Nuclear Modification Factor in Small System Collisions within Perturbative QCD Including Thermal Effects

TL;DR

This study investigates nuclear modification factors for pion production in small system collisions at RHIC, incorporating thermal effects and collective expansion within a perturbative QCD framework, revealing insights into particle suppression and soft sector behavior.

Contribution

It introduces a combined perturbative QCD and thermal model approach to analyze nuclear modification factors in small systems, accounting for collective expansion and soft particle multiplicities.

Findings

Evidence of thermal effects and collective expansion in pion production.

Dependence of nuclear modification factors on centrality and projectile species.

Observation of Cronin peak behavior and suppression at high transverse momentum.

Abstract

In this paper, dedicated to the memory of the late Prof. Jean Cleymans, the nuclear modification factors, $R_{xA}$, are investigated for pion production in small system collisions, measured by PHENIX experiment at RHIC (Relativistic Heavy Ion Collider). The theoretical framework is the transverse momentum $k_T$-factorization formalism for hard processes at small momentum fraction, $x$. Evidence for collective expansion and thermal effects for pions, produced at equilibrium, is studied based on phenomenological parametrization of blast-wave type in the relaxation time approximation. The dependencies on the centrality and on the projectile species are discussed in terms of the behavior of Cronin peak and the suppression of $R_{xA}$ at large transverse momentum, $p_T$. The multiplicity of produced particles, which is sensitive to the soft sector of the spectra, is also included in the present analysis.