfromthesechannelswerethencombined.CrosssectionsandbranchingratioshavebeencalculatedintheframeworkoftheMSSM.Thecombinationoftheexperimentsshowsnoevidenceforanexcessofcandidatescomparedtotheestimatedbackground.Obtainedexclusionlimits(at95%C.L.)inthe(sneutrinomass,charginomass)planeisshownin 2-2 (right)forthecombinationofthe208GeVdata.Theaveragelowerboundoncharginomassis103.5GeV. 114 116 ]andD?[ 117 119 ])collecteddatawithupgradedcollideratcenterofmassenergyp 120 121 ].Analyzeddatashowsnoevidenceforanexcessofcandidatescomparedtotheestimatedbackground.Obtainedexclusionlimits(at95%C.L.)inthem0-m1=2andmq-mgplanesareshowninFigure 2-3 forD?andinFigure 2-4 forCDFexperiments. 35

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Theredregionsshowtheareas(left:insquarkandgluinomassesplane;right:inm0-m1=2plane)excluded(at95%C.L.)byD?experimentatTevatronwith2.1fb1ofdatafromthenon-observationofanysignalexcessoverbackgroundintheframeworkofmSUGRAassumingR-parityconservation[ 120 ].Exclusionsbyotherexperimentsarealsoshownforcomparison. Figure2-4. Theredregionsshowtheareas(left:insquarkandgluinomassesplane;right:inm0-m1=2plane)excluded(at95%C.L.)byCDFexperimentatTevatronwith2.0fb1ofdatafromthenon-observationofanysignalexcessoverbackgroundintheframeworkofmSUGRAassumingR-parityconservation[ 121 ].Exclusionsbyotherexperimentsarealsoshownforcomparison. 36

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122 124 ].Analyzeddatashowsnoevidenceforanexcessofcandidatescomparedtotheestimatedbackground.Obtainedexclusionlimits(at95%C.L.)inthem0-m1=2planeareshowninFigure 2-5 (leftCDF,rightD0). Figure2-5. Theblueregionsonleftplotshowtheareas(inm0-m1=2plane)excluded(at95%C.L.)byCDFexperimentwith3.2fb1ofdatafromthenon-observationofanytri-leptonsignalexcessoverbackgroundintheframeworkofmSUGRAassumingR-parityconservation[ 123 ].Thegreenregionsonrightplotshowtheareas(inm0-m1=2plane)excluded(at95%C.L.)byD?experimentwith2.3fb1ofdatafromthenon-observationofanytri-leptonsignalexcessoverbackgroundintheframeworkofmSUGRAwithR-parityconservation[ 124 ]. 37

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12 ].TheexperimentalsetupforprospectiveSUSYsearch,asdescribedinChapter 4 ,isacolliderexperimentandconsistsofanacceleratorLargeHadronCollider(LHC)[ 125 126 ]andadetectorCompactMuonSolenoid(CMS)[ 127 128 ].ThemeasurementofefciencyofndingmuontracktriggerprimitivesinCMSCathodeStripChambers,asdescribedinChapter 5 ,hasbeendonewithcosmicraysdetectedbytheCMSMuonEndcapSystemandthereforewasanon-colliderexperiment.Ageneralreviewofnon-colliderinstrumentsandmethods(e.g.cosmicrayexperiments,neutrinooscillationmeasurements,searchesfordouble-betadecay,darkmattercandidates,magneticmonopoles,etc.)iswellbeyondthescopeofthisworkandcanbefoundelsewhere[ 12 ]. 3.2.1PhysicsRequirementsTheStandardModel(SM)ofparticlephysicshasbeentestedwithhighprecisionduringthepastfewdecades.Yetitisconsideredtobeaneffectivetheoryonlyuptoroughly1TeV.Alsoexperimentalconrmationoftheelectroweaksymmetrybreaking(Higgs)mechanismatanenergyscalebelow1TeVisstillrequiredtobefoundforthemathematicalconsistencyoftheSM.Thereareseveralalternativemodels(supersymmetry,extradimensions,etc.)beyondSMthatmaydescribenature.Mostofthempredictnewparticlesorphenomena 38

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39

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3-1 (left).TheLHCisinstalledintheexisting26.7kmtunnelthatwasconstructedfortheCERNLEPmachine.Thetunnelliesbetween45mand170mbelowthesurfaceonaplaneinclinedat1.41%slopingtowardslakeLemanwithrespecttothehorizontal,thusgivingheightdifferencesofupto120macrossthetunneldiameter.Thetunnelgeometrywasoriginallydesignedfortheelectron-positronmachine,andtherewereeightcrossingpointsankedbylongstraightsectionsforRFcavitiesthatcompensatedforthehighsynchrotronradiationlosses.TheLHCbeingaprotonmachinedoesnothavethesamesynchrotronradiationrateandwouldideallyhavelongerarcsandshorterstraightsectionsforthesamecircumference.ButreusingtheLEPtunnelanditsinjectionchainwasacostsavingsolutionthatstronglyinuencedthedecisiontobuildtheLHCatCERN. Figure3-1. TheLHCgeographicallocationonmap(left)andtunnelscheme(right). Itwasdecidedtouseonlyfourofthepossibleeightinteractionregionsandtosuppressbeamcrossingintheotherfourtopreventunnecessarydisruptionof 40

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41

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1TheTouschekeffectisasinglescatteringeffectwhichleadstotheimmediatelossofthecollidingparticlesduetotransformationofasmalltransversemomentumintoalargelongitudinalmomentum.2Theintra-beameffectisamultiplescatteringwhichleadstodiffusioninallthreedirectionsandchangesthebeamdimensions.3Commonunitofintegratedluminosityisinversebarn(symbolb1).Barnisaunitofareadenedas1024cm2.Notethat1fb1=1039cm2. 42

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3-2 (left).Thismakesitextremelydifculttoinstalltwoseparateprotonringsinthetunnel.Thehardlimitonspaceledtotheadoptionofthetwo-in-one(ortwin-bore)superconductingdipolemagnetsthatconsistoftwosetsofcoilsandbeamchannelswithinthesamemechanicalstructureandcryostatwithmagneticuxcirculatingintheoppositedirectionsthroughthetwochannels.Thedisadvantageofthetwin-boredesignisthattheringsaremechanicallyandmagneticallycoupled,whichaffectsexibility.Thetransversecross-sectionoftheLHCcryodipoleisshowninFigure 3-2 (right). Figure3-2. Transversecross-sectionsoftheLHCtunnel(left)andcryodipole(right). TheLHCringaccommodates1232maindipoles:1104inthearcand128inthedispersionsuppressionregions.Theyallhavethesamebasicdesign.Adipolecoldmasshasanoveralllengthofabout16.5m,adiameterof570mm(atroomtemperature),andamassofabout27.5ton.Thecoldmassiscurvedinthehorizontalplanewithanapicalangleof5.1mrad,correspondingtoaradiusofcurvatureofabout 43

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3-1 (right).ThecryogenicsystemhasvecryogenicislandsataccessPoints1,2,4,6and8,whereallrefrigerationandancillaryequipmentisconcentrated.Equipmentatgroundlevelincludeselectricalsubstations,warmcompressors,cryogenicstorage(heliumandliquidnitrogen),coolingtowers,andcoldboxes.Undergroundequipmentincludeslowercoldboxes,1.8Krefrigerationunitboxes,interconnectinglines,andinterconnectionboxes.Eachcryogenicislandhousesoneortworefrigerationplantsthatfeedoneortwoadjacenttunnelsectors,requiringdistributionandrecoveryofthecoolinguidsoverdistancesof3.3kmunderground.Thetotalamountofrequiredsuperuidheliumis96ton.Foranormalcooldownofasector,the600kWpre-coolerwilluseamaximumof1260tonofliquidnitrogen. 44

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3-3 .Hydrogengasisfedintoaduoplasmatroncathodechamberwithelectrons.InthechamberthehydrogenatomsdissociateandformaH+plasmaconnedwithinthemagneticeld.Theplasmaisconstrictedbyacanalandextractedthroughtheanodeintoanexpansionchamberwhereaprotonbeamof300mAintensityisformed.The 45

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SchematicrepresentationoftheLHCinjectorchain(dimensionsnotproportionaltomachinesrealsize). LHCduoplasmatronoperatesat92keV.ThenprotonsentertheRFquadrupolethatprovidestransversefocusingofthebeamandacceleratesittoenergyof750keV.Thenextstageisamulti-chamberresonantRFcavityacceleratorcalledLinac2.Itacceleratesabeamofcurrent180mAupto50MeV.Italsoshapestheprotonbeamintoshortpulsesof30slengthandlowtransverseemittanceof1.2m.TheProtonSynchrotronBooster(PSB)followsprotonbeamacceleration.ThebeamlinetothePSBfromtheLinacis80mlong,and20quadrupolemagnetsfocusthebeamalongtheline.ThePSBbooststheprotonsupto1.4GeVandinjectsthemintotheProtonSynchrotron(PS).ThePShasbeenupgradedfor40and80MHzofRFoperationfortheLHCandallowstoaccelerateprotonsupto28GeV.ThePSisalsoresponsibleforprovidingthe25nsbunchseparationfortheLHC.ConvertedforoperationwiththeLHC,theSPSboostsprotonsupto450GeVfortheLHCinjection.NotethatSPSwastheinjectorfortheLEPsystem,andtheinjectionsystemwasupgradedaswellastheRFsystems.SPSisfullyLHCdedicatedduringlls(1-2timesperday).Alsoitservesforotherexperimentsasasourceofprotons. 46

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47

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48

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129 ].Assumingcontinuousround-the-clockrunningofLHC,itisexpectedtoconsume130GWhofenergypermonth.Followingmostrecentschedule[ 130 ],theLHCafterstartupwillruncontinuouslyfor18-24monthshencetheenergyconsumptionisestimatedtobe1.6TWhperyear.Forcomparison,thetotalelectricenergyconsumptionofthecityofGainesville(Florida,US)is5.4TWhperyear[ 131 ]whichis3timesmorethanLHCconsumption.Basedoncurrentaverageelectricityprice(3c/kWh)theoneyearofLHCrunningwouldresultin50Mdollarsofelectricbill. 3.3.1GeneralDescriptionTheCompactMuonSolenoid(CMS)experimentisoneoffourdetectorsbuiltatcrossingsitesoftheLHCbeams,andisoneoftwogeneralpurposedetectors(theotheristheATLASdetector)whichhavebeendesignedtoexploitthephysicsopportunitiespresentedbytheLHC.TheCMSislocatedatPoint5asshowninFigure 3-1 (right).TherearethefollowingrequirementsfortheCMSphysicsprogram: 49

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AperspectiveviewoftheCMSdetector. 3-4 anditincludesfollowingsystems: 50

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3-5 .AllsystemsoftheCMSdetectorarebrieyreviewedinthefollowingsubsections.AdetaileddescriptionoftheCMSdesigncanbefoundelsewhere[ 127 128 ]. Figure3-5. PropagationofdifferentparticlesthroughtheCMSdetector. 3-6 .Asviewedfromtheinteractionpoint(IP),azimuthalangleincreasesintheconventionalway,i.e.clockwiseforthe+zendcapandcounterclockwiseforthezendcap. 51

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OverallCMScoordinatesystem. 52

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3-4 ).TheCMSdetectorhasamodulardesignandcanbereassembled.TheelementsoftheCMScanbemovedbyastrandjackinghydraulicsystemthatensuressafeoperationonthe1.23%inclinedoorofthecavern.Themaximummovementspossibleinthecavernare11m.Toeasilyaligntheyokeelements,aprecisereferencesystemofabout70pointswasinstalledinthesurfaceassemblyhall.Alltheelementsarepre-positionedwithina5mmtoleranceandthenalignedwithanaccuracyof2mmwithrespecttotheidealaxisofthecoil. 53

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3-7 .Thepixeldetectoriscompletedby2disksinendcaps.Thestriptrackerhas3plus9disksoneachsideofthebarrel,extendingtheacceptanceofthetrackeruptoapseudorapidity5of<2.5. Figure3-7. Left:perspectivedrawingoftheCMStracker.Right:schematiccrosssectionthroughtheCMStracker.Eachlinerepresentsadetectormodule. Thepixeldetectordeliversthreehighprecisionspacepoints(hits)oneachchargedparticletrajectory.Intotalthepixeldetectorcoversanareaofabout1m2,has1440modulesand66millionpixels.Technologicallythepixelsconsistofhighdosen-implantsintroducedintoahighresistancen-substrate(doublesidedn-on-nconcept).Thesensortemperatureismaintainedatabout1015Ctoreducetheeffectsofradiationdamage;liquidphasecoolingwithC6F14isusedwithtotalowrateof1litre/s.Theparticledetectioninefciency(duetoread-outarchitecturedataloss)hasbeenmeasuredinahigh-ratepionbeam.Itreaches0.8%,1.2%and3.8%respectivelyforthethreelayersatLHCdesignluminosityof1034cm2s1and100kHzrate.Thepixelsystemisinsertedasthelastsub-detectorofCMSafterthecentralsectionofthebeampipehasbeeninstalledandbakedout.Thissiliconstriptrackerdeliversatleastninehitsinthefullrangeofacceptancejj<2.4withatleastfourofthembeingtwo-dimensionalmeasurements.Intotalthesiliconstriptrackercoversanareaofabout198m2,has15148modules,24244sensors 54

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3-8 Figure3-8. Left:perspectivedrawingoftheCMSelectromagneticcalorimetershowingthearrangementofcrystalmodules,supermodulesandendcaps,withthepreshowerinfront.Right:transversesectionthroughtheCMSelectromagneticcalorimeter,showinggeometricalconguration. 56

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3-9 (left).Thehadronbarreldetector(HB)isasamplingcalorimetercoveringthepseudorapidityrangejj=1.3.TheHBconsistsof36identicalazimuthalwedgeswhichformthetwo 57

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Left:thehadroncalorimetertowersegmentationinthe(r;z)planeforone-fourthofthebarrel(HB),endcap(HE)andouter(HO)detectors.Theshadingrepresentstheopticalgroupingofscintillatorlayersintodifferentlongitudinalreadouts.Right:photoofassembledhadroncalorimeterhalf-barrel. half-barrels(HB+andHB).Thewedgesareconstructedoutofatbrassabsorberplatesalignedparalleltothebeamaxis.Eachwedgeissegmentedintofourazimuthalanglesectors.Theinnermostandoutermostplatesaremadeofstainlesssteelforstructuralstrength.Theplasticscintillatorisdividedinto16sectors,resultinginasegmentation(;)=(0.087;0.087).Thecrackbetweenthewedgesislessthan2mm.Theabsorberconsistsofa40-mm-thickfrontsteelplate,followedbyeight50.5-mm-thickbrassplates,six56.5-mm-thickbrassplates,anda75-mm-thicksteelbackplate.Thetotalabsorberthicknessat90is5.82interactionlengths(I).TheHBeffectivethicknessincreaseswithpolarangleas1=sin,resultingin10.6Iatjj=1.3.TheelectromagneticcrystalcalorimeterinfrontofHBaddsabout1.1Iofmaterial.Thehadroncalorimeterendcaps(HE)coverasubstantialportionoftherapidityrange,1.3
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132 134 ]iscathodestripchambers(CSC)[ 135 136 ],theconceptofwhichwasrstproposedbyG.Charpakmorethan30yearsago[ 137 ].TheCMSCSCsdetectmuontracksinthepseudorapidityrange0.9
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3-10 (right). Figure3-10. Left:Aschematicquarter-viewoftheCMSdetector(CSCsoftheEndcapMuonsystemarehighlighted;MEstandsforMuonEndcapchambers).Right:AphotooftheME+2diskanditsstationsofcathodestripchambers. TheCMSCSCsarecomprisedof6planesofanodewiresinterleavedbetween7trapezoidalcathodepanels(Figure 3-11 (left)).MostoftheCSCshaveagasgapbetweenthecathodepanelsofabout1cm.Anelectronavalanchecausedbyamuontraversingagasgapproducesasignalontheanodewires(Figure 3-11 (righttop))whichinducesadistributedchargeonthecathodestrips(Figure 3-11 (rightbottom))[ 132 137 ].Byreadingoutsignalsfromwiresandstrips,CMSCSCsmeasure2muoncoordinates:thedistancefromthebeamlinerandtheazimuthalangleineachofthe6planes.AsamuongoesthroughtheCMSdetectorinthestrong(4T)magneticeldproducedbythecentralsolenoid,thechangeinits-coordinatesallowsitstransversemomentumtobemeasured.Hence,therequirementsontheprecisionofmeasuring-coordinatesaremorestringentthanthoseforr-coordinatemeasurements.Wiresrunazimuthallyanddenetheycoordinateofthemuontrackinthechamber'slocalcoordinatesystem(Figure 3-11 (left)).Forreadoutpurposes,thewiresarearrangedintogroups.Eachgroupconsistsofvetosixteenwiresand 60

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3-12 (left).Stripsaremilledonthecathodepanelsandrunlengthwiseataconstantswidth.Theangularstripwidthsvariesfordifferentchambertypesfrom2mrad,whilethespatialwidthvariesfrom4mm,dependingonthechambertypeandlocalchamberycoordinate.Bycomparingsignalamplitudesonnearbystrips,theCSCelectronicsquicklymeasurethemuonxcoordinatetoaprecisionofhalfastripwidth[ 138 ].Thisinformation,theso-calledcathodecomparatorhits,isusedbythemuonLevel-1trigger.Stripsignalsarealsodigitizedby12-bitADCs.Byinterpolatingsuchdigitizedsignalsinall6planes,amuon'sx-coordinateinachamberismeasuredwithaprecisionof75m(cf.atypicalsagittaofamuonwithatransversemomentumpT=100GeVasmeasuredbetweenIP,ME1,andME2stationsisabout4mm[ 132 ]).ThisinformationisavailablefortheHigh-LevelTrigger(HLT)andofineanalyses.Figure 3-12 (right)illustratesapatternofinducedchargesonstripsandhalf-stripbitscreatedbyamuon.Detailsonchamberlocationsandtheirinternalgeometricalparametersaregiveninreference[ 132 ]. 61

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Left:SchematicviewofaCMScathodestripchamber.Thecutoutinthetoppanelallowsonetoseetheradialfan-shapedcathodestripsandanodewiresrunningacrossthestrips(onlyafewwiresareshown).Right:AnillustrationoftheCSCoperationprinciple.Anelectronavalancheresultingfromamuontraversingagasgapproducesasignalontheanodewireswhichinducesadistributedchargeoncathodestrips. Figure3-12. Left:ApatternofwiregrouphitscreatedbyamuonpassingthroughaCSC.Right:Apatternofinducedchargesonstripsandcomparatorhalf-striphitscreatedbyapassingmuon. chambersineachstationareseparatedasmuchaspossibletoachievethebestangularresolution.Thedriftcellsofeachchamberareoffsetbyahalf-cellwidthwithrespecttotheirneighbortoeliminatedeadspotsintheefciency.Thisarrangementalsoprovidesaconvenientwaytomeasurethemuontimewithexcellenttimeresolution,usingsimplemeantimercircuits,forefcient,standalonebunchcrossingidentication.Thenumberofchambersineachstationandtheirorientationwerechosentoprovidegoodefciency 62

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Figure3-13. SchematiclayoutoftheCMSmuondrifttubeschambersononeofthe5barrelwheels. 63

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Figure3-14. Left:SchematiclayoutofRPCstationRBononeofthe5barrelwheels.Center:schematic(r;)layoutofRPCstationRE2onthebacksideoftherstendcapyoke.Right:photoofRPCstationRE2onthebacksideoftheYE-1yoke.Theinnerringhasbeenstagedandisabsenthere. 64

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3-15 .TheDAQsystemmustsustainamaximuminputrateof100kHz,foradataowof100GByte/scomingfromapproximately650datasources,andmustprovideenoughcomputingpowerforasoftwareltersystem,theHLT,toreducetherateofstoredeventsbyafactorof1000.InCMSalleventsthatpasstheLevel-1(L1)triggeraresenttoacomputerfarm(EventFilter)thatperformsphysicsselectionsusingfasterversionsoftheofinereconstructionsoftware,toltereventsandachievetherequiredoutputrate. Figure3-15. ArchitectureoftheCMSDAQsystem. TheCMSofinecomputingsystemmustsupportthestorage,transferandmanipulationoftherecordeddataforthelifetimeoftheexperiment.Thesystemacceptsreal-timedetectorinformationfromthedataacquisitionsystemattheexperimentalsite;performspatternrecognition,eventltering,anddatareduction;supportsthephysicsanalysisactivitiesofthecollaboration.Thesystemalsosupportsproductionanddistributionofsimulateddata,andaccesstoconditionsandcalibrationinformationandothernon-eventdata. 65

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3.4.1TheCMSResultswithCosmicMuonsBuildingacomplexsystem,suchastheCMSdetector,requirednumerousteststobedone.Thenaturalwaytomakesuchtestsistousemuonsfromcosmic-rayinteractionsintheatmosphere.TheCMSdetectorunderwentafewmajortestsdescribedbelow.AlltheinstallationandcommissioningoftheCMShadbeendoneinasurfacehallbeforeallthedisksandwheelswereloweredtoLHCcavernatPoint5.Operationofallthesub-detectorsandsub-systemsoftheCMStogetherwasdoneinFall2006duringMagnetTestandCosmicChallenge(MTCC06).Theparticipatingsystemsincludeda60sectorofthemuonsystem,bothintheBarrelandEndcaps.Theinnertrackingsystem,electromagneticandhadroncalorimeterparticipateinthetestatleastatthe10%level.Otherexercisesincludedmaneuveringlargeelementsofthedetector,operationinmagneticeld,coherentrunningofsubsystems,operationalandsafetyprocedures.OneoftheresultsofMTCC06,themeasurementofefciencyofndingmuontracktriggerprimitivesincathodestripchambers,ispartofthisthesisanddescribedinChapter 5 .OthermajorresultsandlessonslearnedduringMTCC06arereviewedin[ 139 ].AftertheloweringoftheCMSdetectordowntotheLHCcavernatPoint5inFall2008amonth-longdata-takingrunwasperformed.ItwascalledCosmicRunAt(almost)FourTesla(CRAFT08).TheaimofthetestwastoruntheCMScontinuouslyasacompleteexperiment,24hoursaday,togainoperationalexperienceevenwithoutLHCbeams.Datafrom300millioncosmicmuons(includingmorethan7milliontracksinthestriptrackerandaround75000tracksinthepixeltracker)wererecordedwiththesolenoidatitsoperatingpointof3.8Tfordetaileddetectorstudies. 66

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Left:standalonecosmicmuoncrossingtheCMSdetectorfromtoptobottom,recordedinCRAFT08,leavingsignalsinthemuonsystem,andcalorimeters.Right:globalcosmicmuoncrossingtheCMSdetectorfromtoptobottom,recordedinCRAFT08,leavingsignalsinthemuonsystem,trackingdetectorsandcalorimeters[ 140 ]. OneoftheresultofCRAFT08wasthemeasurementoftheuxratioofpositiveandnegativecosmicmuons.TheexcellentperformanceoftheCMSdetectoralloweddetectionofmuonsinthemomentumrangefrom3GeV/cto1TeV/c.TheeventdisplaysofthecosmicmuonscrossingtheCMSdetectorareshowninFigure 3-16 .Formuonmomentabelow100GeV/ctheuxratioismeasuredtobeaconstant1.27660.0032(stat)0.0032(syst),themostprecisemeasurementtodate.Furtherdetailsonthemeasurementcanbefoundelsewhere[ 140 ].OthermajorresultsandlessonslearnedduringCRAFT08arereviewedin[ 141 ]. 67

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3-17 .ThisluminosityisenoughtolookintoQCDprocesseslikeJ=production.ItalsoallowstoseerstWandZbosonevents. Figure3-17. TheluminosityintegratedbythefourLHCexperiments. 142 ].AlsoBose-Einsteincorrelationshavebeenmeasured[ 143 ].Thesignalwasobservedintheformofanenhancementofpairsofsame-signchargedparticleswithsmallrelativefour-momentum.Andnally,inclusivecharged-hadrontransverse-momentumandpseudorapiditydistributionswerestudied[ 144 ]. 68

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3-18 )ininvariantmassdistributionscorrespondingtoJ=!andJ=!eehavebeenobserved[ 145 ].Indi-electronchannellowpTelectronswereselected.Samesignandoppositesigncombinationswereseparatelyplotted.Binnedlikelihoodtofagaussianandconstantvalueinthemassrange1.5.5GeVwasperformed.Claimedsignalistheintegralofthegaussian;backgroundquotedin2.5aroundthemeanvalue.Inthedi-muonchannel,lowpTmuonswereselected.ExtendedmaximumlikelihoodtswereperformedwithanexponentialforthebackgroundandaCrystalBallfunction7forthesignalinordertoaccountforradiativetails.Claimednumberofsignaleventsis123047.TheWandZinclusiveproductionatp 146 ].TheeventswithanisolatedmuonofgoodqualitywithpT>25GeVaccompaniedbyacoplanartrack-correctedmissingtransverseenergywereselectedasW!candidates.Eventswithtwoormoremuonswererejected.AneventdisplayofaselectedW!candidateisshowninFigure 3-19 (left).DistributionoftransversemassofselectedW!eventsisshowninFigure 3-19 (right).ThecrosssectionsinMonteCarloonthisplotarenormalizedtoMCFMNLOpredictionsusingMSTW08NLOPDFsandtotheestimatedCMSluminosityof16nb1forthegoodrunsandluminositysectionsconsideredindata.SignalshapeisNLO(POWHEG).Backgroundsinclude:Z!(NLO,POWHEG),W!(PYTHIA),Z!(PYTHIA),andtt(PYTHIA).TheQCDbackgroundisPYTHIAleadingorderprocesses.TheeventswithisolatedelectronsofgoodqualitywithelectromagneticclusterET>10GeVaccompaniedbymissingtransverseenergy,withanadditionalcuton 69

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3-20 (left).DistributionoftransversemassofselectedW!eeventsisshowninFigure 3-20 (right).BackgroundprocessesweregeneratedwithPYTHIAinleadingorder.ThesignalwasrescaledtotheNLOcrosssectionandnormalizedtointegratedluminosity.TheeventswithtwoisolatedmuonswithpT>20GeVwereselectedasZ!candidates.Thenumberofselectedeventsis5for16nb1ofintegratedluminosity.AneventdisplayofaselectedZ!candidateisshowninFigure 3-21 (left).DistributionoftheinvariantmassofselectedZ!eventsisshowninFigure 3-21 (right).ThecrosssectionsinMonteCarloonthisplotarenormalizedtoMCFMNLOpredictionsusingMSTW08NLOPDFsandtotheestimatedCMSluminosityof16nb1forthegoodrunsandluminositysectionsconsideredindata.Backgroundsinclude:W!,andtt.TheQCDbackgroundisPYTHIAleadingorderprocesses.TheeventswithtwoisolatedelectronsoflooseidenticationqualitieswithelectromagneticclusterET>10GeVwereselectedasZ!eecandidates.Numberofselectedeventsis5for16.6nb1ofintegratedluminosity.AneventdisplayofaselectedZ!eecandidateisshowninFigure 3-22 (left).ThedistributionofinvariantmassofselectedZ!eeeventsisshowninFigure 3-22 (right).BackgroundprocessesweregeneratedwithPYTHIAinleadingorder.ThesignalwasrescaledtotheNLO(POWHEG)crosssectionandnormalizedtointegratedluminosity. 70

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Left:InvariantmassdistributionoftheJ=!events.Right:InvariantmassdistributionoftheJ=!eeevents. Figure3-19. Left:EventdisplayoftheW!candidate.Right:TransversemassdistributionoftheW!events. Figure3-20. Left:EventdisplayoftheW!ecandidate.Right:TransversemassdistributionoftheW!eevents. 71

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Left:EventdisplayoftheZ!candidate.Right:InvariantmassdistributionoftheZ!events. Figure3-22. Left:EventdisplayoftheZ!eecandidate.Right:InvariantmassdistributionoftheZ!eeevents. 72

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102 104 ]inCMS.ThisworkextendsthoseearlierstudiestoLHCenergiesp 147 149 ].Similarsensitivitiesarereported.EventhoughweperformourstudywithinthecontextofmSUGRA,whichisapopular4-parametermodelofsupersymmetry,ourmethodisnotspecictothemSUGRAframeworkandappliesequallywellinothercontexts.Indeed,oursignatureisquitegenericinsupersymmetry:themissingtransverseenergyisanecessaryconsequenceofR-parity,thejetsresultfromthedecaysofcoloredsuperpartners(squarksandgluinos)whichareexpectedtobepredominantlyproducedattheLHC,andpromptleptonscanresultfromthedecaysofcharginos,neutralinosorsleptonswhichmayappearinthelaterstagesofthesquarkandgluinodecaychains(Figure 4-1 ).TherequirementthattheleptonshavethesamechargeallowsforanefcientsuppressionoftheSMbackgrounds,andatthesametimeretainsmuchof 73

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Figure4-1. Anexampleofdiagramshowingasquark-gluinoproductioneventfollowingcascadedecays,resultingintwosame-chargemuons. CurrentexclusionlimitsonmSUGRAfromLEP(combinedresultforalldetectors)andTevatron(CDFdetector)experimentsareshowninFigure 4-2 .TherearealsolimitationsonthemSUGRAfromnon-colliderexperiments(darkmatterdensity,b!s,g2)thatarenotshownandcanbefoundelsewhere.AdetaileddescriptionoftheCompactMuonSolenoid(CMS)experimentcanbefoundelsewhere[ 128 ]. 4.2.1AnalysisFlowThisworkusestheofcialfullysimulated(FullSim)CMSSummerandFall2008datasets(p 74

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TheLM0mSUGRAsampleusedforoptimizationisshownasstar(?)inthem0-m1=2parametersplane.OtherofcialCMSmSUGRAbenchmarkpointsareshownassolidcircles().OthermSUGRAparameters(tan,sign,andA0)arexedforeachpointasshowninTable 4-1 .ExcludedregionsformSUGRAwithtan=3,>0,andA0=0byparticleexperiments(LEPmassesofcharginoandsleptonsshadedarea,CDFdirectsearchforsuperpartnerswithtrileptonsignaturesolidbluearea)arealsoshown.Referencelinesofequalmassesfordifferentsuperparticlesareplotted. wereproducedwithvariousMonteCarlo(MC)generationsoftwares(seedetailsinsubsections 4.2.2 and 4.2.3 ).CMSSoftware(CMSSW)wasusedtogeneratestableparticles,tosimulatethepassageofparticlesthroughtheCMSdetectoranditsresponse,todigitizeallsimulatedhitsandtoreconstructthedigitizedinformation.CMSSW2.2.1wasusedforallSMbackgroundssamplesandCMSSW2.2.3wasusedforallSUSYsignalsamples.AllreconstructeddatasetswereprocessedwithCMSPhysicsAnalysisTools(PAT)integratedintoCMSSW2.2.9.PATobjectswereusedintheanalysistoselectSUSYsignalevents. 75

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150 ]intheframeworkoftheMinimalSupersymmetricStandardModel(MSSM),includinghigherordercorrections.DecaywidthsandbranchingratiosofsupersymmetricparticleswerecalculatedbyaprogramSDECAY1.2[ 151 ].TheseprogramswereinterfacedtogetherbyapackageSUSY-HIT[ 152 ].LeadingordercrosssectionsthenderivedbyPYTHIA6[ 153 ].ThesameprogramwrappedintoCMSSWwasusedtogeneratethemSUGRAsignaldatasetsandtheCTEQ6L1[ 154 ]librarywasusedforthepartondistributionfunctions.Table 4-1 displaysthedifferentparametersforallfullysimulatedandreconstructedmSUGRApointsusedinthisanalysis.ThereareratioofthevacuumexpectationvaluesofthetwoHiggselds(tan);signoftheunmixedhiggsinomass(sign);higgs-squark-squarktrilinearcouplingconstant(A0);universalscalar(m0)andgaugino(m1=2)masses.Massesofcorrespondingsquarksandgluinoforeverybenchmarkpointsarealsoreported.SeeFigure 4-2 forrelativelocationofthebenchmarkpointsinthem0-m1=2parametersplane. Table4-1. InputparametersoffullysimulatedandreconstructedCMSmSUGRAbenchmarkpoints. SUSY tan (GeV=c2) (GeV=c2) (GeV=c2) (GeV=c2) LM0 10 -400 + 200 160 415 409 LM1 10 0 + 60 250 552 603 LM2 35 0 + 185 350 770 827 LM3 20 0 + 330 240 619 597 LM4 10 0 + 210 285 653 687 LM5 10 0 + 230 360 800 851 LM6 10 0 + 85 400 850 932 ConsideringLHCcenterofmassenergyp 4-2 :numberofgeneratedMCeventsandequivalentintegratedluminosity;expectednumberofeventsandeventweightfor100pb1ofintegratedluminosity. 76

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NumberofgeneratedMCeventsoffullysimulatedandreconstructedCMSmSUGRAbenchmarkpoints. SUSY #events equivalentRL MC (pb1) #events eventweight LM0 202,686 1.2E+03 16,601 0.082 LM1 104,800 4.7E+03 2,246 0.021 LM2 130,400 3.9E+04 335 0.0026 LM3 153,000 9.0E+03 1,705 0.011 LM4 110,400 1.2E+04 940 0.0085 LM5 171,600 6.4E+04 268 0.0016 LM6 134,400 7.7E+04 174 0.0013 Fastgenerationandsimulation(FastSim)wasperformedforbothLHCcenterofmassenergies(p 4-2 )forxedmSUGRAparameters:tan=3,>0andA0=0.DatacardssuppliedbytheSUSY/BSMgroupwereusedtogenerateadditionalmSUGRAdatasets.ThesoftwarepackageusedtogeneratesignalsampleswasPYTHIA6.ThemSUGRAspectrumofSUSYmassesandmixingwascalculatedbySOFTSUSY.CTEQ6L1wasusedforthepartondistributionfunctions.TheoutputleswereprocessedbyusingCMSSWforfastdetectorsimulation,reconstruction,andtheproductionofPATsamplesforanalysis.Pointsweregeneratedonacoarsegridwithm0=10GeV/c2andm1=2=10GeV/c2,startingfromthepointm0=0GeV/c2,m1=2=150GeV/c2.Forvalidationpurposes,sampleoftheLM0mSUGRAbenchmarkpointatp D thatFullSimandFastSimsamplesareinverygoodcoincidence.Next-to-leadingordercrosssectionswerecalculatedforeachFastSimSUSYsampleusingPROSPINOsoftware[ 155 ].Thecalculatedk-factorsandNLOcrosssectionsforLHCcenterofmassenergyp 4-3 .CrosssectionsinleadingLOandnext-to-leading 77

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4-3 Figure4-3. Next-to-leadingordercrosssections(left)andk-factors(right)forLHCcenterofmassenergyp Table4-3. CrosssectionsofCMSmSUGRAbenchmarkpoints. scale SUSY (pb) (pb) (pb) (pb) LM0 110 1.51 166 38.9 1.48 57.7 2.88 LM1 16.1 1.40 22.5 4.89 1.39 6.79 3.31 LM2 2.42 1.38 3.35 0.603 1.36 0.819 4.09 LM3 11.8 1.45 17.1 3.44 1.42 4.89 3.49 LM4 6.70 1.40 9.40 1.88 1.36 2.56 3.67 LM5 1.94 1.38 2.68 0.473 1.33 0.631 4.24 LM6 1.28 1.36 1.74 0.31 1.31 0.405 4.30 4.2.3.1ProductionofQCDWhileQCDmulti-jeteventsdonotintrinsicallyinvolveFeynmandiagramsproducingnalstatessimilartothetopologicalsignaturerequiredbythisanalysis,owingtoitsenormouscrosssection(seeTable 4-4 ),QCDcanproducenalstatecongurationswhichareexperimentallysimilar.Inadditiontomultiplejets,signicantmissingETcanbefakedbymis-measurementofjetenergiesandmuonscanbeproducedinheavyavoreventsorfakedinseveralwayssuchaspunch-through. 78

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CrosssectionsofQCD(bb)backgroundsamplesindifferentHTranges. scale QCD(bb) (pb) (pb) 100
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CrosssectionsofSM(noQCD)backgroundsamples. scale SM (pb) (pb) (pb) (pb) 317 1.31 415 95 1.74 165 2.52 40000 1.07 42761 24170 1.20 29040 1.47 3700 1.14 4202 2400 1.17 2810 1.50 44.8 1.59 71.4 28 1.53 42.9 1.67 17.40 1.80 31.4 10.5 1.74 18.3 1.72 7.1 1.39 9.9 4.3 1.37 5.9 1.68 Table4-7. NumberofgeneratedMCeventsoffullysimulatedandreconstructedSM(noQCD)backgroundsamples. SM #events equivalentRL MC (pb1) #events eventweight 946,644 3.0E+03 41,500 0.044 9,338,174 2.3E+02 4,276,120 0.458 1,262,816 3.4E+02 420,200 0.3327 204,722 4.6E+03 7,140 0.035 246,550 1.4E+04 3,140 0.0127 199,810 2.8E+04 990 0.0050 4-6 ).Atotalofapproximately9.3millioninclusiveWand1.3millioninclusiveZeventsweresimulatedwithMadgraphsoftwareandusedinthisanalysis,asshowninTable 4-7 .TheprimarycontributionofW+jetsasabackgroundprocesstothisstudyisduetoleptonicdecaysoftheWintoanisolatedmuonandaneutrinotogetherwithanon-isolated(possiblyfake)muonproducedintherecoilingjet(s).TheprimarycontributionofZ+jetsisduetodi-leptondecaysoftheZ,togetherwithanon-isolated(possiblyfake)leptonproducedintherecoilingjet(s). 80

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4-6 ).Thenumberoffullysimulatedandreconstructedelectro-weakdi-bosoneventsusedinthisworkmaybefoundinTable 4-7 134 ]. 157 ]andasoftware-basedHigh-LevelTrigger(HLT)system[ 158 ].Forppcollisionsatp 159 ].Thedi-muontrigger(HLT DoubleMu3)withexpectedrate0.79Hzisusedtoselecteventswithasame-chargedi-muonsignature.Thedi-electrontrigger(HLT DoubleEle10 LW OnlyPixelM L1R)withexpectedrate19.96Hzisusedtoselecteventswithsame-chargedi-electronsignature.HLTtriggerforecrosschannelwasnotpresentingeneratedsignalandbackgroundMonte-Carlosamples.Thistrigger(HLT L2Mu5 Photon9)wasrecentlystudiedandintroducedintonewHLTTable[ 160 ].ItsperformancewillbestudiedinfulldetailswithnextversionofMonte-Carlosamples. 81

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161 ]and[ 162 ].Inaddition,formuonspreselectionweappliedafewkinematicandidenticationcuts(seeTable 4-8 )followingcommonlyusedV+jetsgroupbaselinerecommendations[ 163 ].MuonsarerequiredtohavepT5GeV.Thespecicpseudorapidityrangejj2.4ismotivatedbytheacceptanceofmuonsystem.Toreducethecontaminationfromsemi-leptonicheavyavordecayswerequiretheimpactparameterwithrespecttoofinebeamspotofthetrackertofthemuontobelessthan0.02cm.Toenhancethepurityofglobalmuonscomplementaryqualitycutsareapplied.Muonsusedintheanalysishavetosatisfytherequirementofatleast11validhitsintrackert.Thenormalized2oftheglobaltofthemuonisrequiredtobelessthan10(equaltothatusedtoidentifymuonswithGlobalMuonPromptTightidenticationrequirement).Theenergydepositintheelectromagneticcalorimeter(ECAL)withinvetoconeofR=0.07aroundthemuontrackislimitedto4GeVtoensurethemuonisconsistentwithaminimalionizingparticle.Also,theenergydepositinhadroniccalorimeter(HCAL)withinvetoconeofR=0.1aroundthemuontrackislimitedto6GeV. 82

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Muonpreselectioncuts. ReconstructionAlgorithm=GlobalMuon IDType=GlobalMuonPromptTight numberofvalidhitsintrackert11 ECALVetoConeEnergy<4 HCALVetoConeEnergy<6 lossisused.Detailsonelectronsreconstructionandidenticationcanbefoundin[ 164 ]and[ 165 ].KinematiccutsusedforelectronsidenticationandpreselectionaresummarizedinTable 4-9 followingcommonlyusedV+jetsgroupbaselinerecommendations[ 163 ]. Table4-9. Electronpreselectioncuts. ReconstructionAlgorithm=PixelMatchGsfElectron IDType=robustLoose 4-10 followingcommonlyusedV+jetsbaselinecuts. Table4-10. Jetpreselectioncuts. ReconstructionAlgorithm=sisCone5CaloJets HadronicEnergyFraction0.1 83

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4-4 .DuetothesomewhatsoftSUSYleptonspectrum,theleptontransversemomentumisseentobehaverathersimilarlytothebackground(thoughtheleadingleptonpTisperhapsmildlyharderthanthebackgrounds). 84

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Transversemomentumofreconstructedleading(topleft)andnext-to-leading(topright)muonsinsame-chargedi-muonchannelandtransversemomentumofreconstructedleading(bottomleft)andnext-to-leading(bottomright)electronsinsame-chargedi-electronchannelforSUSYLM0(emptyredhistogram)andtt(shadedbluehistogram)samples. Aspartofthereconstructionprocessforleptons,averyimportantvariable,isolation,iscalculated.Thetrackerisolationquantity(IsoTk,0
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4-5 .Note,bothleptonsinsame-chargepairsforSUSYsampleareisolated.Onthecontrary,theleastisolatedleptoninsame-chargepairsforttproductionisexpectedtocomefromb-jetandisnotisolated.ThisisclearlyseeninFigure 4-5 (right). 4-6 (topleft)thatjet 86

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Relativeisolationofreconstructedmostisolated(lefttop)andleastisolated(righttop)muonsinsame-chargedi-muonchannelandrelativeisolationofreconstructedmostisolated(lefttop)andleastisolated(righttop)electronsinsame-chargedi-electronchannelforSUSYLM0(emptyredhistogram)andtt(shadedbluehistogram)samples. multiplicityforSUSYLM0sampleishigherthanforttsample.Dependingonthephasespace(ifany)inSUSYparametersthetransverseenergyofjetscanvaryalthoughquitealargeareaofSUSYparametersyieldshighETjets.Forexample,theSUSYLM0benchmarkpointusedforoptimizationintheanalysishasmoderatelyhighETjetsincomparisontojetsfromttsampleasshowninFigure 4-6 4-7 87

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Numberofjets(topleft)andETofleading(topright),next-to-leading(bottomleft)andnext-to-next-to-leading(bottomright)jetsforSUSYLM0(emptyredhistogram)andtt(shadedbluehistogram)samples. Figure4-7. MissingtransverseenergyforSUSYLM0(emptyredhistogram)andtt(shadedbluehistogram)samples. excludedwhensignalispresent.Differentsignatures(,eeande)wereoptimizedseparately.Ageneticalgorithmtool,GARCON[ 166 ],isusedtosearchamulti-dimensionalspaceofcuts,withtheaimofmaximizingthesignicanceofapotentialdiscovery.TheoptimizationisperformedusingtherobuststatisticalestimateofthesignicanceSdescribedinSec. A 88

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Optimizedselectioncutsforallsame-chargedi-leptonchannels. Transverseenergyofleading(1st)jet: Transverseenergyofnext-to-leading(2nd)jet: Transverseenergyofnext-to-next-to-leading(3rd)jet: Relativeisolationofmostisolated: Relativeisolationofleastisolated: Transverseenergyofleading(1st)jet: Transverseenergyofnext-to-leading(2nd)jet: Transverseenergyofnext-to-next-to-leading(3rd)jet: Relativeisolationof: Relativeisolationofe: Transverseenergyofleading(1st)jet: Transverseenergyofnext-to-leading(2nd)jet: Transverseenergyofnext-to-next-to-leading(3rd)jet: Relativeisolationofmostisolatede: Relativeisolationofleastisolatede: 4-8 thatsignicanceofcutsarestableforbroadregionofcutsonthejettransverseenergy. Figure4-8. Signicancevs.cutonETof3rdjet. 89

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Numberofevents(atLHCenergyp Single Single WZ ZZ tt SUSY (bb) Z LM0 Nocuts 46106 3140 990 41500 51106 470 197 3.2 11 2.8 418 25337 244 MET 10 15 1.0 0.17 0.66 0.074 66 93 140 1stjetET 13 1.0 0.17 0.24 0.045 60 85 137 2ndjetET 6.4 0 0.10 0.10 0 33 47 115 3rdjetET 4.6 0 0.035 0.064 0 26 37 104 4.6 0 0.035 0.051 0 21 26 76 0 0 0 0.025 0 0.48 0.51 20 Di-HLT 0 0 0 0 0.025 0 0.39 0.42 19 Skim 0 0 0 0 0.025 0 0.39 0.42 19 3828 1325 35 30 8.6 1408 97070 791 MET 27 130 7.7 2.5 1.5 0.15 173 342 446 1stjetET 50 4.0 0.91 0.78 0.059 121 195 401 2ndjetET 17 0.67 0.42 0.23 0.020 70 96 309 3rdjetET 10 0 0.17 0.09 0.010 53 67 269 5.5 0 0.10 0.064 0.005 21 27 105 0 0 0 0.013 0 0.26 0.28 22 Skim 0 0 0 0 0.013 0 0.26 0.28 22 2759 3154 36 24 8.0 1137 71767 668 MET 206 261 7.7 5.5 2.4 0.35 268 750 482 1stjetET 86 3.3 2.4 1.04 0.12 188 373 432 2ndjetET 19 1.3 0.31 0.22 0.045 75 124 271 3rdjetET 11 0.67 0.21 0.10 0.035 54 84 230 8.2 0.67 0.17 0.089 0.010 33 42 110 0 0 0 0.013 0.010 0.48 0.51 15 Di-eHLT 0 0 0 0 0.013 0.010 0.44 0.46 14 Skim 0 0 0 0 0.013 0.010 0.44 0.46 14 4.5.1Same-chargeDi-muonChannel 4.5.1.1DataDrivenMethodtoEstimatetheQCDBackgroundTheQCDbackgroundcontributiontothesame-chargedi-leptonsignatureisexpectedtobereducedtozerobyimposingbothatightisolationrequirementontheleptonsandahighcutontheMET,aswellasrequiringtheexistenceofathirdhighETjetintheevent.Nonetheless,duetothelargeQCDmulti-jetcross-sectionand 90

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167 168 ].Themethodreliesontheexpectedfactorizationoftheisolationcutsfromthehadroniccutsattheanalysislevel(i.e.,thecutsareuncorrelated).Inorderforthemethodtowork,theisolationandhadroniccutshavetobedesignedsuchthatQCDisexpectedtodominatetheeventyieldsbeforeandaftereachoneofthemisappliedirrespectiveoftheother.Ifthethisistrue,thentheresultingcutefcienciesderivedinthedatacanbetakentobetheQCDcutefciencies.TheproductoftheseefcienciesshouldprovideanupperboundonthetotalQCDyieldafterallcutsareapplied.Onlyanupperboundcanbeobtainedduetothesmall,butnon-negligible,contributionsfromotherSMbackgrounds(e.g.tt)orsignal.ThismethodhasbeentestedinMonteCarloforthecasewithsignal(LM0)andwithoutsignal.TheresultsindicatethatanupperboundontheQCDcontributioncanbeplacedat0.120.01eventsforthecasewithoutsignal,assuminga100pb1scenario.Thecompletedescriptionofthismethodcanbefoundelsewhere[ 167 168 ]andhassofarbeendemonstratedtobefeasibleonlyforthedi-muonnalstate.Similarstudiesfortheelectron-muonanddi-electronnalstatewillbecompletedinthenearfuture. 91

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4-9 .Forcomparisonthemuonisolationfromttisalsoshownandtheyareinreasonableagreement. Figure4-9. TheisolationtemplateformuonsfromQCD(blueline).Theisolationdistributionformuonsfromttisshownforcomparison(redline). Thecompletedescriptionofthismethodcanbefoundelsewhere[ 169 170 ]andhassofarbeendemonstratedtobefeasibleonlyforthedi-muonnalstate. 171 ]. 4-13 listssystematicuncertaintiesforsignal.Roughestimatesofthelevelsoftheuncertaintiesweretakenfrom[ 104 ].Forcompletenessuncertaintyonmissingtransverseenergywasaddedtothelist.Conservativelyweareusingthesame 92

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Table4-13. SummaryofsystematicuncertaintiesforSUSYsignalincludedintheanalysis. total 27.5% Inthenextupdateoftheanalysisthesystematicuncertaintieswillbebetterevaluated.ToreduceimpactofsystematicuncertaintiesonthenalresultsthedatadrivenmethodstoestimatebackgroundswillbeusedasdescribedinSec. 4.5.1.2 andSec. 4.5.1.1 4-14 ).Figure 4-10 (top)showsthe5reachcontoursofallsignaturesofthisanalysis(withandwithout30%systematicuncertainties)inthemSUGRAm0m1=2plane,assumingL=100pb1forp 4-10 (bottom)showstheCL=95%exclusionlimitsofallsignaturesofthisanalysis(withandwithout30%systematicuncertainties)inthemSUGRAm0m1=2plane,assumingL=100pb1forp 93

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Top:theCMS5reachcontoursatp 94

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4-14 )numberofeventsatp Table4-14. Numberofevents(atLHCenergyp AllCuts QCD Single Single WZ ZZ tt SUSY (bb) Z LM0 0 0 0 0.015 0 0.16 0.17 6.6 0 0 0 0.007 0 0.09 0.09 7.6 0 0 0 0.007 0.006 0.14 0.15 4.9 Figure 4-11 (top)showsthe5reachcontoursofallsignaturesofthisanalysis(withandwithoutsystematicuncertainties)inthemSUGRAm0m1=2plane,assumingL=100pb1forp 4-11 (bottom)showstheCL=95%exclusionlimitsofallsignaturesofthisanalysis(withandwithoutsystematicuncertainties)inthemSUGRAm0m1=2plane,assumingL=100pb1forp 172 ]takingintoaccountthedifferenceinappliedcutsandusageofk-factorsforSUSYsamplesintheanalysis. 95

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97

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173 ].InlaterCMSstudies[ 174 ]withcosmicraymuonsusingallCSCsduringtheCosmicRunatFourTesla(CRAFT)in2008theresultsofthisworkwereusedasabenchmark. 157 ].TheyarealsoanecessaryconditionforreadingoutCSCdata,i.e.,CSCdataarepresentintheDataAcquisitionSystem(DAQ) 98

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5-1 ).DesiredALCTpatternscanbeprogrammedindividuallywithintheboundaryofthisenvelope.Weusedthedefaultpatternsfullyspanningtheenvelope,whichprovidesthewidestacceptance.ThethirdCSClayeriscalledthekey-layer:foreachwiregroupinthekey-layer,thermwareseeksanodehitsthatliewithinALCTpatternskeyedtothatwiregroup.Forapatterntobevalid,hitsfromatleast4planesarerequiredtobepresentinthepatternincludingthekey-layer.OutofallALCTsthatmaybepresentinachamber,theelectronicsreportsonlythe2best-qualityonespereachbunchcrossing,ALCT0andALCT1.ThisisadequatefortheexpectedchambertrackoccupancyatthenominalLHCluminosity.Thepatternqualitydependsonthenumberofplanespresentinapatternanditsycoordinate.Thereportedpatternshavetagsidentifyingthekeywiregroupstheyareassociatedwith(markedasinFigure 5-1 ).Similarly,CathodeLocalChargedTrackpatterns(CLCT)aresearchedforamongcomparatorhalf-striphits.UnlikethecaseofALCTs,thereare7CLCTpatterns.ThesepatternsareshowninFigure 5-2 :thestraight-throughpatterncorrespondstohighpTmuons(pT>30GeV),whilemoreinclinedpatternswoulddetectsoftermuons.Forapatterntobevalid,hitsfromatleast4planesarerequiredtobepresentinthepattern.Inaddition,4adjacenthalf-stripcomparatorbitsarecombinedtoform1di-stripbit.Theelectronicsalsochecksforpresenceofpatternsmadeofdi-strips,whichallowsonetochooseandtriggeronhighlyinclined,i.e.,lowpT,muons.TheCLCT-searchingrmwarereportsthe2best-qualityCLCTsperbunchcrossing,CLCT0andCLCT1.The 99

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Figure5-1. WiregroupsbitpatternusedforconstructingALCTs.Thekeywiregroupismarkedwithacross. Figure5-2. ComparatorbitpatternsusedforconstructingCLCTs.Thekeyhalf/di-stripismarkedwithacross.Thestraight-throughpattern(left)correspondstohighpTmuons,whilemoreinclinedpatternswoulddetectsoftermuons. 139 ]exercise,asubstantialpartoftheCMSdetectoroperatedasonesystem.TheMTCCexercisetookplaceaboveground(i.e.notintheexperimentalhallcavern).TheEndcapMuonSystemwasrepresentedbya60sectoroftheME+endcap.Figure 5-3 showsthelayoutofchambersthatwerepresentintheMTCCintheglobalCMScoordinatesystem.Atotalof36chamberswereoperationalduringthesetests.Thedatausedinthisanalysisweretakenwiththemagneticeldturnedoff. 100

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157 175 ],which,bynecessity,werealwayslimitedtoverysmallchamberareas,typicallyoftheorderoforlessthan1010cm2. Figure5-3. CSCsthattookdataduringtheMTCC.HighlightedchamberswereoperationalduringtheMTCC.Left:Sideview.ThesolidboxesschematicallyshowthelocationsofALCTsthatwereactuallyfoundforamuonin3chambers.TheopenboxindicatesthepredictedALCTpositionintheME+2stationforthismuonbasedonthemeasurementsinME+1andME+3.Right:TransverseviewoftheME+2station. AnexampleoftypicaleventconsideredintheanalysisisshowninFigure 5-4 .VisualizationofthiseventwasperformedbytheInteractiveGraphicsforUserAnalysis(IGUANA)system[ 176 ].Wireandstriphitsin3chambers(ME+1=2=30,ME+2=2=30,andME+3=2=30)arerepresented. 101

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3-10 ).Sinceweusedrunstakenwiththemagneticeldturnedoff,themuontrackwasassumedtobeastraightlinegoingthroughthe2space-pointsassignedtotheME+1andME+3tracksegments.TheALCT-andCLCT-ndingelectronicsaredesignedtohavehighefciencyformuonsoriginatingfromtheInteractionPoint(IP).WeselectedeventswherethepredictedtrackdirectionwouldresembleIP-likemuons.Thiswasachievedbyselectingeventsinwhichthelocalpolarangleofthetrack(seeFigure 5-3 )predictedfromtracksegmentsintheME+1andME+3stationswaswithin0rad.Inaddition,then-numberofthechamberswithtracksegmentsintheME+1andME+3stationshadtobethesame(e.g.,ME+1=3=27andME+3=2=27).NotethatthequotesinIP-likeareessential:wedidnotactuallyrequireselectedmuonstopointbackexactlytotheIP;ifwehad,wewouldhavehadaverysmalleventsampletoworkwith.EventsinwhichthepredictedtrackswouldmissthegeometricalareaoftheME+2chambers(limitedinther-planebyupperandlowerdistancesfromthebeamlineaswellasminimumandmaximumazimuthalangles)wereexcludedfromtheanalysis.Afterthesecuts,weendedupwith759tracksgoingthroughME+2=1chambersand14100tracksgoingthroughME+2=2chambers.TherearefewertracksthroughtheME+2=1chambersbecausetheyaresmallerinsizeand,moreimportantly,requiremore 102

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5-5 .Thechamberwireplanesarenotcontiguousfromthenarrowendtothewideend.Thereare2or4breaksof25mmwidthatapproximatelyevery60cm,whichcreate3or5independenthighvoltagesegmentsperplane.Thesebreakpointsarealsousedtointroducepanelsupports,withoutwhichthepanelswouldbulgeorcaveinandstablechamberoperationwouldnotbepossible.Thesebreakpoints,indicatedbydashedlinesinFigure 5-5 ,resultindeadzones.Thesedeadzoneslineuphorizontallyandmostlyeffecttrackswithsmaller-angle. 5-1 .Theaverageefciency,withoutanyducialcuts,wasaround97%%.Figure 5-6 showsonlythosepredictedtrackpositionsintheME+2=1andME+2=2chamberswhenno2d-LCTwerereported.Onecanclearlyseetheclusteringoccurringaroundthechambergeometricaldeadzones.Theefciencydependsonthelocalpolarangleofamuon'strackasshowninFigure 5-7 (left).Onecanseethattheefciencydecreasesforsmallerangletracks.TolooseanLCT,oneneedstoloosehitsin3ormoreplanes.Astraightforwardgeometricanalysisofhowtrackwithdifferent-anglescrossthedeadareasbetweenhighvoltagesegmentsresultsinthecurvealsoshowninthegure.Althoughthecurve 103

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ScreenshotoftheinteractiveIGUANA-basedeventdisplay,showingCSCswithstripandwirehitsfromacosmicmuonthatpassedthrough3stationsoftheEMUsystem. Figure5-5. PredictedpositionsofmuonhitsinME+2=1(left)andME+2=2(right)chambers. 104

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Figure5-6. PredictedpositionsofmuonhitsinME+2=1(left)andME+2=2(right)chamberswhenLCTsinME+2arelost. Figure5-7. EfciencytoreportamuonLCTasafunctionoftrackanglewithoutducialcuts(left)andafterexcludingsemi-deadzones(right)inME+2chambers.Thepredictedefciencycurvebasedongeometricanalysisisshownasthesolidline. TomeasurethetrueCSCefciency,i.e.,excludinggeometricaldeadzones,weappliedducialcutsonthepredictedtrackstoeliminatethosethatwouldcrossdeadzones.ThechamberareaswithfullacceptanceareshowninFigure 5-6 asdashedpolygons.Thebordersfortheseareasweredenedsothattrackswithourselectionofalloweddirectionswouldnevermiss3ormoreplanesduetodeadzonesorchamberedges.Theseareaswerereducedfurtherby1.5cmtoaccountfortheniteprecisions,dxanddy,withwhichwecouldpredictmuontrackpositionsintheME+2chambers.Thesecorrectionscorrespondedto3dxand3dy(seeAppendix 105

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5-2 .TheefciencydependenceofatrackangleafterapplyingtheducialcutsisshowninFigure 5-7 (right).Itisgreaterthan99%forallangles.Toconrmthatwhatwemeasuredistheefciencytondmuon-associated2d-LCTs(ratherthanjustnoise),weplottedthedifferencesbetweenthepredictedmuontrackxandypositionsandtheactual2d-LCT0sreportedbytheME+2chambers(Figure 5-8 ).Thepositionsofthe2d-LCT0sintheME+2-chambersweredenedbythecentersoftheALCT0keywiregroupsandCLCT0keyhalf-strips. Figure5-8. MuonhitsresidualsinME+2=1(left)andME+2=2(right)chambers. TheLCTsfoundintheME+2chambersarewithin0.5cmaroundthepredictedpositions,whichisconsistentwiththeexpectedmultiplescatteringofcosmicraymuonsandthewidthsofthestripsandwiregroups.Forfurtherdiscussion,seeAppendix.NotethattheME+2=2chambersaredistinguishedbyalargedy2.1cm.Thisisbecausethesechambershavemuchwiderwiregroups:w=51mmvs.19mmfor 106

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Table5-1. Efcienciestodetectmuon2d-LCTsbyME+2chamberswithoutducialcuts.Theerrorsarestatistical. Numberof Numberofeventswith Efciency selectedevents no2d-LCTreported toreport2d-LCT ME+2=1 759 22 97.10.6% ME+2=2 14100 267 98.10.1% Table5-2. EfcienciestodetectmuonLCTinME+2chambersafterexcludingsemi-deadzones. Numberof Numberofeventswith Efciency triggeredevents undetectedmuons toreportLCT ME+2=1 532 1 99.8+0.120.33% ME+2=2 9990 7 99.93+0.0280.033% DuringtheCosmicRunatFourTesla(CRAFT)in2008theresultsofthisworkwereusedasabenchmarktomeasureefciencyofallCMSCSCs[ 174 ]. 107

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(A) ThenumberofpredictedbackgroundeventsNbmaybefactorkdifferentfromtheunknowntruebackgroundnb,duetosomesystematicuncertainty.BecausethepredictionforNbisoftenclosetozero,thenumberoftruebackgroundeventsnbisassumedtohavealog-normaldistributionaboutthepredictionNb: 2lnnblnNb (A) Hence,foratotalnumberofbackgroundeventsNb,predictedwithasystematicuncertaintyincludedasinEq. A ,theprobabilitydensitytoobserveNeventsis (A) Theincompatibilityofthesignalplusbackground(Ns+Nb)withthebackground-onlyhypothesis(Nb)isthenestimatedbyconvertingtheone-sidedprobabilitytail: (A) toaGaussian-equivalentsignicanceS,bysolvingtheequation: 1 2ZS01 2dx=P(Ns,Nb). (A) BecausetheprobabilityP(Ns,Nb)iscalculatedvianumericalintegrationbeforebeingconvertedtoasignicance,theestimationforSislimitedbythenumericalprecision 108

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109

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R+10Rp(n0jb0kx+rs0kx)g(x)dxdr,whereg(x)isthenormalprobabilitydistributionfunction.Exclusionlimitisthenobservedfromequationonr:Z+1rL(r)dr=,where,forexample,=0.05for95%condencelevel. 110

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C-1 FigureC-1. MassspectrumofSUSYLM0benchmarksample[ 177 ]. InputlefortheLM0mSUGRAbenchmarksampleinLesHouchesformatisshownbelow.

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TableD-1. Numberofevents(normalizedtoanintegratedluminosityof100pb1)forSUSYLM0FullSimandFastSimsamplesaftersequentiallyapplyingthenalsetofcutsforallsame-chargedi-leptonchannels. 10TeVFastSim LM0(A0=400) LM0(A0=400) LM0(A0=0) i (%) (%) (%) (%) (%) Nocuts 0 16601 100 16577 100 14550 100 244 1.5 1.5 243 1.5 1.5 110 0.76 0.8 MET 2 140 0.84 57 140 0.85 58 77 0.53 69 1stjetET 137 0.83 98 137 0.83 98 75 0.52 98 2ndjetET 115 0.69 84 114 0.69 83 63 0.43 83 3rdjetET 104 0.63 90 101 0.61 89 54 0.37 87 76 0.46 73 75 0.45 75 37 0.26 69 20 0.12 27 19 0.11 25 7 0.049 19 Di-HLT 8 19 0.11 95 18 0.11 95 7 0.047 96 Skim 9 19 0.11 100 18 0.11 100 7 0.047 100 791 4.8 4.8 657 4.0 4.0 355 2.4 2.4 MET 2 446 2.7 56 373 2.3 57 234 1.6 66 1stjetET 401 2.4 90 334 2.0 89 210 1.4 90 2ndjetET 309 1.9 77 252 1.5 75 154 1.1 73 3rdjetET 269 1.6 87 212 1.3 84 128 0.88 83 105 0.63 39 81 0.49 38 43 0.30 34 22 0.13 21 21 0.13 26 10 0.068 23 Skim 8 22 0.13 100 21 0.13 100 10 0.068 100 668 4.0 4.0 445 2.7 2.7 262 1.8 1.8 MET 2 482 2.9 72 319 1.9 72 209 1.4 80 1stjetET 432 2.6 90 282 1.7 88 183 1.3 88 2ndjetET 271 1.6 63 177 1.1 63 110 0.76 60 3rdjetET 230 1.4 85 145 0.88 82 88 0.61 80 110 0.66 48 85 0.51 59 45 0.31 50 15 0.088 13 15 0.089 17 6 0.042 14 Di-eHLT 8 14 0.086 98 15 0.088 99 6 0.041 98 Skim 9 14 0.086 100 15 0.088 100 6 0.041 100

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Transversemomentumofreconstructedleading(topleft)andnext-to-leading(topright)muonsinsame-chargedi-muonchannelandtransversemomentumofreconstructedleading(bottomleft)andnext-to-leading(bottomright)electronsinsame-chargedi-electronchannelforSUSYLM0FullSim(emptyredhistogram)andSUSYLM0FastSim(shadedgreenhistogram)samples. 124

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Relativeisolationofreconstructedmostisolated(lefttop)andleastisolated(righttop)muonsinsame-chargedi-muonchannelandrelativeisolationofreconstructedmostisolated(lefttop)andleastisolated(righttop)electronsinsame-chargedi-electronchannelforSUSYLM0(emptyredhistogram)andtt(shadedgreenhistogram)samples. FigureD-3. Numberofjets(topleft)andETofleading(topright),next-to-leading(bottomleft)andnext-to-next-to-leading(bottomright)jetsforSUSYLM0(emptyredhistogram)andtt(shadedgreenhistogram)samples. 125

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MissingtransverseenergyforSUSYLM0(emptyredhistogram)andtt(shadedgreenhistogram)samples. 126

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5-1 .Sincemuonswithlarger-anglesarepreferred1,thepatternwasmovedalongachamberstartingfromitswidesideinward,onekeywiregroupperstep.If6layerswithanodehitswerepresentinthepatternatsomestep,thenananodesegmentwasreportedandallhitsinsidethispatternweredeleted.Uponreachingthenarrowendofthechamber,theprocedurewasrepeatedagainwitharequirementof5and,then,4layerswithhitsinthepattern.Anodesegmentswerenumberedsequentially,AS0,AS1,etc.Thefoundanodesegmentswereassigned(yAS,zAS)-coordinatesbytakingthecenterofgravity(COG)ofhitsassociatedwiththem.Iftherewasmorethan1hitperplaneinapattern,thehitweightswerereducedsothatthetotalweightperplanewasalways1.Inaddition,alineartwasusedtoevaluatethesegmentslopedy=dz.Forawiregroupwidthw,theexpectederror(RMS)ontheyAScoordinatewouldbew=p E-1 (theywereobtainedfromthemostrecent 127

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FigureE-1. Comparatorbitpatternsusedforconstructingcathodesegments.Thekeyhalf-stripismarkedwithacross. Anodeandcathodesegmentswerethencombinedtomakeacomplete2-dimensionalTrackSegment(TS).WhenevermultipleASsand/orCSswerefound,weusedallpossiblecombinatorialpairingstomakefull2d-TSs.IfzCSandzASweredifferent,thetracksegmentzcoordinatezTSwastakenaszTS=0.5(zCS+zAS)and(TS,yTS)-coordinateswererecalculatedforthenewzTS-locationusingthed=dzanddy=dzslopes.Toevaluatetheperformanceofthealgorithm,weappliedittoallthechambersinall3stations.First,wefoundthatthealgorithmdidndatleastonetracksegmentinallchamberswith2d-LCTsreportedbyhardware(totalof10522events).Therefore,theefciencyofndingtracksegmentscanbeestimatedtobe>99.97%atthe95%CLforchamberswithhardware-foundLCTs.NotethatchambersinwhichhardwaredidnotndanLCTwouldnotbeavailableforfurtheranalysis(High-Leveltriggerorofine). 128

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E-2 (ME+2=1chambers)andFigure E-3 (ME+2=2chambers).Fortheseplots,ifthereweremultipleTSsreconstructedinthesechambers,weusedthebesttracksegment,TS0,evenifitwasnottheclosesttothepredictedtrackposition.OnecanseethatthedxanddydistributionsforME+2=1andthedxdistributionforME+2=2havecorewidths3.5mm.ThedydistributionforME+2=2hasacorewidth6mm.Also,onecanclearlyseethatresidualsarenotcenteredaroundzero;thisisduetotheEndcapdisks'misalignmentduringtheMTCC,whichwasconrmedbygeodesicsurvey. FigureE-2. MuonhitresidualsinME+2=1chambersafteranalgorithmsearchfortracksegmentsandapplyingtheCOGtechniquetondthemuontracksegmentcoordinates. Toshowthattheobtainedresidualsareconsistentwithmultiplescatteringofmuons,weperformedthefollowingcalculations.Amuonwithanaverageinclinationof0.4radwithrespecttothehorizonwouldloseapproximately9GeVonitswaythroughthewholeCMSdetectorbeforehittingtheEndcapMuonsystem(seeorientationoftheCSCchambersusedintheMTCC,Figure 5-3 ).AmuonthathitstheME+1=1chambershastohaveanenergyofatleast2GeVtopassthrough2steeldiskstoreachtheME+3station.TheapproximatecosmicraymuonspectrumdN=dEE2.7[ 178 ]isshownin 129

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MuonhitresidualsinME+2=2chambersafteranalgorithmsearchfortracksegmentsandapplyingtheCOGtechniquetondthemuontracksegmentcoordinates. Figure E-4 (left).TheadditionalaxisonthisplotshowsbyhowmuchthemuonenergyspectrumshiftsafterpassingthroughCMS,justbeforehittingtheME+1chambers.ThelledareashowsonlytheportionofthespectrumcorrespondingtomuonsthatcanreachtheME+3chambers.Then,foramuonofagivenenergy,wecalculatedtheexpected,multiplescatteringinduced,dN=dx(E)-spreadbetweenthemuoncoordinatemeasuredintheME+2=2chambersandthecoordinatepredictedfrommeasurementsintherstandthirdstations.Afterthat,the2distributions,dN=dx(E)anddN=dE,wereconvoluted.TheresultforME+2=2isshowninFigure E-4 (right).Itisclearthattheobservedresidualsareconsistentwithoursimplemodel.Thesamelevelofagreementwasobservedforotherchambersandprojections.Fromtheseplots,wecanconcludethatmultiplescatteringisthedominantcontributiontotheresidualsofthecathodesegmentmeasurements.TheanodesegmentmeasurementprecisioninME+2=1chambersisalsodominatedbymultiplescattering.ThelargeME+2=2chambershavewidewiregroups,whichlimitstheaccuracyofcoordinatemeasurementsto6mm.Next,welookedatthenumberandqualityofthefoundsegments(thealgorithmallowsustondasmanysegmentsasthereareinachamber).Distributionsofthenumbersoffoundanode,cathode,andcombined2-dimensionaltracksegments(AS,CS,andTS)inME+2chambersareshowninFigure E-5 .Theseeminglyirregular 130

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Cosmicraymuonspectrum(left).Muonhitdx-residualsinME+2=2chambers(right),wherethehistogramcorrespondstothemeasureddataandthelinegivesourexpectationsforthemultiplescatteringcontribution. patternoftherightmostplotisdrivenbycombinatorics,notbystatistics.InaperfectworldwheneachtrackgoingthroughachamberwouldgiveexactlyoneALCTandoneCLCT,theonlybinsthatwouldbepopulatedare11=1(onetrack),22=4(twotracks),33=9(threetracks),etc.Overlappingtracksinoneprojectiongiverisetoadditinalentriesinbins2(21)=2,3(31)=6,etc.Occasionalspurious1d-LCTswouldgivethesamepatterns:1(1+1)=2,2(2+1)=6.Othercombinations,like13=3,15=5,17=7,areveryrare.Thisisexactlythepatternweobserve. FigureE-5. Distributionsofnumbersofanode(left),cathode(center),andcombined2-dtracksegmentsfoundintheME+2chambers. Table E-1 showsthenumbersofeventswithdifferentcombinationsoffoundsegments.About95%oftheeventsweresimpleastheyhadonly1ASand1CS(and,therefore,only12d-TS).Alleventswithmultiplesegmentswerevisuallyscanned 131

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E-6 showsthedistributionofthepatternqualitiesfortheclosestandallothersegments. FigureE-6. Quality(numberoflayerswithhits)distributionsofprimary(upperplots)andsecondary(lowerplots)segmentsinME+2chambers.Theprimarysegmentistheoneclosesttothepredictedmuontrackposition;allothersaresecondary. Finally,webenchmarkedtheCPUperformanceofthealgorithmusingMTCCdata.Theaveragetimerequiredtoreconstructallsegmentsinachamberwithatleast1 132

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TableE-1. Numberofevents(withfractioninbrackets)fordifferentnumbersofanode(AS)andcathode(CS)segmentsintheME+2chambers. AS 1 2 3ormore 1 10011(95.1%) 113(1.1%) 6(0.06%) CS 2 160(1.5%) 171(1.6%) 13(0.12%) 3ormore 5(0.05%) 17(0.16%) 26(0.25%)

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YuriyPakhotinwasbornonMay8th,1977,inthecityofBerdskwhichislocatedinNovosibirskregionofRussia.InthesameyearhisfamilymovedtothecityofTselinograd(nowAstana)inKazakhstan.Aftergraduationwithhonorsfromhighschoolin1994hemovedbacktoSiberiaandbeganundergraduatestudyattheNovosibirskStateUniversity(Novosibirsk,Russia).UndersupervisionofProf.GuramKezerashvilihewrotebachelor'sthesisPositionMonitorfortheHighEnergyGamma-quantaBeamandgraduatedwithhonorin1998.ThenheenteredtheMasterprograminHighEnergyPhysicsatthesameuniversitythathenishedwithhonorin2000.Thetitleofhismaster'sthesiswasDevelopmentoftheInteractionSystemofLaserRadiationandPositronBeamatVEPP-4MCollider.Forthenext3yearsheworkedattheBudkerInstituteforNuclearPhysics(Novosibirsk,Russia)asaresearchassistantandattheNovosibirskStateUniversityasateachingassistant.In2003heenteredtheDoctorateprograminHighEnergyPhysicsattheUniversityofFlorida(Gainesville,Florida).UndersupervisionofProf.GuenakhMitselmakherandco-supervisionofProf.AndreyKorytovhewrotedoctor'sthesisCompactMuonSolenoidExperimentDiscoveryPotentialforSupersymmetryinSame-chargeDi-leptonEvents.InAugust2010hegraduatedwithDoctorofPhilosophydegreefromtheUniversityofFlorida. 147