Emergence of KNO scaling in multiplicity distributions in jets produced at the LHC

TL;DR

This study investigates charged particle multiplicity distributions in jets at the LHC, revealing a transition to KNO scaling at high transverse momenta and modeling the distributions with a unified phenomenological approach.

Contribution

It demonstrates the emergence of KNO scaling in high-$p_T$ jets and introduces a unified model describing multiplicity distributions across different energy regimes.

Findings

KNO scaling appears in high-$p_T$ jets above 500 GeV.

Multiplicity distributions transition from sub-Poisson to geometric distribution.

A single phenomenological expression fits all transverse momentum intervals.

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 data set refers to jets with lower transverse momenta ($4 < p_T < 40$ GeV ) whereas the other two refer to higher $p_T$ jets ($0.1 < p_T < 2.5$ TeV). We find that the first set shows no sign of KNO scaling whereas the higher $p_T$ sets gradually approach the scaling limit. In the first set the mean multiplicity as a function of $p_T$ can be well described by expressions derived from QCD with different approximation schemes. For higher ($> 500$ GeV) values of $p_T$ 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 $40 < p_T < 100$ 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.