Observation of Medium-Induced Modifications of Jet Fragmentation in Pb-Pb Collisions at sNN =5.02 TeV Using Isolated Photon-Tagged Jets
PubMed: 30608764 ; 2-s2.0-85059112614 ; 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 pT?>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. © 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 SCOAP3. ; ST/I003622/1, ST/I505580/1, ST/J004871/1, ST/J005479/1, ST/K003542/1, ST/L005603/1, ST/M004775/1, ST/N000242/1 National Science Foundation, NSF National Institutes of Health, NIH U.S. Department of Energy, USDOE Hispanics in Philanthropy, HIP CS Fund, CSF Departamento Administrativo de Ciencia, Tecnología e Innovación (COLCIENCIAS) California Earthquake Authority, CEA Secretaría de Educación Pública, SEP Türkiye Atom Enerjisi Kurumu, TAEK Louisiana Academy of Sciences, LAS Missouri University of Science and Technology, MST CERN College of Arts and Sciences, University of Nebraska-Lincoln, CAS Norwegian Sequencing Centre, NSC Institute for the Promotion of Teaching Science and Technology, IPST Mountain Equipment Co-operative, MEC Science and Technology Facilities Council, STFC: ST/F007434/1, ST/N001273/1 Royal Astronomical Society, RAS Ministry of Education - Singapore, MOE Department of Atomic Energy, Government of India, ???? Science Foundation Ireland, SFI Helmholtz-Gemeinschaft, HGF Deutsche Forschungsgemeinschaft, DFG Fundação de Amparo à Pesquisa do Estado de São Paulo, FAPESP National Natural Science Foundation of China, NSFC Research Promotion Foundation, ???? Fundação para a Ciência e a Tecnologia, FCT Russian Foundation for Basic Research, ???? Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, CAPES Academy of Finland Bundesministerium für Bildung und Forschung, BMBF Austrian Science Fund, FWF Fonds De La Recherche Scientifique - FNRS, FNRS Fonds Wetenschappelijk Onderzoek, FWO Consejo Nacional de Ciencia y Tecnología, CONACYT Bundesministerium für Wissenschaft, Forschung und Wirtschaft, BMWFW General Secretariat for Research and Technology, GSRT Hungarian Scientific Research Fund, OTKA Conselho Nacional de Desenvolvimento Científico e Tecnológico, CNPq Ministry of Science, ICT and Future Planning, MSIP Ministry of Science and Technology, MOST National Research Foundation of Korea, NRF Joint Institute for Nuclear Research, JINR Instituto Nazionale di Fisica Nucleare, INFN National Science and Technology Development Agency, ????: Thailand Secretaría de Educación Superior, Ciencia, Tecnología e Innovación, SENESCYT Universiti Malaya, UM Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro, FAPERJ Ministry for Business Innovation and Employment, MBIE National Academy of Sciences of Ukraine, NASU Ministry of Education and Science, MES Institute for Research in Fundamental Sciences, IPM Benemérita Universidad Autónoma de Puebla, BUAP Secretaría de Estado de Investigación, Desarrollo e Innovación, SEIDI European Regional Development Fund, FEDER Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, CINVESTAV Pakistan Atomic Energy Commission, PAEC State Fund for Fundamental Research of Ukraine, SFFR Department of Science and Technology, Government of West Bengal, DST Federal Agency of Atomic Energy of the Russian Federation ; 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).