Emergence of Koba-Nielsen-Olsen scaling in multiplicity distributions in jets produced at the LHC

Abstract

In this work we study the multiplicity distributions (MDs) of charged particles within jets in proton-proton collisions, which were measured by the ATLAS Collaboration in 2011, 2016 and 2019. The first dataset refers to jets with smaller transverse momenta (4<pT<40  GeV) whereas the other two refer to higher pT jets (0.1<pT<2.5  TeV). We find that the lower pT set shows no sign of KNO scaling and that the higher pT sets gradually approach the scaling limit. For the lower pT set the mean multiplicity as a function of pT can be well-described by expressions derived from QCD with different approximation schemes. For higher (>500  GeV) values of pT these expressions significantly overshoot the data. We show that the behavior of the MDs can be well-represented by a sub-Poisson distribution with energy dependent parameters. In the range 40<pT<100  GeV there is a transition from sub to super Poissonian behavior and the MD evolves to a geometric distribution, which shows KNO scaling. In this way we fit the MDs in all transverse momentum intervals with one single expression. We discuss the implications of this phenomenological finding. Published by the American Physical Society 2024