Multiplicity and pseudorapidity density distributions of charged particles produced in pp, pA and AA collisions at RHIC \& LHC energies

TL;DR

This paper analyzes charged particle pseudorapidity distributions in various high-energy collisions, extrapolates data to full kinematic ranges, and tests models of particle production, revealing participant-scaling violations at TeV energies.

Contribution

It introduces three ansätze to describe pseudorapidity distributions across different collision systems and energies, and provides predictions for future collider experiments.

Findings

Evidence for participant-scaling violations at TeV energies

Constraints on initial condition models for particle production

Predictions for charged particle multiplicities at future colliders

Abstract

Multiplicity and pseudorapidity ($\eta$) density ($dN_{\rm ch}/d\eta$) distributions of charged hadrons provide key information towards understanding the particle production mechanisms and initial conditions of high-energy heavy-ion collisions. However, detector constraints limit the $\eta$-range across which charged particle measurements can be carried out. Extrapolating the measured distributions to large $\eta$-range by parameterizing measured distributions and by using calculations from event generators, we characterize the production of charged particles over the full kinematic range. In the present study, we use three different ans$\ddot{\mathrm a}$tze to obtain quantitative descriptions of the shape of pseudorapidity distributions of charged hadrons produced in pp, p-A, and A-A collisions for beam energies ($\sqrt{s_{\rm NN}}$) ranging from a few GeV to a few TeV corresponding to RHIC and LHC energies. We study the limiting fragmentation behavior in these collisions and report evidence for participant-scaling violations in high-energy collisions at the TeV scale. We additionally examine measured pseudorapidity distributions to constrain models describing initial conditions of particle production. We predict the centrality dependence of charged particle multiplicity distributions at FAIR and NICA energies and give an estimation of charged particle multiplicity at $\eta=0$ for the proposed HE-LHC and FCC energies.