A STUDY OF BEAUTY PRODUCTION IN Z DECAYS USING DIFFERENT FRAGMENTATION MODELS

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:\ud \ud 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)\ud \ud 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.\ud \ud 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