Jet quenching in strongly coupled plasma

TL;DR

This paper models how energetic light quarks lose energy passing through a strongly coupled plasma, revealing that the resulting jets resemble vacuum jets with larger opening angles, and provides a geometric characterization of energy loss.

Contribution

It introduces a geometric framework for understanding energy loss of light quarks in strongly coupled plasma and derives a specific relation for energy loss dependence on slab thickness.

Findings

Jets retain vacuum-like structure after energy loss.

The opening angle of jets increases after passing through plasma.

Energy loss scales with the square of the slab thickness.

Abstract

We present calculations in which an energetic light quark shoots through a finite slab of strongly coupled ${\cal N}=4$ supersymmetric Yang-Mills (SYM) plasma, with thickness $L$, focussing on what comes out on the other side. We find that even when the "jets" that emerge from the plasma have lost a substantial fraction of their energy they look in almost all respects like "jets" in vacuum with the same reduced energy. The one possible exception is that the opening angle of the "jet" is larger after passage through the slab of plasma than before. Along the way, we obtain a fully geometric characterization of energy loss in the strongly coupled plasma and show that $dE_{\rm out}/dL \propto L^2/\sqrt{x^2_{\rm stop}-L^2}$, where $E_{\rm out}$ is the energy of the "jet" that emerges from the slab of plasma and $x_{\rm stop}$ is the (previously known) stopping distance for the light quark in an infinite volume of plasma.