Leading-particle suppression in high energy nucleus-nucleus collisions

TL;DR

This paper addresses leading-particle suppression in high-energy nucleus-nucleus collisions as a probe of parton energy loss in a dense QCD medium. The authors implement the Parton Quenching Model (PQM) using the BDMPS quenching weights within a Glauber-based collision geometry, computing the energy-loss probability $P(\Delta E;R,\omega_c)$ from a local transport coefficient $\hat{q}(\xi)$ along each parton's path, thereby determining effective $\omega_c$ and $R$ on a per-parton basis. The model contains a single free parameter, fixed to central $R_{AA}$ at $\sqrt{s_{\rm NN}}=200$ GeV, and is then used to predict the centrality dependence of $R_{AA}$, the suppression of away-side jet-like correlations $I_{AA}$, and the azimuthal anisotropy $v_2$, with extrapolations to $\sqrt{s_{\rm NN}}=62.4$ GeV and $5.5$ TeV. Key findings include a large effective $\langle \hat{q} \rangle \simeq 14~\mathrm{GeV}^2/\mathrm{fm}$ in central RHIC collisions, substantial parton absorption with $\langle \Delta E/E \rangle$ approaching unity (especially for gluons), and a prediction at LHC of a nearly $p_T$-independent, strong suppression $R_{AA} \approx 0.15$ in central events, driven by surface-emission geometry. The analysis also discusses finite-energy corrections via non-reweighted and reweighted schemes, illustrating theoretical uncertainties in finite-energy parton treatments within the eikonal limit.

Abstract

Parton energy loss effects in heavy-ion collisions are studied with the Monte Carlo program PQM (Parton Quenching Model) constructed using the BDMPS quenching weights and a realistic collision geometry. The merit of the approach is that it contains only one free parameter that is tuned to the high-pt nuclear modification factor measured in central Au-Au collisions at sqrt{s_NN} = 200 GeV. Once tuned, the model is coherently applied to all the high-pt observables at 200 GeV: the centrality evolution of the nuclear modification factor, the suppression of the away-side jet-like correlations, and the azimuthal anisotropies for these observables. Predictions for the leading-particle suppression at nucleon-nucleon centre-of-mass energies of 62.4 and 5500 GeV are calculated. The limits of the eikonal approximation in the BDMPS approach, when applied to finite-energy partons, are discussed.