Parton-medium interaction from RHIC to LHC - a systematic approach

TL;DR

This paper discusses the challenges in distinguishing different parton-medium interaction models in heavy-ion collisions at RHIC and LHC, emphasizing the importance of combined data analysis for better discrimination.

Contribution

It introduces a systematic approach to compare models using data from both RHIC and LHC, highlighting the increased discriminative power at LHC energies.

Findings

Spectral shape differences affect model discrimination.

Combined RHIC and LHC data improve model differentiation.

Energy loss models are mainly constrained near zero energy loss.

Abstract

Despite a wealth of experimental data for high p_T processes in heavy-ion collisions, discriminating between different models of hard parton-medium interactions has been difficult. One important reason is that the pQCD parton spectrum at RHIC kinematics is so steeply falling that distinguishing even a moderate shift in parton energy from complete parton absorption is almost impossible in observable quantities. In essence, energy loss models are effectively only probed in the vicinity of zero energy loss and as a result, only the pathlength dependence of energy loss offers some discriminating power at RHIC kinematics. At LHC, this is no longer the case: Due to the much flatter shape of the parton spectra originating from 2.76 AGeV collisions, the available observables probe much deeper into the model dynamics. A simultaneous fit of the nuclear suppression both at RHIC and LHC kinematics has thus a huge potential to discriminate between various models with equally good description of RHIC data alone.