Abstract
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 p T > 4 GeV/c for dijet events with a leading jet of p T > 100 GeV/c. The fragmentation functions in PbPb events are compared to those in pp data as a function of collision centrality, as well as dijet-p T 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-p T particles is not strongly modified in comparison to that observed for jets in vacuum.
Highlights
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 Compact Muon Solenoid (CMS) detector at the LHC
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
In this Letter, we present a measurement of fragmentation functions in pp and PbPb collisions and a detailed comparison of their shapes measured in the two systems
Summary
The Compact Muon Solenoid (CMS) detector is described in ref. [24]. Only the detector systems used in this analysis are discussed hereafter. The Compact Muon Solenoid (CMS) detector is described in ref. The central part of the CMS detector contains a superconducting solenoid that provides a homogeneous magnetic field of 3.8 T parallel to the beam axis. The ECAL calorimeter is segmented in quasi-projective cells of a granularity in pseudorapidity and azimuthal angle of ∆η × ∆φ = 0.0174 × 0.0174 in the barrel (|η| < 1.5), increasing across the endcap (1.5 < |η| < 3.0) to 0.09 × 0.09 at |η| = 3.0. The CMS trigger system is composed of a first level made of custom hardware processors, which use information from the calorimeters and muon detectors to select events, and the High-Level Trigger (HLT) processor farm, that further decreases the event rate, before data storage
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