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

(CMS Collaboration)

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45 Citations (Scopus)


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.

Original languageEnglish
Article number242301
JournalPhysical Review Letters
Issue number24
Publication statusPublished - 14 Dec 2018

Bibliographical note

Publisher Copyright:
© 2018 CERN, for the CMS Collaboration. Published by the American Physical Society under the terms of the »https://creativecommons.org/licenses/by/4.0/» Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP.


We congratulate our colleagues in the CERN accelerator departments for the excellent performance of the LHC and thank the technical and administrative staffs at CERN and at other CMS institutes for their contributions to the success of the CMS effort. In addition, we gratefully acknowledge the computing centers and personnel of the Worldwide LHC Computing Grid for delivering so effectively the computing infrastructure essential to our analyses. Finally, we acknowledge the enduring support for the construction and operation of the LHC and the CMS detector provided by the following funding agencies: BMWFW and FWF (Austria); FNRS and FWO (Belgium); CNPq, CAPES, FAPERJ, and FAPESP (Brazil); MES (Bulgaria); CERN; CAS, MoST, and NSFC (China); COLCIENCIAS (Colombia); MSES and CSF (Croatia); RPF (Cyprus); SENESCYT (Ecuador); MoER, ERC IUT, and ERDF (Estonia); Academy of Finland, MEC, and HIP (Finland); CEA and CNRS/IN2P3 (France); BMBF, DFG, and HGF (Germany); GSRT (Greece); OTKA and NIH (Hungary); DAE and DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); MSIP and NRF (Republic of Korea); LAS (Lithuania); MOE and UM (Malaysia); BUAP, CINVESTAV, CONACYT, LNS, SEP, and UASLP-FAI (Mexico); MBIE (New Zealand); PAEC (Pakistan); MSHE and NSC (Poland); FCT (Portugal); JINR (Dubna); MON, Federal Agency of Atomic Energy of the Russian FederationRosAtom, RAS, RFBR and RAEP (Russia); MESTD (Serbia); SEIDI, CPAN, PCTI and FEDER (Spain); Swiss Funding Agencies (Switzerland); MST (Taipei); ThEPCenter, IPST, STAR, and NSTDA (Thailand); TUBITAK and TAEK (Turkey); NASU and SFFR (Ukraine); STFC (United Kingdom); DOE and NSF (USA).

FundersFunder number
Not addedST/I505580/1, ST/K003542/1, ST/M004775/1, ST/L005603/1, ST/J004871/1, ST/I003622/1, ST/J005479/1, ST/N000242/1
Swiss Funding Agencies
National Science Foundation
National Institutes of Health
U.S. Department of Energy
Hispanics in Philanthropy
CS Fund
Departamento Administrativo de Ciencia, Tecnología e Innovación (COLCIENCIAS)
California Earthquake Authority
Secretaría de Educación Pública
Türkiye Atom Enerjisi Kurumu
Louisiana Academy of Sciences
Missouri University of Science and Technology
College of Arts and Sciences, University of Nebraska-Lincoln
Norwegian Sequencing Centre
Institute for the Promotion of Teaching Science and Technology
Mountain Equipment Co-operative
Science and Technology Facilities CouncilST/F007434/1, GRIDPP, ST/N001273/1
Royal Astronomical Society
Ministry of Education - Singapore
Department of Atomic Energy, Government of India
Science Foundation Ireland
Deutsche Forschungsgemeinschaft
Fundação de Amparo à Pesquisa do Estado de São Paulo
National Natural Science Foundation of China
Research Promotion Foundation
Fundação para a Ciência e a Tecnologia
Russian Foundation for Basic Research
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Academy of Finland
Bundesministerium für Bildung und Forschung
Austrian Science Fund
Fonds De La Recherche Scientifique - FNRS
Fonds Wetenschappelijk Onderzoek
Consejo Nacional de Ciencia y Tecnología
Bundesministerium für Wissenschaft, Forschung und Wirtschaft
General Secretariat for Research and Technology
Hungarian Scientific Research Fund
Conselho Nacional de Desenvolvimento Científico e Tecnológico
Ministry of Science, ICT and Future Planning
Ministry of Science and Technology
National Research Foundation of Korea
Joint Institute for Nuclear Research
Instituto Nazionale di Fisica Nucleare
National Science and Technology Development AgencyThailand
Secretaría de Educación Superior, Ciencia, Tecnología e Innovación
Universiti Malaya
Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro
Ministry for Business Innovation and Employment
National Academy of Sciences of Ukraine
Ministry of Education and Science
Institute for Research in Fundamental Sciences
Benemérita Universidad Autónoma de Puebla
Secretaría de Estado de Investigación, Desarrollo e Innovación
European Regional Development Fund
Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional
Pakistan Atomic Energy Commission
State Fund for Fundamental Research of Ukraine
Department of Science and Technology, Government of West Bengal
Federal Agency of Atomic Energy of the Russian Federation


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