The K over K+ multiplicity ratio is measured in deep-inelastic scattering, for the first time for kaons carrying a large fraction z of the virtual-photon energy. The data were obtained by the COMPASS collaboration using a 160 GeV muon beam and 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>5GeV/c2 for the invariant mass of the produced hadronic system. Kaons are identified in the momentum range from 12 GeV/c to 40 GeV/c, thereby restricting the range in Bjorken-x to 0.01<x<0.40. The z-dependence of the multiplicity ratio is studied for z>0.75. For very large values of z, i.e. z>0.8, we observe the kaon multiplicity ratio to fall below the lower limits expected from calculations based on leading and next-to-leading order perturbative quantum chromodynamics. Also, the kaon multiplicity ratio shows a strong dependence on the missing mass of the single-kaon production process. This suggests that within the perturbative quantum chromodynamics formalism an additional correction may be required, which takes into account the phase space available for hadronisation.

Original languageEnglish
Pages (from-to)390-398
Number of pages9
JournalPhysics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
StatePublished - 10 Nov 2018


FundersFunder number
National Science FoundationPHY-1506416
National Science Foundation
California Department of Fish and Wildlife
Ministry of Science and Technology
Seventh Framework Programme283286
Seventh Framework Programme
Deutsche Forschungsgemeinschaft
Bundesministerium für Bildung und Forschung
Ministry of Education, Youth and ScienceLG13031
Ministry of Education, Youth and Science
Israel Academy of Sciences and Humanities
Narodowym Centrum Nauki2015/18/M/ST2/00550
Narodowym Centrum Nauki
Fundació Catalana de Trasplantament123600/2011, CERN/FP 116376/2010, CERN/FIS-NUC/0017/2015
Fundació Catalana de Trasplantament


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