Study of Charm Production in Z Decays

TL;DR

This paper measures charm hadron production rates, energy spectra, and gluon splitting probabilities in Z decays to cc pairs using ALEPH data, providing detailed insights into charm quark hadronization and decay.

Contribution

It offers new precise measurements of charm production fractions, energy distributions, and gluon splitting rates in Z decays, enhancing understanding of charm quark dynamics.

Findings

Charm hadronization probability f(c to D*+) = 0.233 ± 0.015

Average D*+- energy fraction in Z to cc events = 0.4878 ± 0.0077

Gluon splitting to cc pairs rate = (3.23 ± 0.72)%

Abstract

The production rates of D*+-, Ds*+-, D+-, D0 / D0bar, Ds+, and Lambda_c in Z to ccbar decays are measured using the LEP I data sample recorded by the ALEPH detector. The fractional energy spectrum of the D*+- 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(c to D*+) = 0.233 +- 0.010 (stat.) +- 0.011 (syst.). The average fraction of the beam energy carried by D*+- mesons in Z to cc events is measured to be < X_E (D*+-) >_cc = 0.4878 +- 0.0046 (stat.) +- 0.0061 (syst.). The D*+- 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 cc pair: n_{gluon to cc} = (3.23 +- 0.48 (stat.) +- 0.53 (syst.) %. The ratio of the Vector/(Vector+Pseudoscalar) production rates in charmed mesons is found to be P_V = 0.595 +- 0.045. The fractional decay width of the Z into cc pairs is determined from the sum of the production rates for various weakly decaying charmed states to be Rc = 0.1738 +- 0.0047 (stat.) +- 0.0116 (syst.).