Measurements of the Z partial decay width into cc-bar and multiplicity of charm quarks per b decay

摘要

The partial decay width R_c of the Z into cc-bar quark pair and the number of charm quarks n_c per b decay are measured with the DELPHI detector at LEP 1. Particle identification provides clear D~0, D~+, D_s~+ and Λ_c~+ signatures. The charm hadron production rate is measured in each channel by a fit to the scaled energy, impact parameter information and the invariant mass spectrum. Two measurements of R_c are presented, from the D~(*+) production rate and from the overall charm counting, including strange charm baryon production, in cc-bar events. The multiplicity n_c, which includes hidden cc-bar and strange charm baryon production, is inferred from the charm counting in bb-bar events. The final results are R_c = 0.1665 ± 0.0095 and n_c = 1.166 ± 0.086.