Medium-Induced QCD Cascade: Democratic Branching and Wave Turbulence

TL;DR

This paper investigates how medium-induced gluon cascades in quark-gluon plasma exhibit democratic branching and wave turbulence, facilitating energy transport and explaining soft quanta excess in heavy-ion collisions.

Contribution

It introduces the concept of quasidemocratic branchings and wave turbulence in medium-induced QCD cascades, highlighting their role in energy transport in quark-gluon plasma.

Findings

Medium-induced branchings are quasidemocratic, with offspring carrying large energy fractions.

The cascade exhibits wave turbulence with a $1/\sqrt{\omega}$ spectrum.

Turbulent flow may explain excess soft energy in Pb-Pb collision dijet asymmetry.

Abstract

We study the average properties of the gluon cascade generated by an energetic parton propagating through a quark-gluon plasma. We focus on the soft, medium-induced emissions which control the energy transport at large angles with respect to the leading parton. We show that the effect of multiple branchings is important. In contrast with what happens in a usual QCD cascade in vacuum, medium-induced branchings are quasidemocratic, with offspring gluons carrying sizable fractions of the energy of their parent gluon. This results in an efficient mechanism for the transport of energy toward the medium, which is akin to wave turbulence with a scaling spectrum $\sim 1/\sqrt{\omega}$. We argue that the turbulent flow may be responsible for the excess energy carried by very soft quanta, as revealed by the analysis of the dijet asymmetry observed in Pb-Pb collisions at the LHC.