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Observation of Orbitally Excited B Mesons with the DELPHI Detector

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Observation of Orbitally Excited B Mesons with the DELPHI Detector IEKPKA Observation of Orbitally Excited B Mesons with the DELPHI Detector at LEP Christof J Kreuter Zur Erlangung des akademischen Grades eines DOKTORS DER NATURWISSENSCHAFTEN von der Fakultat fur Physik der Universitat TH Karlsruhe genehmigte DISSERTATION Tag der mundlic hen Prufung Referent Prof Dr W de Boer Korreferent Prof Dr Th Mul ler Diese Arb eit wurde gefordert vom Land BadenWurttem berg Abstract First exp erimental evidence for the existence of orbitally excited B meson states is ob tained byinvestigating the B and B Qvalue distributions Q mB mB m using Z decaydatataken with the DELPHI detector at LEP The mean Qvalue of the decays B B is measured to b e stat syst MeVc The Gaussian width of the signal is stat syst MeVc The observed shap e is consistent with the pro duction of several broad states and several narrow states as predicted by the quark mo del and HQET and whichhave b een observed in the D meson sector The mean mass for B mesons is extracted to b e stat syst MeVc and the pro duction rate of stat syst In addition the B mesons p er bjet is measured to b e helicity distribution of B mesons is investigated A search is p erformed for orbitally excited strange B meson states in the decay B s B K Atwop eak structure in the B KQvalue distribution Q mB mB s mK is observed which can b e describ ed by the pro duction of the predicted narrow B s states B and B The mass of the B state is determined to b e stat syst s s s while the mass of the B state is determined to b e stat syst The pro duc s tion rates p er bjet are stat syst for the B state and s stat syst for the B state s First exp erimental evidence for the b eautybaryons and is presented in an anal b b ysis of the Qvalue distribution Q m m m Atwop eak struc b b b ture is observed on top of a at background which can b e describ ed by the pro duction of is determined to b e baryons The mean Qvalue of the decays and b b b b is determined to b e stat syst MeVc and that of the decays b b stat syst MeVc The pro duction rate of and baryons p er bjet is b b measured to b e stat syst The pro duction ratio b b b is found to b e stat syst The helicity angle distribution of the signal identied as suggests a suppression of the helicity states b Contents Intro duction The Theoretical Background The Static Quark Mo del Mesons q q states Baryons qqq states Quantum Chromo dynamics The QCD Lagrangian The Running Coupling Constant s Symmetries in QCD Heavy Quark Symmetry Potential Mo dels From Quarks to Hadrons The Electroweak Phase The Perturbative Phase The Fragmentation Phase Hadron Decays B Meson Sp ectroscopy Ground State B Mesons B Mesons with Orbital Excitation Motivations from the D Meson Sector Predictions for Orbitally Excited B Mesons Flavour Tagging and CPViolation b Baryon Sp ectroscopy Heavy Baryons PresentKnowledge ab out b Baryons Baryons Predictions for and b b Summary of the Chapter The Exp eriment The LEP Collider The DELPHI Detector The Tracking System The Calorimeters Particle Identication Devices The DELPHI Online System The SlowControl System The Trigger The Data Aquisition System The DELPHI Oine Analysis Chain The DELANA Package The SDST Creation The DELPHI Event Display The Detector Simulation Summary of the Chapter Analysis Tools Hadronic Event Selection Tagging of bb Events Inclusive B Meson Reconstruction B DecayVertex Reconstruction Hadron Identication V Reconstruction Summary of the Chapter The Analysis Observation of Orbitally Excited B Mesons B B Exp erimental Pro cedure and Results Interpretation and Comparison with Predictions B Helicity Analysis B Charge Analysis B Fragmentation Comparison with other Exp eriments Search for Orbitally Excited Strange B Mesons B B K s Exp erimental Pro cedure and Results Interpretation and Comparison with Predictions Comparison with other Exp eriments Search for and Baryons b b b b Exp erimental Pro cedure and Results Interpretation and Comparison with Predictions Helicity Analysis b Summary References Memb ers of the DELPHI Collab oration Acknowledgements List of Figures SU Meson Multiplet SU Baryon Multiplet Feynman Graphs of the Fundamental Pro cesses of QCD Onelo op Contributions to the Vacuum Polarisation From Quarks to Hadrons Hadron Pro duction in e e Annihilation Schematical View of the String Fragmentation Algorithm Longitudinal Fragmentation Function Particle Decays in the Sp ectator Mo del Pro duction of Vector and Pseudoscalar Mesons at LEP The Coupling Schemes of Symmetric and HeavyLight Mesons Pro duction and Decay Prop erties of Orbitally Excited B Mesons Flavour Change in B Decays Decay Prop erties of Orbitally Excited B Mesons Orbital Angular Momenta for a Light Diquark System Lo cal Area Map of the LEP Collider Schematic View of the LEP Injection System Integrated LuminosityAveraged over the LEP Exp eriments Schematic View of the DELPHI Detector Schematic View of the DELPHI Detector along the Beam Pip e Schematic Layout of the DELPHI Microvertex Detector Hadronic Z Event in the DELPHI Vertex Detector Layer Structure of the High density Pro jection Chamb er HPC The Ring Imaging Cherenkov Detector RICH The DELPHI Oine Analysis Chain A Threejet Event Recorded with the DELPHI Detector Performance of the DELPHI bTagging Package Inclusive B Reconstruction Algorithm Performance of the Inclusive B Reconstruction Iterative Pro cedure for the Vertex Reconstruction Selected b b Event in DELPHI Performance of the Vertex Reconstruction Algorithm Sp ecic Energy Loss dE dx in the TPC Average Cherenkov Angle p er Track for Liquid and Gas RICH Performance of the DELPHI Hadron Identication Qvalue Distribution for B Pairs Comparison of the B Qvalue Distribution with Various Mo dels Qvalue Distribution for B Pairs in HelicityBins Decay Angle Distribution for B Pions Decay Angle Distribution B Signal sub divided Decay Characteristics for the Four B Charge States Qvalue Distribution for the Four B Charge States Total Pro duction Cross Section b B Inclusive B Cross Section in Bins of x Etrue Decay Characteristics for the Two B Charge States s QuarkFlavour Tagging for B Decays s Distribution of the Qvalue of B K Pairs Distribution of the Qvalue of B K Pairs Jet Charge Anticut Distribution of the Qvalue of Pairs with and without Baryon Enrichment b Distribution of the Qvalue of Pairs with DierentBaryon Enrichments b Decay Characteristics for the Four Charge States b Distribution of the Qvalue of B Pairs for the Dierent Charge States Decay Angle Distribution for Pions b List of Tables Additive Quantum Numb ers of the Quarks Selected Exp erimental Results on B and B Mesons Excitation Sp ectrum in the Static Quark Mo del Exp erimental Results for Orbitally Excited D Mesons D Pro duction in e e Annihilation Prop erties of and Baryons b b Numb er of Multihadronic and bb Events in DELPHI Cherenkov Angle Reconstruction in the RICH Detectors Dierential Pro duction Cross Section d d cos b Total Pro duction Cross Section B b Dierential Pro duction Cross Section d dx b Etrue LEP B B Results ud LEP B B K Results s LEP Results b b Chapter Intro duction The present knowledge of particle physics considers the observed matter in the surrounding nature to b e constructed from six dierenttyp es of quarks and leptons The quark typ es are called d u s c b and t the lepton typ es are called e and Quarks and e leptons are fermions with spin The fundamental interactions b etween these particles are understo o d by the exchange of socalled gauge b osons The describing theory is known as the Standard Mo del of particle physics It basically consists of the following The theory of strong interactions which is called Quantum Chromo dynamics QCD de scrib es the eects of quark interactions The gauge b osons of the strong interaction the gluons have b een discovered in threejet events at the electronp ositron ring PETRA at DESY Since the gluon carries colour charge this leads to the observed quarkgluon conne mentatlower energies Because of this eect the theory QCD has to b e a nonAb elian theory The theory of the electroweak interactions has b een develop ed by Glashow Salam and Weinb erg It
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