https://doi.org/10.1140/epjc/s10052-009-1227-4
Regular Article - Experimental Physics
First proton–proton collisions at the LHC as observed with the ALICE detector: measurement of the charged-particle pseudorapidity density at
GeV
1
Dipartimento di Scienze e Tecnologie Avanzate dell’Università del Piemonte Orientale and Gruppo Collegato INFN, Alessandria, Italy
2
Department of Physics, Aligarh Muslim University, Aligarh, India
3
National Institute for Nuclear and High Energy Physics (NIKHEF), Amsterdam, The Netherlands
4
Physics Department, University of Athens, Athens, Greece
5
Dipartimento Interateneo di Fisica ‘M. Merlin’ and Sezione INFN, Bari, Italy
6
Sezione INFN, Bari, Italy
7
China Institute of Atomic Energy, Beijing, China
8
Department of Physics and Technology, University of Bergen, Bergen, Norway
9
Faculty of Engineering, Bergen University College, Bergen, Norway
10
Lawrence Berkeley National Laboratory, Berkeley, CA, USA
11
Institute of Physics, Bhubaneswar, India
12
School of Physics and Astronomy, University of Birmingham, Birmingham, UK
13
Dipartimento di Fisica dell’Università and Sezione INFN, Bologna, Italy
14
Sezione INFN, Bologna, Italy
15
Faculty of Mathematics, Physics and Informatics, Comenius University, Bratislava, Slovakia
16
Institute of Space Sciences (ISS), Bucharest, Romania
17
National Institute for Physics and Nuclear Engineering, Bucharest, Romania
18
KFKI Research Institute for Particle and Nuclear Physics, Hungarian Academy of Sciences, Budapest, Hungary
19
Dipartimento di Fisica dell’Università and Sezione INFN, Cagliari, Italy
20
Sezione INFN, Cagliari, Italy
21
Universidade Estadual de Campinas (UNICAMP), Campinas, Brazil
22
Physics Department, University of Cape Town, iThemba Laboratories, Cape Town, South Africa
23
Dipartimento di Fisica e Astronomia dell’Università and Sezione INFN, Catania, Italy
24
Sezione INFN, Catania, Italy
25
Physics Department, Panjab University, Chandigarh, India
26
Laboratoire de Physique Corpusculaire (LPC), Clermont Université, Université Blaise Pascal, CNRS–IN2P3, Clermont-Ferrand, France
27
Department of Physics, Ohio State University, Columbus, OH, USA
28
Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
29
The Henryk Niewodniczanski Institute of Nuclear Physics, Polish Academy of Sciences, Cracow, Poland
30
Physics Department, Creighton University, Omaha, NE, USA
31
Universidad Autónoma de Sinaloa, Culiacán, Mexico
32
ExtreMe Matter Institute EMMI, GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany
33
Institut für Kernphysik, Technische Universität Darmstadt, Darmstadt, Germany
34
Wayne State University, Detroit, MI, USA
35
Joint Institute for Nuclear Research (JINR), Dubna, Russia
36
Frankfurt Institute for Advanced Studies, Johann Wolfgang Goethe-Universität Frankfurt, Frankfurt, Germany
37
Institut für Kernphysik, Johann Wolfgang Goethe-Universität Frankfurt, Frankfurt, Germany
38
Laboratori Nazionali di Frascati, INFN, Frascati, Italy
39
Petersburg Nuclear Physics Institute, Gatchina, Russia
40
European Organization for Nuclear Research (CERN), Geneva, Switzerland
41
Laboratoire de Physique Subatomique et de Cosmologie (LPSC), Université Joseph Fourier, CNRS-IN2P3, Institut Polytechnique de Grenoble, Grenoble, France
42
Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear (CEADEN), Havana, Cuba
43
Kirchhoff-Institut für Physik, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany
44
Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany
45
Hiroshima University, Hiroshima, Japan
46
University of Houston, Houston, TX, USA
47
Physics Department, University of Rajasthan, Jaipur, India
48
Physics Department, University of Jammu, Jammu, India
49
Helsinki Institute of Physics (HIP) and University of Jyväskylä, Jyväskylä, Finland
50
Kangnung National University, Kangnung, South Korea
51
Scientific Research Technological Institute of Instrument Engineering, Kharkov, Ukraine
52
Bogolyubov Institute for Theoretical Physics, Kiev, Ukraine
53
University of Tennessee, Knoxville, TN, USA
54
Saha Institute of Nuclear Physics, Kolkata, India
55
Variable Energy Cyclotron Centre, Kolkata, India
56
Fachhochschule Köln, Köln, Germany
57
Faculty of Science, P.J. Šafárik University, Košice, Slovakia
58
Institute of Experimental Physics, Slovak Academy of Sciences, Košice, Slovakia
59
Laboratori Nazionali di Legnaro, INFN, Legnaro, Italy
60
Lawrence Livermore National Laboratory, Livermore, CA, USA
61
Division of Experimental High Energy Physics, University of Lund, Lund, Sweden
62
Université de Lyon 1, CNRS/IN2P3, Institut de Physique Nucléaire de Lyon, Lyon, France
63
Centro de Investigaciones Energéticas Medioambientales y Tecnológicas (CIEMAT), Madrid, Spain
64
Centro de Investigación y de Estudios Avanzados (CINVESTAV), Mexico City and Mérida, Mexico
65
Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Mexico City, Mexico
66
Instituto de Física, Universidad Nacional Autónoma de México, Mexico City, Mexico
67
Institute for Nuclear Research, Academy of Sciences, Moscow, Russia
68
Institute for Theoretical and Experimental Physics, Moscow, Russia
69
Moscow Engineering Physics Institute, Moscow, Russia
70
Russian Research Centre Kurchatov Institute, Moscow, Russia
71
Indian Institute of Technology, Mumbai, India
72
Institut für Kernphysik, Westfälische Wilhelms-Universität Münster, Münster, Germany
73
SUBATECH, Ecole des Mines de Nantes, Université de Nantes, CNRS-IN2P3, Nantes, France
74
Yale University, New Haven, CT, USA
75
Budker Institute for Nuclear Physics, Novosibirsk, Russia
76
Oak Ridge National Laboratory, Oak Ridge, TN, USA
77
Institut de Physique Nucléaire d’Orsay (IPNO), Université Paris-Sud, CNRS-IN2P3, Orsay, France
78
Department of Physics, University of Oslo, Oslo, Norway
79
Dipartimento di Fisica dell’Università and Sezione INFN, Padova, Italy
80
Sezione INFN, Padova, Italy
81
Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Prague, Czech Republic
82
Institute of Physics, Academy of Sciences of the Czech Republic, Prague, Czech Republic
83
Institute for High Energy Physics, Protvino, Russia
84
Benemérita Universidad Autónoma de Puebla, Puebla, Mexico
85
Pusan National University, Pusan, South Korea
86
Nuclear Physics Institute, Academy of Sciences of the Czech Republic, Řež u Prahy, Czech Republic
87
Dipartimento di Fisica dell’Università ‘La Sapienza’ and Sezione INFN, Rome, Italy
88
Sezione INFN, Rome, Italy
89
Commissariat à l’Energie Atomique, IRFU, Saclay, France
90
Dipartimento di Fisica ‘E.R. Caianiello’ dell’Università and Sezione INFN, Salerno, Italy
91
California Polytechnic State University, San Luis Obispo, CA, USA
92
Departamento de Física de Partículas and IGFAE, Universidad de Santiago de Compostela, Santiago de Compostela, Spain
93
Universidade de São Paulo (USP), São Paulo, Brazil
94
Russian Federal Nuclear Center (VNIIEF), Sarov, Russia
95
Department of Physics, Sejong University, Seoul, South Korea
96
Yonsei University, Seoul, South Korea
97
Technical University of Split FESB, Split, Croatia
98
V. Fock Institute for Physics, St. Petersburg State University, St. Petersburg, Russia
99
Institut Pluridisciplinaire Hubert Curien (IPHC), Université de Strasbourg, CNRS-IN2P3, Strasbourg, France
100
University of Tokyo, Tokyo, Japan
101
Dipartimento di Fisica Sperimentale dell’Università and Sezione INFN, Turin, Italy
102
Sezione INFN, Turin, Italy
103
Dipartimento di Fisica dell’Università and Sezione INFN, Trieste, Italy
104
Sezione INFN, Trieste, Italy
105
University of Tsukuba, Tsukuba, Japan
106
Institute for Subatomic Physics, Utrecht University, Utrecht, The Netherlands
107
Soltan Institute for Nuclear Studies, Warsaw, Poland
108
Warsaw University of Technology, Warsaw, Poland
109
Purdue University, West Lafayette, IN, USA
110
Zentrum für Technologietransfer und Telekommunikation (ZTT), Fachhochschule Worms, Worms, Germany
111
Hua-Zhong Normal University, Wuhan, China
112
Yerevan Physics Institute, Yerevan, Armenia
113
Rudjer Bošković Institute, Zagreb, Croatia
* e-mail: Jurgen.Schukraft@cern.ch
Received:
28
November
2009
Revised:
1
December
2009
Published online:
11
December
2009
On 23rd November 2009, during the early commissioning of the CERN Large Hadron Collider (LHC), two counter-rotating proton bunches were circulated for the first time concurrently in the machine, at the LHC injection energy of 450 GeV per beam. Although the proton intensity was very low, with only one pilot bunch per beam, and no systematic attempt was made to optimize the collision optics, all LHC experiments reported a number of collision candidates. In the ALICE experiment, the collision region was centred very well in both the longitudinal and transverse directions and 284 events were recorded in coincidence with the two passing proton bunches. The events were immediately reconstructed and analyzed both online and offline. We have used these events to measure the pseudorapidity density of charged primary particles in the central region. In the range |η|<0.5, we obtain dN
ch/dη=3.10±0.13(stat.)±0.22(syst.) for all inelastic interactions, and dN
ch/dη=3.51±0.15(stat.)±0.25(syst.) for non-single diffractive interactions. These results are consistent with previous measurements in proton–antiproton interactions at the same centre-of-mass energy at the CERN Sp
S collider. They also illustrate the excellent functioning and rapid progress of the LHC accelerator, and of both the hardware and software of the ALICE experiment, in this early start-up phase.
© Springer-Verlag , 2010