Charged-particle multiplicity distributions over a wide pseudorapidity range in p-Pb collisions at $\mathbf{\sqrt{s}_{\rm NN} = 5.02}$ TeV

TL;DR

This study measures charged-particle multiplicity distributions in p-Pb collisions at 5.02 TeV, analyzing their shape, moments, and evolution, and compares results with models and other collision systems.

Contribution

It provides detailed multiplicity distributions over a wide pseudorapidity range and evaluates model descriptions, highlighting discrepancies and the energy dependence of particle production.

Findings

Distributions are well described by a double negative binomial function.

Models fail to reproduce the shape evolution of the distributions.

Charged-particle multiplicity increases with collision energy, consistent across systems.

Abstract

This paper presents the primary charged-particle multiplicity distributions in proton-lead collisions at a centre-of-mass energy per nucleon-nucleon collision of $\sqrt{s_{\rm NN}} = 5.02$ TeV. The distributions are reported for non-single diffractive collisions in different pseudorapidity ranges. The measurements are performed using the combined information from the Silicon Pixel Detector and the Forward Multiplicity Detector of ALICE. The multiplicity distributions are parametrised with a double negative binomial distribution function which provides satisfactory descriptions of the distributions for all the studied pseudorapidity intervals. The data are compared to models and analysed quantitatively, evaluating the first four moments (mean, standard deviation, skewness, and kurtosis). The shape evolution of the measured multiplicity distributions is studied in terms of KNO variables and it is found that none of the considered models reproduces the measurements. This paper also reports on the average charged-particle multiplicity, normalised by the average number of participating nucleon pairs, as a function of the collision energy. The multiplicity results are then compared to measurements made in proton-proton and nucleus-nucleus collisions across a wide range of collision energies.