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.

Original languageEnglish
Article number135600
JournalPhysics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
StatePublished - 10 Aug 2020


FundersFunder number
Daiko and Yamada Foundations
National Science Foundation1506416, 283286, PHY-1506416
National Science Foundation
Seventh Framework Programme
European Commission
Deutsche Forschungsgemeinschaft
Japan Society for the Promotion of Science18002006, 20540299, 26247032, 18540281
Japan Society for the Promotion of Science
Ministry of Education, Culture, Sports, Science and Technology
Ministerstvo Školství, Mládeže a TělovýchovyLM20150581
Ministerstvo Školství, Mládeže a Tělovýchovy
Fundação para a Ciência e a TecnologiaCERN/FIS-PAR/0022/2019, CERN/FIS-PAR/0007/2017
Fundação para a Ciência e a Tecnologia
Bundesministerium für Bildung und Forschung
Israel Academy of Sciences and Humanities0.1764
Israel Academy of Sciences and Humanities
LabexANR-10-LABX-0038, ANR-11-IDEX-0003-01
Narodowe Centrum Nauki2017/26/M/ST2/00498
Narodowe Centrum Nauki
Ministry of Science and Technology, Taiwan


    • Deep-inelastic scattering
    • Hadron multiplicities
    • Quantum chromodynamics
    • pQCD


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