Jet shapes of isolated photon-tagged jets in PbPb and pp collisions at $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV

TL;DR

This study investigates how jet shapes associated with isolated photons differ between PbPb and pp collisions at 5.02 TeV, revealing medium-induced modifications in central heavy ion collisions.

Contribution

It provides the first detailed comparison of photon-tagged jet shapes in PbPb and pp collisions at this energy, highlighting medium effects on jet structure.

Findings

Jet shapes are similar in peripheral PbPb and pp collisions.

Central PbPb collisions show broader jet shapes with more momentum at larger radii.

Medium interactions cause jet broadening in central heavy ion collisions.

Abstract

The modification of jet shapes in PbPb collisions, relative to those in pp collisions, is studied for jets associated with an isolated photon. The data were collected with the CMS detector at the LHC at a nucleon-nucleon center-of-mass energy of 5.02 TeV. Jet shapes are constructed from charged particles with track transverse momenta ($p_\mathrm{T}$) above 1 GeV/c in annuli around the axes of jets with $p^\mathrm{jet}_\mathrm{T}$ $>$ 30 GeV/c associated with an isolated photon with $p^\gamma_\mathrm{T}$ $>$ 60 GeV/c. The jet shape distributions are consistent between peripheral PbPb and pp collisions, but are modified for more central PbPb collisions. In these central PbPb events, a larger fraction of the jet momentum is observed at larger distances from the jet axis compared to pp, reflecting the interaction between the partonic medium created in heavy ion collisions and the traversing partons.