Antiproton over proton and K− over K+ multiplicity ratios at high z in DIS

Le résumé fourni par la source

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 6 LiD 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 ¯ 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.

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