I= A STUDY OF BEAUTY PRODUCTION IN Z DECAYS USING DIFFERENT FRAGMENTATION MODELS
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Title of Thesis
A STUDY OF BEAUTY PRODUCTION IN Z DECAYS USING DIFFERENT FRAGMENTATION MODELS

Author(s)
Khalid Nadeem Qureshi
Institute/University/Department Details
Department of Physics/ Quaid-i-Azam University, Islamabad
Session
1995
Subject
Physics
Number of Pages
103
Keywords (Extracted from title, table of contents and abstract of thesis)
beauty production, z decays, fragmentation models, qq events, z peak

Abstract
The properties of Z †’ bb) decays and the inclusive semileptonic branching ratio, Br(b -†’ lvX), have been measured by studying inclusive lepton events using =293 K hadronic events recorded with the L3 detector at LEP at VS = mz. Model dependence of the observables, the partial decay width of the Z into bb (T bb), Br(b -†’ lvX) and the average scaled energy, , of the b-hadrons have been investigated by simulating the process e+e- †’ Z †’ hadrons using the JETSET, HERWIG and EURODEC Monte Carlo programmes. JETSET and HERWIG are qq event generators which are based upon string and cluster fragmentation models respectively. EURODEC is a particle decay package and is interfaced with these qq event generators. Thus the fragmentation and decay model dependence of the above observables was investigated. In addition the systematic effects of other sources of errors were also studied. The results of the measurements are:

T bb = 386 ± 4(stat.) ± lO(frag.) ± 9(dec.) ± 21(sys.) MeV (1) Br(b -†’ lvX) = 11.81 ± 0.48(stat.) ± 0.28(frag.) ± 0.18(dec.) ± 0.79(sys.) % (2) Br(b -†’ lvX) =12.01 ± 0.15(stat.) ± 0.33(frag.) ± 0.36(dec.) ± 0.45(sys.) % (3) =0.6953 ± 0.0038(stat.) ± 0.0006(frag.) ± 0.0002(dec.) ± 0.0078(sys.) (4) =0.6954 ± 0.0033(stat.) ± 0.0024(dec.) ± 0.0078(sys.) (5)

where the errors are due to statistics, fragmentation model, b-hadron decay model and other systematics respectively. Measurement (2) was made using the 'ratio of the observed number of dilepton events to single lepton events, and is almost independent of T bb. Measurement (3) was made by assuming the Standard Model prediction of T bb = 378 ± 3 Me V. Measurement (4) was made by performing a model independent fit, while for measurement (5) fragmentation function given by Peters on et al. was assumed.

On the basis of analysis presented in this work it is concluded that the simulations of qq events based upon these models, well describe the observed production and decay properties of the beauty at and around the Z peak.

Download Full Thesis
2400.37 KB
S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents 0
136.49 KB
2 1 Introduction 7
55.07 KB
3 2 Theoretical Overview 9
262.43 KB
  2.1 Basic Concepts of Standard Model 9
  2.2 The Process e+ e- †’ hadrons 12
4 3 The Apparatus 23
541.38 KB
  3.1 The LEP Collider 23
  3.2 The L3 Detector 25
5 4 Monte Carlo Simulation 39
261.59 KB
  4.1 Event Simulation 39
  4.2 JETSET 40
  4.3 EURODEC 43
  4.4 HERWIG 44
  4.5 Summery of Generator 47
  4.6 Detector of simulation 48
6 5 Reconstruction and Selection 50
494.14 KB
  5.1 Event Reconstruction 50
  5.2 Signature of a b-hadron 51
  5.3 Event Selection 53
  5.4 Data Sample 61
  5.5 Detector Effects 68
7 6 Fitting and Results 70
527.88 KB
  6.1 Fitting Strategy 70
  6.2 Measurement Results 75
  6.3 Measurement of Br( b - †’ l vX ) 76
8 7 Conclusion 89
248.53 KB
  7.1 Appendix A Study of Systematics 91
  7.2 Bibliography 94