Observation of Medium-Induced Modifications of Jet Fragmentation in Pb-Pb Collisions at √<i>s</i><sub>NN</sub>=5.02 TeV Using Isolated Photon-Tagged Jets



Sirunyan, AM, Tumasyan, A, Adam, W, Ambrogi, F, Asilar, E, Bergauer, T, Brandstetter, J, Brondolin, E, Dragicevic, M, Eroe, J
et al (show 2249 more authors) (2018) Observation of Medium-Induced Modifications of Jet Fragmentation in Pb-Pb Collisions at √<i>s</i><sub>NN</sub>=5.02 TeV Using Isolated Photon-Tagged Jets. PHYSICAL REVIEW LETTERS, 121 (24). 242301-.

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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 p_{T}^{jet}>30  GeV/c in events containing an isolated photon with p_{T}^{γ}>60  GeV/c, using charged tracks with transverse momentum p_{T}^{trk}>1  GeV/c in a cone around the jet axis. The association with an isolated photon constrains the initial p_{T} 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) p_{T} 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.

Item Type: Article
Uncontrolled Keywords: CMS Collaboration
Depositing User: Symplectic Admin
Date Deposited: 22 Feb 2019 14:45
Last Modified: 13 Oct 2023 14:08
DOI: 10.1103/PhysRevLett.121.242301
Open Access URL: https://doi.org/10.1103/PhysRevLett.121.242301
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URI: https://livrepository.liverpool.ac.uk/id/eprint/3033277