Measurements of charged-particle distributions with the ATLAS detector

TL;DR

This paper reports detailed measurements of charged-particle distributions at 8 TeV and 13 TeV energies using the ATLAS detector, providing new insights into non-perturbative QCD and challenging existing Monte Carlo models.

Contribution

First comprehensive charged-particle distribution measurements at 8 TeV and 13 TeV with low transverse momentum thresholds in various phase space regions by ATLAS.

Findings

Measurements challenge existing Monte Carlo predictions

Some phase space regions studied for the first time by ATLAS

Data provide strong constraints on QCD models

Abstract

Inclusive charged-particle measurements probe the low-energy region of the non-perturbative quantum chromodynamics. The ATLAS collaboration has recently measured the charged-particle multiplicity and its dependence on transverse momentum and pseudorapidity in special data sets with low LHC beam currents, recorded at centre-of-mass energies of 8 TeV and 13 TeV. The measurements at 8 TeV cover a wide spectrum using charged-particle selections with minimum transverse momentum of both 100 MeV and 500 MeV and in various phase space regions of low and high charged-particle multiplicities, some of which are studied for the first time by ATLAS. The measurements at 13 TeV also present detailed studies with a minimum transverse momentum of both 100 MeV and 500 MeV. The measurements are compared with predictions of various tuned Monte Carlo generators and are found to provide strong constraints on these. None of the Monte Carlo generators with their respective tunes are able to reproduce all the features of the data.