# How Does the Quark-Gluon Plasma Know the Collision Energy?

## TL;DR

This paper investigates how the properties of Quark-Gluon Plasma (QGP) depend on collision energy and magnetic fields, revealing that magnetic effects in peripheral collisions influence plasma characteristics.

## Contribution

It introduces a gauge-gravity model showing magnetic fields in peripheral collisions affect QGP properties, explaining differences observed at different collision energies.

## Key findings

- Magnetic fields in peripheral collisions impact QGP properties.
- Model predicts modifications in jet quenching parameters.
- Magnetic effects can account for differences in plasma behavior.

## Abstract

Heavy ion collisions at the LHC facility generate a Quark-Gluon Plasma (QGP) which, for central collisions, has a higher energy density and temperature than the plasma generated in central collisions at the RHIC. But sufficiently peripheral LHC collisions give rise to plasmas which have the \emph{same} energy density and temperature as the "central" RHIC plasmas. One might assume that the two versions of the QGP would have very similar properties (for example, with regard to jet quenching), but recent investigations have suggested that \emph{they do not}: the plasma "knows" that the overall collision energy is different in the two cases. We argue, using a gauge-gravity analysis, that the strong magnetic fields arising in one case (peripheral collisions), but not the other, may be relevant here. If the residual magnetic field in peripheral LHC plasmas is of the order of at least $eB\,\approx \,5\,m^2_{\pi}$, then the model predicts modifications of the relevant quenching parameter which approach those recently reported.