Solving the $R_{AA}\otimes v_2$ puzzle

TL;DR

This paper demonstrates that incorporating event-by-event viscous hydrodynamics and soft-hard flow correlations into models allows for simultaneous description of high-$p_T$ suppression and elliptic flow, resolving a long-standing puzzle.

Contribution

The study introduces a comprehensive modeling approach combining event-by-event viscous hydrodynamics with energy loss models to accurately predict both soft and hard sector observables.

Findings

Successful simultaneous description of $R_{AA}$ and $v_2$ at high $p_T$

Highlighting the importance of event-by-event fluctuations and flow correlations

Guidance for future differential analyses at LHC run2

Abstract

For the past ten years $R_{AA}(p_T)$, the nuclear modification factor that encodes the suppression of high $p_T$ particles due to energy loss within the medium was fairly well described by many theoretical models. However, the same models systematically under-predicted the high $p_T$ elliptic flow, $v_2$, which is experimentally measured as the correlation between soft and hard hadrons. All previous calculations neglected the effect of event-by-event fluctuations of an expanding viscous hydrodynamical background as well as the soft-hard flow harmonic correlations in the experimentally measured $v_2$. In this talk I show how event-by-event viscous hydrodynamics (computed using the v-USPhydro code) coupled to an energy loss model (BBMG) is able to simultaneously describe soft physics observables as well as the high-$p_T$ $R_{AA}$ and $v_2$. Suggestions for future more differential calculations at the LHC run2 are made to explore soft-hard flow correlations.