Where Does the Energy Loss Lose Strength?

TL;DR

This paper investigates the suppression of high transverse momentum pion production in heavy-ion collisions, attributing it mainly to initial state nuclear effects and jet-energy loss, with implications for understanding quark-gluon plasma properties.

Contribution

It provides a detailed analysis of nuclear modification factors at very high p_T, incorporating initial state effects and jet quenching, and compares results between RHIC and LHC energies.

Findings

R_{AA}(p_T) drops below 1 at high p_T due to combined effects.

Initial state nuclear modifications significantly influence suppression.

Larger opacity values are needed to describe LHC collision data.

Abstract

Nuclear modification factors for pion production in AuAu and CuCu collisions are analyzed at very high transverse momenta. At p_T > 10 GeV/c, the R_{AA}(p_T) is determined mostly by the initial state nuclear modifications (e.g. EMC effect) and the non-Abelian jet-energy loss in the final state. At high momenta these effects together are strong enough to suppress R_{AA}(p_T) to below 1 at RHIC energies. We display results using HKN shadowing in our pQCD improved parton model. Result of a similar calculation at LHC energies for PbPb collisions are also displayed. Based on dN/dy estimates, a larger opacity value, L/\lambda_g = 10 +/- 2, is used for the produced partonic matter in central collisions at the LHC.