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Measurement of the Splitting Function in pp and Pb-Pb Collisions at sNN =5.02 TeV

Research output: Contribution to journalArticle

  • A. M. Sirunyan
  • the CMS Collaboration
Original languageEnglish
Article number142302
Number of pages17
JournalPhysical Review Letters
Issue number14
Early online date3 Mar 2018
DateAccepted/In press - 30 Aug 2017
DateE-pub ahead of print - 3 Mar 2018
DatePublished (current) - 3 Apr 2018


Data from heavy ion collisions suggest that the evolution of a parton shower is modified by interactions with the color charges in the dense partonic medium created in these collisions, but it is not known where in the shower evolution the modifications occur. The momentum ratio of the two leading partons, resolved as subjets, provides information about the parton shower evolution. This substructure observable, known as the splitting function, reflects the process of a parton splitting into two other partons and has been measured for jets with transverse momentum between 140 and 500 GeV, in pp and PbPb collisions at a center-of-mass energy of 5.02 TeV per nucleon pair. In central PbPb collisions, the splitting function indicates a more unbalanced momentum ratio, compared to peripheral PbPb and pp collisions.. The measurements are compared to various predictions from event generators and analytical calculations.

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