Abstract
The antiparticle-over-particle multiplicity ratio is measured in deep-inelastic scattering for negatively and positively charged kaons and, for the first time, for antiprotons and protons. The data were obtained by the COMPASS Collaboration using a 160 GeV muon beam impinging on an isoscalar 6LiD target.
The regime of deep-inelastic scattering is ensured by requiring Q^2 > 1 (GeV/c)^2 for the photon virtuality and W > 5 GeV/c^2 for the invariant mass of the produced hadronic system. Bjorken-x is restricted to the range 0.01 to 0.40.
Protons and antiprotons are identified in the momentum range from 20 GeV/c to 60 GeV/c and required to carry a large fraction of the virtual-photon energy, z > 0.5. In the whole studied z-region, the p bar over p multiplicity ratio is found to be below the lower limit expected from calculations based on leading-order perturbative Quantum Chromodynamics (pQCD).
Kaons were previously analysed in the momentum range 12 GeV/c to 40 GeV/c. In the present analysis this range is extended up to 55 GeV/c, whereby events with larger virtual-photon energies are included in the analysis and the observed K- over K+ ratio becomes closer to the expectation of next-to-leading order pQCD.
The results of both analyses strengthen our earlier conclusion that at COMPASS energies the phase space available for single-hadron production in deep-inelastic scattering should be taken into account in the standard pQCD formalism.