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

TL;DR

This study measures how jet fragmentation differs in lead-lead versus proton-proton collisions at 2.76 TeV, revealing centrality-dependent modifications and enhancements in low-momentum charged particles in central PbPb collisions.

Contribution

It provides the first detailed measurement of jet fragmentation functions in PbPb collisions at this energy, highlighting medium-induced modifications.

Findings

Significant enhancement in low-pt charged particles in central PbPb collisions.

Fragmentation function modifications depend on collision centrality.

Consistent modifications observed across various jet transverse momentum bins.

Abstract

The jet fragmentation function of inclusive jets with transverse momentum pt above 100 GeV in PbPb collisions has been measured using reconstructed charged particles with pt above 1 GeV in a cone of radius 0.3 around the jet axis. A data sample of PbPb collisions collected in 2011 at a nucleon-nucleon center-of-mass energy of sqrt(s[NN]) = 2.76 TeV corresponding to an integrated luminosity of 150 inverse microbarns is used. The results for PbPb collisions as a function of collision centrality and jet transverse momentum are compared to reference distributions based on pp data collected at the same center-of-mass energy in 2013, with an integrated luminosity of 5.3 inverse picobarns. A centrality-dependent modification of the fragmentation function is found. For the most central collisions, a significant enhancement is observed in the PbPb / pp fragmentation function ratio for charged particles with pt less than 3 GeV. This enhancement is observed for all jet pt bins studied.