Event-by-event fluctuations in the medium-induced jet evolution

TL;DR

This paper models the stochastic process of medium-induced gluon branching in jets propagating through dense QCD media, revealing large event-by-event fluctuations and scaling laws in soft gluon production and energy loss.

Contribution

It introduces an event-by-event framework for gluon distribution in medium-induced jet evolution, highlighting large fluctuations and KNO scaling in multiplicity distributions.

Findings

Large fluctuations in energy loss and soft gluon multiplicity.

Existence of KNO scaling in medium-induced gluon distributions.

Predictions of significant event-by-event fluctuations in Pb+Pb collisions at LHC.

Abstract

We develop the event-by-event picture of the gluon distribution produced via medium-induced gluon branching by an energetic jet which propagates through a dense QCD medium. A typical event is characterized by the production of a large number of soft gluons which propagate at large angles with respect to the jet axis and which collectively carry a substantial amount of energy. By explicitly computing 2-gluon correlations, we demonstrate the existence of large event-by-event fluctuations, which reflect the stochastic nature of the branching process. For the two quantities that we have investigated -- the energy loss at large angles and the soft gluon multiplicity --, the dispersion is parametrically as large as the respective expectation value. We identify interesting scaling laws, which suggest that the multiplicity distribution should exhibit KNO (Koba-Nielsen-Olesen) scaling. A similar scaling is known to hold for a jet branching in the vacuum, but the medium-induced distribution is found to be considerably broader. We predict that event-by-event measurements of the di-jet asymmetry in Pb+Pb collisions at the LHC should observe large fluctuations in the number of soft hadrons propagating at large angles and also in the total energy carried by these hadrons.