Observation of Medium-Induced Modifications of Jet Fragmentation in Pb-Pb Collisions at √s[subscript NN] = 5.02 TeV Using Isolated Photon-Tagged Jets
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PhysRevLett.121.242301.pdf
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Author(s)
CMS Collaboration
Abercrombie, Daniel Robert
Allen, Brandon Leigh
Azzolini, Virginia
Barbieri, Richard Alexander
Baty, Austin Alan
Bauer, Gerry P
Bi, Ran
Brandt, Stephanie Akemi
Busza, Wit
Date Issued
December 2018
Journal
Physical Review Letters
Publisher
American Physical Society
Citation
Sirunyan, A. M. et al. “Observation of Medium-Induced Modifications of Jet Fragmentation in Pb-Pb Collisions at √s[subscript NN] = 5.02 TeV
Using Isolated Photon-Tagged Jets.” Physical Review Letters 121, 24 (December 2018) © 2018 CERN, for the CMS Collaboration
Version
Final published version
Abstract
Measurements of fragmentation functions for jets associated with an isolated photon are presented for the first time in pp and Pb-Pb collisions. The analysis uses data collected with the CMS detector at the CERN LHC at a nucleon-nucleon center-of-mass energy of 5.02 TeV. Fragmentation functions are obtained for jets with pTjet>30 GeV/c in events containing an isolated photon with pTγ>60 GeV/c, using charged tracks with transverse momentum pTtrk>1 GeV/c in a cone around the jet axis. The association with an isolated photon constrains the initial pT and azimuthal angle of the parton whose shower produced the jet. For central Pb-Pb collisions, modifications of the jet fragmentation functions are observed when compared to those measured in pp collisions, while no significant differences are found in the 50% most peripheral collisions. Jets in central Pb-Pb events show an excess (depletion) of low (high) pT particles, with a transition around 3 GeV/c. This measurement shows for the first time the in-medium shower modifications of partons (quark dominated) with well-defined initial kinematics. It constitutes a new well-controlled reference for testing theoretical models of the parton passage through the quark-gluon plasma.
MIT Department
Massachusetts Institute of Technology. Department of Nuclear Science and Engineering
Massachusetts Institute of Technology. Department of Physics
Massachusetts Institute of Technology. Laboratory for Nuclear Science
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DOI of Published Version
https://doi.org/10.1103/PhysRevLett.121.242301
