Soft and semihard components of multiplicity distributions in the $k_T$ factorization approach

TL;DR

This paper investigates the soft and semihard components of particle multiplicity distributions in hadronic collisions using the $k_T$ factorization approach, highlighting how semihard events influence observed scaling violations.

Contribution

It introduces a scale-based separation of soft and semihard events within the $k_T$ factorization framework and analyzes their impact on multiplicity distributions and KNO scaling.

Findings

Growth of semihard events with energy affects multiplicity distributions.

Correlation between semihard event fraction and KNO scaling violation.

Quantitative estimates of particle production in different regimes.

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 with in perturbative QCD the former contains non-perturbative 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 note we revisit the separation between soft and semihard events using the formalism of $k_T$ factorization. The separation is implemented through the introduction of a scale that is the cutoff $\Lambda$ 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 KNO scaling.