Multiplicity dependence of light-flavor hadron production in pp collisions at √s = 7 TeV

Abstract

Comprehensive results on the production of unidentified charged particles, π±, K±, K0S, K∗(892)0, p, p̅, ϕ(1020), Λ, Λ̅, Ξ−, Ξ̅+, Ω−, and Ω̅+ hadrons in proton-proton (pp) collisions at √s = 7 TeV at midrapidity (|y|<0.5) as a function of charged-particle multiplicity density are presented. In order to avoid autocorrelation biases, the actual transverse momentum (pT) spectra of the particles under study and the event activity are measured in different rapidity windows. In the highest multiplicity class, the charged-particle density reaches about 3.5 times the value measured in inelastic collisions. While the yield of protons normalized to pions remains approximately constant as a function of multiplicity, the corresponding ratios of strange hadrons to pions show a significant enhancement that increases with increasing strangeness content. Furthermore, all identified particle-to-pion ratios are shown to depend solely on charged-particle multiplicity density, regardless of system type and collision energy. The evolution of the spectral shapes with multiplicity and hadron mass shows patterns that are similar to those observed in p-Pb and Pb-Pb collisions at Large Hadron Collider energies. The obtained pT distributions and yields are compared to expectations from QCD-based pp event generators as well as to predictions from thermal and hydrodynamic models. These comparisons indicate that traces of a collective, equilibrated system are already present in high-multiplicity pp collisions. ; A. I. Alikhanyan National Science Labo- ratory (Yerevan Physics Institute) Foundation (ANSL), State Committee of Science and World Federation of Scientists (WFS), Armenia; Austrian Academy of Sciences and Na- tionalstiftung für Forschung, Technologie und Entwicklung, Austria; Ministry of Communications and High Technologies, National Nuclear Research Center, Azerbaijan; Conselho Na- cional de Desenvolvimento Científico e Tecnológico (CNPq), Universidade Federal do Rio Grande do Sul (UFRGS), Fi- nanciadora de Estudos e Projetos (Finep), and Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), Brazil; Ministry of Science and Technology of China (MSTC), Na- tional Natural Science Foundation of China (NSFC), and Ministry of Education of China (MOEC), China; Ministry of Science and Education, Croatia; Ministry of Education, Youth and Sports of the Czech Republic, Czech Republic; the Danish Council for Independent Research | Natural Sciences, the Carlsberg Foundation, and Danish National Research Foundation (DNRF), Denmark; Helsinki Institute of Physics (HIP), Finland; Commissariat à l'Energie Atomique (CEA), Institut National de Physique Nucléaire et de Physique des Particules (IN2P3), and Centre National de la Recherche Scentifique (CNRS), France; Bundesministerium für Bildung, Wissenschaft, Forschung, und Technologie (BMBF) and GSI Helmholtzzentrum für Schwerionenforschung GmbH, Ger- many; General Secretariat for Research and Technology, Min- istry of Education, Research, and Religions, Greece; National Research, Development, and Innovation Office, Hungary; De- partment of Atomic Energy Government of India (DAE), Department of Science and Technology, Government of India (DST), University Grants Commission, Government of India (UGC), and Council of Scientific and Industrial Research (CSIR), India; Indonesian Institute of Science, Indonesia; Centro Fermi–Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi and Istituto Nazionale di Fisica Nucle- are (INFN), Italy; Institute for Innovative Science and Tech- nology, Nagasaki Institute of Applied Science (IIST), Japan Society for the Promotion of Science (JSPS) KAKENHI, and Japanese Ministry of Education, Culture, Sports, Sci- ence, and Technology (MEXT), Japan; Consejo Nacional de Ciencia (CONACYT) y Tecnología, through Fondo de Coop- eración Internacional en Ciencia y Tecnología (FONCICYT) and Dirección General de Asuntos del Personal Academico (DGAPA), Mexico; Nederlandse Organisatie voor Weten- schappelijk Onderzoek (NWO), Netherlands; the Research Council of Norway, Norway; Commission on Science and Technology for Sustainable Development in the South (COM- SATS), Pakistan; Pontificia Universidad Católica del Perú, Peru; Ministry of Science and Higher Education and National Science Centre, Poland; Korea Institute of Science and Tech- nology Information and National Research Foundation of Ko- rea (NRF), Republic of Korea; Ministry of Education and Sci- entific Research, Institute of Atomic Physics and Romanian National Agency for Science, Technology, and Innovation, Romania; Joint Institute for Nuclear Research (JINR), Min- istry of Education and Science of the Russian Federation and National Research Centre Kurchatov Institute, Russia; Min- istry of Education, Science, Research, and Sport of the Slovak Republic, Slovakia; National Research Foundation of South Africa, South Africa; Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear (CEADEN), Cubaenergía, Cuba, and Cen- tro de Investigaciones Energéticas, Medioambientales y Tec- nológicas (CIEMAT), Spain; Swedish Research Council (VR) and Knut & Alice Wallenberg Foundation (KAW), Sweden; European Organization for Nuclear Research, Switzerland; National Science and Technology Development Agency (NS- DTA), Suranaree University of Technology (SUT), and Office of the Higher Education Commission under NRU project of Thailand, Thailand; Turkish Atomic Energy Agency (TAEK), Turkey; National Academy of Sciences of Ukraine, Ukraine; Science and Technology Facilities Council (STFC), United Kingdom; and National Science Foundation of the United States of America (NSF) and U.S. Department of Energy, Office of Nuclear Physics (DOE NP), USA.