2018 Impact factor 4.843
Particles and Fields
Eur. Phys. J. C 16, 597-611
DOI 10.1007/s100520000421

Study of charm production in Z decays

The ALEPH Collaboration

R. Barate - et al.

Laboratoire de Physique des Particules (LAPP), IN2P3-CNRS, 74019 Annecy-le-Vieux Cedex, France

Received: 21 September 1999 / Published online: 8 June 2000 - © Springer-Verlag 2000

Abstract
The production rates of ${\mathrm{D}}^{*\pm}$, ${\mathrm{D}}_{\rm {s}}^{* \pm}$, ${\mathrm{D}}^{\pm}$, ${\mathrm{D}}^0 /
\bar{{\mathrm{D}}}^0$, ${\mathrm{D}}_{\rm {s}}^{\pm}$, and $\Lambda_{\rm {c}}^{+}/{\bar{\Lambda}}_{\rm {c}}^{-}$ in ${{\mathrm{Z}}}\rightarrow
{\mathrm{c}} \bar{{\mathrm{c}}}$ decays are measured using the LEP I data sample recorded by the ALEPH detector. The fractional energy spectrum of the ${\mathrm{D}}^{*\pm}$ is well described as the sum of three contributions: charm hadronisation, b hadron decays and gluon splitting into a pair of heavy quarks. The probability for a c quark to hadronise into a D*+ is found to be $f({\mathrm{c}} \to {\mathrm{D}}^{*+})
= 0.233 \pm 0.010 \mathrm{(stat.)} \pm 0.011 \mathrm{(syst.)}$. The average fraction of the beam energy carried by ${\mathrm{D}}^{*\pm}$ mesons in ${{{\mathrm{Z}}}\to {\mathrm{c}} \bar{{\mathrm{c}}}}$ events is measured to be ${\langle X_E
({\mathrm{D}}^{*\pm}) \rangle}_{{\mathrm{c}} \bar{{\mathrm{c}}}} = 0.4878 \pm 0.0046
\mathrm{(stat.)} \pm 0.0061 \mathrm{(syst.)}.$ The ${\mathrm{D}}^{*\pm}$ energy and the hemisphere mass imbalance distributions are simultaneously used to measure the fraction of hadronic Z decays in which a gluon splits to a ${\mathrm{c}} \bar{{\mathrm{c}}}$ pair: $\bar{n}_{\mathrm{g} \to {\mathrm{c}} \bar{{\mathrm{c}}}} = (3.23 \pm 0.48 \mathrm{(stat.)} \pm 0.53
\mathrm{(syst.)})\%.$ The ratio of the Vector/(Vector+Pseudoscalar) production rates in charmed mesons is found to be $P_V =
0.595\pm0.045$. The fractional decay width of the Z into ${\mathrm{c}} \bar{{\mathrm{c}}}$ pairs is determined from the sum of the production rates for various weakly decaying charmed states to be ${{\mathrm{R}}_{{\mathrm{c}}}}= 0.1738 \pm 0.0047 {\rm (stat.)} \pm 0.0116 {\rm
(syst.)}.$


Copyright Società Italiana di Fisica, Springer-Verlag 2000