Measurement of jet fragmentation into charged particles in pp and PbPb collisions at sqrt(s[NN]) = 2.76 TeV

TL;DR

This study compares jet fragmentation in proton-proton and lead-lead collisions at 2.76 TeV, revealing that high-pt particle distribution within jets remains largely unchanged despite significant parton energy loss in PbPb collisions.

Contribution

It provides the first detailed comparison of jet fragmentation functions in PbPb and pp collisions at the LHC energy, highlighting minimal modification in fragmentation patterns.

Findings

Fragmentation functions are similar in PbPb and pp collisions.

No significant modification in high-pt particle distribution within jets.

Evidence of energy loss without altering fragmentation pattern.

Abstract

Jet fragmentation in pp and PbPb collisions at a centre-of-mass energy of 2.76 TeV per nucleon pair was studied using data collected with the CMS detector at the LHC. Fragmentation functions are constructed using charged-particle tracks with transverse momenta pt > 4 GeV for dijet events with a leading jet of pt > 100 GeV. The fragmentation functions in PbPb events are compared to those in pp data as a function of collision centrality, as well as dijet-pt imbalance. Special emphasis is placed on the most central PbPb events including dijets with unbalanced momentum, indicative of energy loss of the hard scattered parent partons. The fragmentation patterns for both the leading and subleading jets in PbPb collisions agree with those seen in pp data at 2.76 TeV. The results provide evidence that, despite the large parton energy loss observed in PbPb collisions, the partition of the remaining momentum within the jet cone into high-pt particles is not strongly modified in comparison to that observed for jets in vacuum.