Measurement of transverse momentum relative to dijet systems in PbPb and pp collisions at sqrt(s[NN]) = 2.76 TeV

TL;DR

This paper investigates how energy loss affects jet properties in lead-lead and proton-proton collisions at the LHC by measuring the transverse momentum distribution around dijet systems, revealing medium-induced modifications.

Contribution

It provides the first detailed measurement of transverse momentum relative to dijet systems in PbPb collisions at 2.76 TeV, highlighting medium effects on jet structure.

Findings

PbPb collisions show increased low-pT particle multiplicity at large angles from jets.

Energy imbalance in dijets is compensated by low-pT particles at large angles.

Results indicate significant medium-induced modifications to jet fragmentation.

Abstract

An analysis of dijet events in PbPb and pp collisions is performed to explore the properties of energy loss by partons traveling in a quark-gluon plasma. Data are collected at a nucleon-nucleon center-of-mass energy of 2.76 TeV at the LHC. The distribution of transverse momentum (pT) surrounding dijet systems is measured by selecting charged particles in different ranges of pT and at different angular cones of pseudorapidity and azimuth. The measurement is performed as a function of centrality of the PbPb collisions, the pT asymmetry of the jets in the dijet pair, and the distance parameter R used in the anti-kt jet clustering algorithm. In events with unbalanced dijets, PbPb collisions show an enhanced multiplicity in the hemisphere of the subleading jet, with the pT imbalance compensated by an excess of low-pT particles at large angles from the jet axes.