Charged particle multiplicities in heavy and light quark initiated events above the Z0 peak

TL;DR

This study measures charged particle multiplicities in different quark events at LEP energies, confirming QCD predictions of energy independence in multiplicity differences between heavy and light quarks.

Contribution

It provides the first comprehensive measurement of multiplicity differences across a wide energy range, testing QCD against phenomenological models.

Findings

The multiplicity difference delta_bl is energy independent.

Results support QCD predictions over phenomenological models.

Measured delta_bl at 195 GeV is 3.44+-0.40(stat)+-0.89(syst).

Abstract

We have measured the mean charged particle multiplicities separately for bbbar, ccbar and light quark (uubar, ddbar, ssbar) initiated events produced in e+e- annihilations at LEP. The data were recorded with the OPAL detector at eleven different energies above Z0 peak, corresponding to the full statistics collected at LPE1.5 and LEP2. The difference in mean charged and particle multiplicities for bbbar and light quark events, delta_bl, measured over this energy range is consistent with an energy independent behaviour, as predicted by QCD, but is inconsistent with the prediction of a more phenomenological approach which assumes that the multiplicity accompanying the decay of a heavy quark is independent of the quark mass itself. Our results, which can be combined into the single measurement delta_bl = 3.44+-0.40(stat)+-0.89(syst) at a luminosity weighted average centre-of mass energy of 195 GeV, are also consistent with an energy independent behaviour as extrapolated from lower energy data.