Measurement of inclusive jet charged-particle fragmentation functions in Pb+Pb collisions at √s_NN = 2.76 TeV with the ATLAS detector

Abstract

Measurements of charged-particle fragmentation functions of jets produced in ultra-relativistic nuclear collisions can provide insight into the modification of parton showers in the hot, dense medium created in the collisions. ATLAS has measured jets in √s_NN = 2.76 TeV Pb+Pb collisions at the LHC using a data set recorded in 2011 with an integrated luminosity of 0.14 nb⁻¹. Jets were reconstructed using the anti-kt algorithm with distance parameter values R = 0.2, 0.3, and 0.4. Distributions of charged-particle transverse momentum and longitudinal momentum fraction are reported for seven bins in collision centrality for R = 0.4 jets with p^jet_T > 100 GeV. Commensurate minimum p_T values are used for the other radii. Ratios of fragment distributions in each centrality bin to those measured in the most peripheral bin are presented. These ratios show a reduction of fragment yield in central collisions relative to peripheral collisions at intermediate z values, 0.04 ≲ z ≲ 0.2, and an enhancement in fragment yield for z ≲ 0.04. A smaller, less significant enhancement is observed at large z and large p_T in central collisions.