Jet quenching as a probe of the initial stages in heavy-ion collisions

Carlota Andres,Néstor Armesto,Harri Niemi,Risto Paatelainen,Carlos A Salgado

doi:10.1016/j.physletb.2020.135318

Abstract

Jet quenching provides a very flexible variety of observables which are sensitive to different energy- and time-scales of the strongly interacting matter created in heavy-ion collisions. Exploiting this versatility would make jet quenching an excellent chronometer of the yoctosecond structure of the evolution process. Here we show, for the first time, that a combination of jet quenching observables is sensitive to the initial stages of heavy-ion collisions, when the approach to local thermal equilibrium is expected to happen. Specifically, we find that in order to reproduce at the same time the inclusive particle production suppression, RAA, and the high-pT azimuthal asymmetries, v2, energy loss must be strongly suppressed for the first ∼0.6 fm. This exploratory analysis shows the potential of jet observables, possibly more sophisticated than the ones studied here, to constrain the dynamics of the initial stages of the evolution.

Highlights

Jet quenching provides a very flexible variety of observables which are sensitive to different energy- and time-scales of the strongly interacting matter created in heavy-ion collisions
We restrict our study of the nuclear modification factor and the high-p T harmonics to one center of mass energy and one cen√
We have analyzed the dependence of these observables on the fragmentation functions (FFs), on the lack - or not - of energy loss in the hadronic phase of the evolution, and on the starting time of the quenching

Summary

Introduction

Heavy-ion collisions are the experimental tools designed to study the properties of the hot and dense Quark Gluon Plasma (QGP). The experimental data on v 2 at high-p T can only be described by delaying the beginning of the energy loss for ∼ 0.6 fm This general conclusion that we draw here for the first time is not limited to our specific implementation, since all studies that describe the jet harmonic coefficients start the energy loss and hydrodynamical evolution at the same time [33,41,42,43,44], implicitly implementing this time delay. R A A and v n but rather to show the importance of the initial stages of the evolution for their correct interpretation It would be tempting, on the other hand, to relate our findings to the absence of jet quenching in p-Pb collisions.

The formalism

Results

Conclusions