Evolution of the jet opening angle distribution in holographic plasma

TL;DR

This paper uses holography to study how jet opening angles evolve in strongly coupled plasma, revealing that while individual jets widen, the overall distribution shifts toward smaller angles due to energy loss effects.

Contribution

It introduces a model combining competing effects on jet opening angles in plasma, explaining how the distribution can shift toward smaller angles despite individual broadening.

Findings

Jet distributions shift toward smaller angles in plasma.

Individual jets tend to widen during propagation.

The mean opening angle can decrease even as jets broaden.

Abstract

We use holography to analyze the evolution of an ensemble of jets, with an initial probability distribution for their energy and opening angle as in proton-proton (pp) collisions, as they propagate through an expanding cooling droplet of strongly coupled plasma as in heavy ion collisions. We identify two competing effects: (i) each individual jet widens as it propagates; (ii) the opening angle distribution for jets emerging from the plasma within any specified range of energies has been pushed toward smaller angles, comparing to pp jets with the same energies. The second effect arises because small-angle jets suffer less energy loss and because jets with a higher initial energy are less probable in the ensemble. We illustrate both effects in a simple two-parameter model, and find that their consequence in sum is that the opening angle distribution for jets in any range of energies contains fewer narrow and wide jets. Either effect can dominate in the mean opening angle, for not unreasonable values of the parameters. So, the mean opening angle for jets with a given energy can easily shift toward smaller angles, as experimental data may indicate, even while every jet in the ensemble broadens.