b-Quark Physics with the LEP Collider

Theb-physicsresultsfromtheLEPdatasetsexceededallexpectationsinboththe range of topics covered and the precision of measurements that were eventually possible.… Lue lisää 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 . ..