https://doi.org/10.1140/epjc/s10052-012-2124-9
Regular Article - Experimental Physics
Transverse sphericity of primary charged particles in minimum bias proton–proton collisions at 
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CERN, 1211, Geneva 23, Switzerland
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Benemérita Universidad Autónoma de Puebla, Puebla, Mexico
3
Bogolyubov Institute for Theoretical Physics, Kiev, Ukraine
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Budker Institute for Nuclear Physics, Novosibirsk, Russia
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California Polytechnic State University, San Luis Obispo, California, United States
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Centre de Calcul de l’IN2P3, Villeurbanne, France
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Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear (CEADEN), Havana, Cuba
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Centro de Investigaciones Energéticas Medioambientales y Tecnológicas (CIEMAT), Madrid, Spain
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Centro de Investigación y de Estudios Avanzados (CINVESTAV), Mexico City and Mérida, Mexico
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Centro Fermi – Centro Studi e Ricerche e Museo Storico della Fisica “Enrico Fermi”, Rome, Italy
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Chicago State University, Chicago, United States
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Commissariat à l’Energie Atomique, IRFU, Saclay, France
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Departamento de Física de Partículas and IGFAE, Universidad de Santiago de Compostela, Santiago de Compostela, Spain
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Department of Physics Aligarh Muslim University, Aligarh, India
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Department of Physics and Technology, University of Bergen, Bergen, Norway
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Department of Physics, Ohio State University, Columbus, Ohio, United States
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Department of Physics, Sejong University, Seoul, South Korea
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Department of Physics, University of Oslo, Oslo, Norway
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Dipartimento di Fisica dell’Università and Sezione INFN, Cagliari, Italy
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Dipartimento di Fisica dell’Università and Sezione INFN, Padova, Italy
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Dipartimento di Fisica dell’Università and Sezione INFN, Trieste, Italy
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Dipartimento di Fisica dell’Università and Sezione INFN, Bologna, Italy
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Dipartimento di Fisica dell’Università ‘La Sapienza’ and Sezione INFN, Rome, Italy
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Dipartimento di Fisica e Astronomia dell’Università and Sezione INFN, Catania, Italy
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Dipartimento di Fisica ‘E.R. Caianiello’ dell’Università and Gruppo Collegato INFN, Salerno, Italy
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Dipartimento di Fisica Sperimentale dell’Università and Sezione INFN, Turin, Italy
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Dipartimento di Scienze e Tecnologie Avanzate dell’Università del Piemonte Orientale and Gruppo Collegato INFN, Alessandria, Italy
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Dipartimento Interateneo di Fisica ‘M. Merlin’ and Sezione INFN, Bari, Italy
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Division of Experimental High Energy Physics, University of Lund, Lund, Sweden
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European Organization for Nuclear Research (CERN), Geneva, Switzerland
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Fachhochschule Köln, Köln, Germany
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Faculty of Engineering, Bergen University College, Bergen, Norway
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Faculty of Mathematics, Physics and Informatics, Comenius University, Bratislava, Slovakia
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Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Prague, Czech Republic
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Faculty of Science, P.J. Šafárik University, Košice, Slovakia
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Frankfurt Institute for Advanced Studies, Johann Wolfgang Goethe-Universität Frankfurt, Frankfurt, Germany
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Gangneung-Wonju National University, Gangneung, South Korea
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Helsinki Institute of Physics (HIP) and University of Jyväskylä, Jyväskylä, Finland
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Hiroshima University, Hiroshima, Japan
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Hua-Zhong Normal University, Wuhan, China
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Indian Institute of Technology, Mumbai, India
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Indian Institute of Technology Indore (IIT), Indore, India
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Institut de Physique Nucléaire d’Orsay (IPNO), Université Paris-Sud, CNRS-IN2P3, Orsay, France
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Institute for High Energy Physics, Protvino, Russia
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Institute for Nuclear Research, Academy of Sciences, Moscow, Russia
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Nikhef, National Institute for Subatomic Physics and Institute for Subatomic Physics of Utrecht University, Utrecht, Netherlands
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Institute for Theoretical and Experimental Physics, Moscow, Russia
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Institute of Experimental Physics, Slovak Academy of Sciences, Košice, Slovakia
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Institute of Physics, Bhubaneswar, India
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Institute of Physics, Academy of Sciences of the Czech Republic, Prague, Czech Republic
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Institute of Space Sciences (ISS), Bucharest, Romania
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Institut für Informatik, Johann Wolfgang Goethe-Universität Frankfurt, Frankfurt, Germany
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Institut für Kernphysik, Johann Wolfgang Goethe-Universität Frankfurt, Frankfurt, Germany
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Institut für Kernphysik, Technische Universität Darmstadt, Darmstadt, Germany
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Institut für Kernphysik, Westfälische Wilhelms-Universität Münster, Münster, Germany
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Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Mexico City, Mexico
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Instituto de Física, Universidad Nacional Autónoma de México, Mexico City, Mexico
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Institut of Theoretical Physics, University of Wroclaw, Wroclaw, Poland
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Institut Pluridisciplinaire Hubert Curien (IPHC), Université de Strasbourg, CNRS-IN2P3, Strasbourg, France
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Joint Institute for Nuclear Research (JINR), Dubna, Russia
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KFKI Research Institute for Particle and Nuclear Physics, Hungarian Academy of Sciences, Budapest, Hungary
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Kirchhoff-Institut für Physik, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany
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Korea Institute of Science and Technology Information, Daejeon, South Korea
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Laboratoire de Physique Corpusculaire (LPC), Clermont Université, Université Blaise Pascal, CNRS–IN2P3, Clermont-Ferrand, France
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Laboratoire de Physique Subatomique et de Cosmologie (LPSC), Université Joseph Fourier, CNRS-IN2P3, Institut Polytechnique de Grenoble, Grenoble, France
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Laboratori Nazionali di Frascati, INFN, Frascati, Italy
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Laboratori Nazionali di Legnaro, INFN, Legnaro, Italy
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Lawrence Berkeley National Laboratory, Berkeley, California, United States
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Lawrence Livermore National Laboratory, Livermore, California, United States
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Moscow Engineering Physics Institute, Moscow, Russia
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National Institute for Physics and Nuclear Engineering, Bucharest, Romania
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Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
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Nikhef, National Institute for Subatomic Physics, Amsterdam, Netherlands
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Nuclear Physics Institute, Academy of Sciences of the Czech Republic, Řež u Prahy, Czech Republic
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Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
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Petersburg Nuclear Physics Institute, Gatchina, Russia
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Physics Department, Creighton University, Omaha, Nebraska, United States
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Physics Department, Panjab University, Chandigarh, India
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Physics Department, University of Athens, Athens, Greece
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Physics Department, University of Cape Town, iThemba LABS, Cape Town, South Africa
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Physics Department, University of Jammu, Jammu, India
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Physics Department, University of Rajasthan, Jaipur, India
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Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany
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Purdue University, West Lafayette, Indiana, United States
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Pusan National University, Pusan, South Korea
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Research Division and ExtreMe Matter Institute EMMI, GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany
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Rudjer Bošković Institute, Zagreb, Croatia
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Russian Federal Nuclear Center (VNIIEF), Sarov, Russia
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Russian Research Centre Kurchatov Institute, Moscow, Russia
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Saha Institute of Nuclear Physics, Kolkata, India
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School of Physics and Astronomy, University of Birmingham, Birmingham, United Kingdom
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Sección Física, Departamento de Ciencias, Pontificia Universidad Católica del Perú, Lima, Peru
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Sezione INFN, Trieste, Italy
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Sezione INFN, Padova, Italy
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Sezione INFN, Turin, Italy
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Sezione INFN, Rome, Italy
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Sezione INFN, Cagliari, Italy
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Sezione INFN, Bologna, Italy
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Sezione INFN, Bari, Italy
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Sezione INFN, Catania, Italy
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Soltan Institute for Nuclear Studies, Warsaw, Poland
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Nuclear Physics Group, STFC Daresbury Laboratory, Daresbury, United Kingdom
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SUBATECH, Ecole des Mines de Nantes, Université de Nantes, CNRS-IN2P3, Nantes, France
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Technical University of Split FESB, Split, Croatia
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The Henryk Niewodniczanski Institute of Nuclear Physics, Polish Academy of Sciences, Cracow, Poland
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Physics Department, The University of Texas at Austin, Austin, TX, United States
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Universidad Autónoma de Sinaloa, Culiacán, Mexico
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Universidade de São Paulo (USP), São Paulo, Brazil
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Universidade Estadual de Campinas (UNICAMP), Campinas, Brazil
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Université de Lyon, Université Lyon 1, CNRS/IN2P3, IPN-Lyon, Villeurbanne, France
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University of Houston, Houston, Texas, United States
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University of Technology and Austrian Academy of Sciences, Vienna, Austria
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University of Tennessee, Knoxville, Tennessee, United States
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University of Tokyo, Tokyo, Japan
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University of Tsukuba, Tsukuba, Japan
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Eberhard Karls Universität Tübingen, Tübingen, Germany
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Variable Energy Cyclotron Centre, Kolkata, India
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V. Fock Institute for Physics, St. Petersburg State University, St. Petersburg, Russia
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Warsaw University of Technology, Warsaw, Poland
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Wayne State University, Detroit, Michigan, United States
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Yale University, New Haven, Connecticut, United States
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Yerevan Physics Institute, Yerevan, Armenia
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Yildiz Technical University, Istanbul, Turkey
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Yonsei University, Seoul, South Korea
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Zentrum für Technologietransfer und Telekommunikation (ZTT), Fachhochschule Worms, Worms, Germany
* e-mail: aortizve@cern.ch
Received:
25
May
2012
Revised:
23
July
2012
Published online:
18
September
2012
Measurements of the sphericity of primary charged particles in minimum bias proton–proton collisions at 
with the ALICE detector at the LHC are presented. The observable is measured in the plane perpendicular to the beam direction using primary charged tracks with p
T>0.5 GeV/c in |η|<0.8. The mean sphericity as a function of the charged particle multiplicity at mid-rapidity (N
ch) is reported for events with different p
T scales (“soft” and “hard”) defined by the transverse momentum of the leading particle. In addition, the mean charged particle transverse momentum versus multiplicity is presented for the different event classes, and the sphericity distributions in bins of multiplicity are presented. The data are compared with calculations of standard Monte Carlo event generators. The transverse sphericity is found to grow with multiplicity at all collision energies, with a steeper rise at low N
ch, whereas the event generators show an opposite tendency. The combined study of the sphericity and the mean p
T with multiplicity indicates that most of the tested event generators produce events with higher multiplicity by generating more back-to-back jets resulting in decreased sphericity (and isotropy). The PYTHIA6 generator with tune PERUGIA-2011 exhibits a noticeable improvement in describing the data, compared to the other tested generators.
© Springer-Verlag Berlin Heidelberg and Società Italiana di Fisica, 2012
