Giving wake to energy-energy correlators: Hydrodynamic response on the celestial sphere

TL;DR

This paper develops an analytic model for the hydrodynamic response of quark-gluon plasma to high-energy jets, showing that medium back-reaction influences energy correlators and can explain experimental observations.

Contribution

It provides a novel analytic framework for understanding the medium's hydrodynamic response in energy-energy correlators in heavy-ion collisions.

Findings

Medium response induces a universal classical scaling law.

Large angle correlations can be qualitatively explained by hydrodynamic response.

Hydrodynamic effects compete with perturbative QCD at large angles.

Abstract

The observation of the medium response generated by the propagation of high energy partons in the quark gluon plasma produced in heavy-ion collisions would provide a clear and unmistakable evidence for the hydrodynamic behavior of the bulk. Recently, it has been argued that the features of the medium's back-reaction to the jet could be cleanly imprinted in the correlations of asymptotic energy flows, in principle allowing to isolate this signal from other uncorrelated physical processes. Nonetheless, the current limited theoretical understanding of these jet observables in heavy-ion collisions constrains their applicability as probes of the medium (hydro)dynamics. In this work, we provide an analytic picture for the medium back-reaction's effect on the energy flux and two point energy correlator. We show that the medium response leads to the emergence of an universal classical scaling law, competing with the perturbative QCD contribution at large angles. Comparing the associated correlator to recent experimental measurements, we find that the observed large angle features can be qualitatively described by a purely hydrodynamically driven response and its interplay with the hard jet component.