Study of charm production in Z decays

Abstract

The production rates of D*±, D*±s, D±, D0/D̄0, D±s, and Λ+c / Λ̄-c in Z → cc̄ 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 → D*+) = 0.233 ± 0.010 (stat.) ± 0.011(syst.). The average fraction of the beam energy carried by D*± mesons in Z → cc̄ events is measured to be 〈XE(D*±)〉cc̄ = 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 cc̄ pair: n̄g → cc̄ = (3.23 ± 0.48(stat.) ± 0.53(syst.))%. The ratio of the Vector/(Vector+Pseudoscalar) production rates in charmed mesons is found to be PV = 0.595 ±0.045. The fractional decay width of the Z into cc̄ 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.).