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Soft and semihard components of multiplicity distributions in the kT-factorization approach

H. R. Martins-Fontes* and F. S. Navarra†

  • *Contact author: henriquemartinsfontes@usp.br
  • †Contact author: navarra@if.usp.br
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Phys. Rev. D 112, 094045 – Published 24 November, 2025

DOI: https://doi.org/10.1103/wcld-3j5q

Abstract

Particle production in hadronic collisions can be studied in the low-momentum (soft) and high-momentum (hard) transfer regimes. While the latter can be well understood within perturbative QCD, the former contains nonperturbative effects which cannot be calculated from first principles. There is also an intermediate regime called semihard, in which the momentum transfer runs typically from 1 to 10 GeV. As the hadron-hadron collision energy increases, we expect to see a relative growth of the number of semihard events. It has been conjectured that this growth would be the cause of some changes observed in the multiplicity distributions measured in proton-proton collisions. In this paper we revisit the separation between soft and semihard events using the formalism of kT factorization. The separation is implemented through the introduction of a scale that is the cutoff Λ in the transverse momentum of the produced gluon and allows us to compute the average number of particles produced in each regime. These numbers are used as input in the double negative binomial fit of data, from which we can extract correlations between the fraction of semihard events and the violation of Koba-Nielsen-Olsen scaling.

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Phys. Rev. D 112, 094045– Published 24 November, 2025
  • Received 30 June 2025
  • Accepted 28 October 2025
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