b-Quark Physics with the LEP Collider: The Development of Experimental Techniques for b-Quark Studies from Z^0-Decay

ISBN-13: 9783642052781 / Angielski / Twarda / 2010 / 200 str.

Gary John Barker

Opis

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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Spis treści

b-physics at LEP.- Silicon Vertex Detectors and Particle Identification.- Experience in Reconstructing Z0 ? b?b Events.- Tagging Z0 ? b?b Events.- Tagging b-quark Charge.- Double-Hemisphere Tagging.- Optimal b-Flavour and b-Hadron Reconstruction.- Conclusion and Next Steps.

Blurb

The book reviews the unexpected impact that the LEP experiments have had on the subject of b-quark physics. The emphasis is firmly on telling the story from an experimental viewpoint. Aspects of the detectors that were essential for the reconstruction of b-hadrons are highlighted, especially the role played by silicon strip detectors and particle identification methods. The importance of solving practical issues such as detector alignment and track reconstruction to fully realize the reconstruction potential of the detectors is demonstrated along with various examples of potential problems when these aspects are not well controlled. Barker details new ideas and analysis techniques that evolved during the years of LEP running so that the information is useful to new researchers or those putting together plans for future b-physics experiments. Highlights of the final b-physics results from the LEP collaborations are reviewed in the context of results from other experiments around the world and with respect to what we learn about the Standard Model of Particle Physics.