Observation and studies of jet quenching in PbPb collisions at nucleon-nucleon center-of-mass energy = 2.76 TeV

TL;DR

This study observes jet quenching in PbPb collisions at 2.76 TeV, showing increased dijet momentum imbalance with collision centrality and softening of jet fragmentation, indicating energy loss in the quark-gluon plasma.

Contribution

First detailed measurement of jet quenching effects in PbPb collisions at 2.76 TeV using CMS detector data, revealing momentum imbalance and fragmentation modifications.

Findings

Dijet momentum imbalance increases with collision centrality.

Softening of jet fragmentation pattern observed.

Momentum balance recovered with low transverse momentum particles.

Abstract

Jet production in PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV was studied with the CMS detector at the LHC, using a data sample corresponding to an integrated luminosity of 6.7 inverse microbarns. Jets are reconstructed using the energy deposited in the CMS calorimeters and studied as a function of collision centrality. With increasing collision centrality, a striking imbalance in dijet transverse momentum is observed, consistent with jet quenching. The observed effect extends from the lower cut-off used in this study (jet transverse momentum = 120 GeV/c) up to the statistical limit of the available data sample (jet transverse momentum approximately 210 GeV/c). Correlations of charged particle tracks with jets indicate that the momentum imbalance is accompanied by a softening of the fragmentation pattern of the second most energetic, away-side jet. The dijet momentum balance is recovered when integrating low transverse momentum particles distributed over a wide angular range relative to the direction of the away-side jet.