Abstract
We have measured the mean charged particle multiplicities separately for bb̄, cc̄ and light quark (uū,dd̄,ss̄) initiated events produced in e+e− annihilations at LEP. The data were recorded with the OPAL detector at eleven different energies above the Z0 peak, corresponding to the full statistics collected at LEP1.5 and LEP2.The difference in mean charged particle multiplicities for bb̄ and light quark events, δbl, 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 δbl=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.
Highlights
The study of heavy quark pair production in e+e−collisions with centre-of-mass energies greatly exceeding the heavy quark masses provides important tests of perturbative QCD
For a recent review see for example [4]. This prediction is in striking contrast with that from a more phenomenological approach, the so-called naıve model [5, 6], which assumes that the hadron multiplicity accompanying the heavy hadrons in bbevents is the same as the multiplicity in light quark events at the energy left to the system once the heavy quarks have fragmented
The estimated events with a true residual 4-fermion effective centre-of-mass energy background varies from 2.4%, 2The main changes from the default tune are that meson states that do not belong to the L = 0, 1 supermultiplets are removed, and that the parameters CLSMR(1), PSPLT(2) and DECWT have been changed from their default values of 0.0, 1.0, and 1.0 to 0.4, 0.33, and 0.7
Summary
The study of heavy quark pair production in e+e−collisions with centre-of-mass energies greatly exceeding the heavy quark masses provides important tests of perturbative QCD. For a recent review see for example [4] This prediction is in striking contrast with that from a more phenomenological approach, the so-called naıve model [5, 6], which assumes that the hadron multiplicity accompanying the heavy hadrons in bbevents is the same as the multiplicity in light quark events at the energy left to the system once the heavy quarks have fragmented. The numbers of events collected at these higher energies are much smaller than at LEP1, and the results will be much less precise In this analysis we have measured the mean charged particle multiplicity separately for b, c and uds initiated event√s observed with th√e OPAL detector at all eleven LEP energies above the Z0 resonance, ranging from s = 130 GeV to s = 206 GeV, and derived at each energy the difference δbl. Their measured values of δbl were found to be consistent with an energy independent extrapolation from lower energy data, and inconsistent with the prediction of the naıve model by more than three standard deviations
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