Multiplicity of charged and neutral pions in deep-inelastic scattering of 27.5 GeV positrons on hydrogen

Abstract

Measurements of the individual multiplicities of π^+, π^− and π^0 produced in the deep-inelastic scattering of 27.5 GeV positrons on hydrogen are presented. The average charged pion multiplicity is the same as for neutral pions, up to z≈0.7, where z is the fraction of the energy transferred in the scattering process carried by the pion. This result (below z≈0.7) is consistent with isospin invariance. The total energy fraction associated with charged and neutral pions is 0.51±0.01(stat.)±0.08 (syst.) and 0.26±0.01(stat.)±0.04(syst.), respectively. For fixed z, the measured multiplicities depend on both the negative squared four momentum transfer Q^2 and the Bjorken variable x. The observed dependence on Q^2 agrees qualitatively with the expected behaviour based on NLO-QCD evolution, while the dependence on x is consistent with that of previous data after corrections have been made for the expected Q^2 -dependence.

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