Measurements of the Z partial decay width into \(c\bar c\) and multiplicity of charm quarks per b decay

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The partial decay width \(R_c\) of the Z into \(c\bar c\) 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 \(\Lambda_c^+\) 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 \(c\bar c\) events. The multiplicity \(n_c\) , which includes hidden \(c\bar c\) and strange charm baryon production, is inferred from the charm counting in \(b\bar{b}\) events. The final results are \(R_c = 0.1665 \pm 0.0095\) and \(n_c = 1.166 \pm 0.086\) .

Received: 1 June 1999 / Published online: 8 December 1999