Observation of the jet diffusion wake using dijets in heavy ion collisions

TL;DR

This paper presents the first clear experimental evidence of jet diffusion wakes in heavy ion collisions, showing how jets modify the surrounding medium and revealing properties of the quark-gluon plasma.

Contribution

It provides the first measurement of the jet diffusion wake in heavy ion collisions, comparing dijet-hadron correlations in PbPb and pp collisions at 5.02 TeV.

Findings

Jet diffusion wake observed with >5 sigma significance for 1-2 GeV particles.

Differences in dijet-hadron correlations indicate medium response to jets.

Model comparisons shed light on quark-gluon plasma properties.

Abstract

Energetic quarks and gluons traversing a hot and dense quark-gluon plasma deposit energy and momentum into the medium before hadronizing to collimated sprays of particles, known as jets. This energy-momentum deposition is expected to produce medium responses, collectively known as jet wakes, with ``diffusion wake'' denoting a depletion of particles in the direction opposite to the propagating jet. These phenomena are studied by comparing dijet-hadron correlations measured in lead-lead (PbPb) and proton-proton (pp) collisions to assess jet-induced modifications of bulk particle production. The analysis uses PbPb and pp data recorded at a nucleon-nucleon center-of-mass energy $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV with the CMS detector at the CERN LHC. By exploring how the dijet-hadron correlation distributions differ for various pseudorapidity separations of the two jets in the dijet, the presence of a jet diffusion wake is firmly established. The wake has a significance greater than 5 standard deviations for charged particles in the transverse momentum range 1 $\lt$ $p_\mathrm{T}$ $\lt$ 2 GeV. The measurements are compared with various model predictions with and without jet wake effects, providing new insights into quark-gluon plasma properties and the formation of jet-induced wakes.