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 Q2 > 1 (GeV/c)2 for the photon virtuality and W>5 GeV/c2 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.
Highlights
Within the standard approach of perturbative Quantum Chromodynamics, hadron production from an active quark in a deep-inelastic scattering process (DIS) is effectively described by non-perturbative objects called fragmentation functions (FFs).These functions presently cannot be predicted by theory, but their scale evolution is described by the DGLAP equations [1]
In order to provide more experimental results for further phenomenological studies, we present here for the first time the COMPASS results on the pover p multiplicity ratio Rp at high z, i.e. z > 0.5, which are obtained from semiinclusive measurements of deep-inelastic lepton-nucleon scattering (SIDIS) data taken on an isoscalar target
It is remarkable that Rp falls below the leading order (LO) perturbative Quantum Chromodynamics (pQCD) prediction over the whole measured z range, which starts in this analysis from z > 0.5
Summary
Within the standard approach of perturbative Quantum Chromodynamics (pQCD), hadron production from an active quark in a deep-inelastic scattering process (DIS) is effectively described by non-perturbative objects called fragmentation functions (FFs). These functions presently cannot be predicted by theory, but their scale evolution is described by the DGLAP equations [1]. From the measured ν-dependence it was concluded that in experiments with similar (or lower) centre-of-mass energy than COMPASS an insufficient description of the data by pQCD may affect the region of high and medium values of z These kinematic regions are important in many respects, as e.g. transverse-momentum-dependent azimuthal asymmetries are quite pronounced there [13].
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