Abstract
The first measurement of jet shapes, defined as the fractional transverse momentum radial distribution, for inclusive jets produced in heavy-ion collisions is presented. Data samples of PbPb and pp collisions, corresponding to integrated luminosities of 150 μb−1 and 5.3 pb−1 respectively, were collected at a nucleon–nucleon centre-of-mass energy of sNN=2.76 TeV with the CMS detector at the LHC. The jets are reconstructed with the anti-kT algorithm with a distance parameter R=0.3, and the jet shapes are measured for charged particles with transverse momentum pT>1 GeV/c. The jet shapes measured in PbPb collisions in different collision centralities are compared to reference distributions based on the pp data. A centrality-dependent modification of the jet shapes is observed in the more central PbPb collisions, indicating a redistribution of the energy inside the jet cone. This measurement provides information about the parton shower mechanism in the hot and dense medium produced in heavy-ion collisions.
Highlights
High transverse momentum partons produced in heavy-ion collisions are expected to lose energy while traversing the hot and dense medium created in these collisions [1,2]
With the order of magnitude increase in the centre-of-mass energy compared to Relativistic Heavy Ion Collider (RHIC), jets with energies well above the background from the underlying event are observed at the Large Hadron Collider (LHC)
To further elucidate the multi-gluon emission process and the in-medium shower development [26,27,28,29,30,31,32], we study the inclusive jet transverse-momentum profiles in PbPb collisions of different centralities including low-pT particles (>1 GeV/c), and perform a direct comparison with the jet shapes measured in pp collisions
Summary
High transverse momentum partons produced in heavy-ion collisions are expected to lose energy while traversing the hot and dense medium created in these collisions [1,2]. The jet shape measurements are performed using charged particles that are reconstructed by the CMS tracking system, located inside the calorimeter and the superconducting coil It consists of silicon pixel and strip layers covering the pseudorapidity range |η| < 2.5 and provides track reconstruction with momentum resolution of about 1–2% up to pT = 100 GeV/c. The events selected for this analysis in PbPb collisions are using an inclusive single-jet trigger which requires an L1 jet with pT > 52 GeV/c and an HLT jet with pT > 80 GeV/c, where the jets are reconstructed using the energy deposits in the calorimeters. Further details on the triggering and event selections can be found in Ref. [23]
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