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Observation of Medium-Induced Modifications of Jet Fragmentation in Pb-Pb Collisions at sNN =5.02 TeV Using Isolated Photon-Tagged Jets

par Beghin, Diego ;Bilin, Bugra ;Brun, Hugues ;Clerbaux, Barbara ;De Lentdecker, Gilles ;Delannoy, Hugo ;Dorney, Brian ;Fasanella, Giuseppe ;Favart, Laurent ;Goldouzian, Reza ;Grebenyuk, Anastasia ;Kalsi, Amandeep Kaur ;Lenzi, Thomas ;Luetic, Jelena ;Maerschalk, Thierry ;Marinov, Audrey ;Seva, Tomislav ;Starling, Elizabeth Rose ;Vander Velde, Catherine ;Vanlaer, Pascal ;Vannerom, David ;Yonamine, Ryo ;Zenoni, Florian ; [et al.]
Référence Physical review letters, 121, 242301
Publication Publié, 2018-12-14

Article révisé par les pairs

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Résumé :

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.