b-Quark Physics with the LEP Collider

Theb-physicsresultsfromtheLEPdatasetsexceededallexpectationsinboththe range of topics covered and the precision of measurements that were eventually possible. Thesuccesswasduetoseveralfactorssuchastherapiddevelopmentof silicon-strip vertex detectors, advances in the theoretical description of b-hadrons and not least because of the inventiveness, skill and determination of the expe- mentersperformingthedataanalysis. Inordertoutilisefullytheprecisionofthe newvertexdetectors,carefulcommissioningandeventreconstructionwasneeded. Thistogetherwithnewmethodsandtechniquesofdataanalysis,particularlyinthe areaofinclusiveb-hadronreconstruction,werethekeytoawholehostofmeasu- mentsthatspannedtheentire?eldofb-physics. Theaimofthisbookisnottogiveanotherreviewofb-physicsresults. Instead the focus is on reviewing the main experimental methods that evolved (hardware andsoftware)andthelessonslearntfromsomebodywhowasinvolved?rst-handin theirdevelopmentanduse. Thehopeisthatthisworkwillbothstandasarecordof whatwasachievedwiththeLEPdata,andalsoasareferencesourceofb-physics analysisideasforexperimentersembarkingonprojectsinthefuturee. g. attheLHC oralinearcollider. ResultsfromallfouroftheLEPexperimentsarereportedbutsomebiastowards DELPHIisinevitable,especiallytoillustrategeneralpoints,sinceIamacolla- rationmemberandhaveeasieraccesstomaterial. Iwishtothankmyfriendsand colleaguesoftheDELPHIcollaborationformakingtheprojectsuchasuccess. InadditionIwishtogivespecialthanksto:Prof. Dr. MichaelFeindtwhowasthe instigatorofinclusiveanalysismethodsforb-physicswiththeLEPdata;Prof. Dr ThomasMullerforgivingmetheopportunityandencouragementtowritethisar- cle;Dr. RichardHawkings(OPAL)andDr. ChristianWeiser(DELPHI)forallowing meaccesstosomeunpublishedresultsandforusefuldiscussions. FinallyIwould liketothankthepeopleatSpringer,especiallyUteHeuserforherprofessionalh- dlingoftheprojectandpatiencewithmyregularfailuretomeetdeadlines. UniversityofWarwick,UK GaryJ. Barker September2009 vii Contents 1 b-physics at LEP ...1 1. 1 Introduction ...1 1. 2 TheLEPMachineandExperiments ...3 1. 3 b-PhysicsOverview...4 1. 3. 1 b-QuarkProduction...7 b 1. 3. 2 Forward-BackwardAsymmetry A ...7 FB 1. 3. 3 R ...9 b 1. 3. 4 HeavyQuarkSymmetry...10 1. 3. 5 b-QuarkFragmentation...10 1. 3. 6 b-HadronSpectroscopy ...12 1. 3. 7 b-HadronProductionFractions...13 1. 3. 8 Weakb-QuarkDecay...1 3 1. 4 Combiningb-PhysicsResults...18 1. 4. 1 AveragingofElectroweakHeavyFlavourQuantities...19 1. 4. 2 AveragingofNon-electroweakHeavyFlavourQuantities...20 References ...20 2 Silicon Vertex Detectors and Particle Identi?cation ...23 2. 1 Silicon-StripVertexDetectors ...23 2. 2 ParticleIdenti?cation...29 2. 2. 1 Speci?cIonisationEnergyLoss,dE/dx ...30 ? 2. 2. 2 CerenkovRingImaging ...31 2. 2. 3 OverallDetectorPerformance ...32 References ...34 0 ~ 3 Experience in Reconstructing Z ? bb Events...37 3. 1 ImpactParameterandDecayLength ...37 3. 1. 1 ClusterFinding ...40 3. 1. 2 TrackFittingandPatternRecognition ...41 3. 1. 3 VertexDetectorAlignment...43 3. 1. 4 SingleHitUncertainties...49 3. 1. 5 ResolutionTuning ...