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

Abstract

In this paper, the nuclear modification factors, RxA, are investigated for pion production in small system collisions, measured by PHENIX experiment at RHIC (Relativistic Heavy Ion Collider). The theoretical framework is the parton transverse momentum kT-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 RxA at large transverse momentum, pT. The multiplicity of produced particles, which is sensitive to the soft sector of the spectra, is also included in the present analysis.

Keywords

• <i>k_T</i>-factorization approach
• parton saturation phenomenon
• geometric scaling in hadron–hadron collisions
• high-energy collisions
• multiparticle production
• transverse momentum distribution