Study of the solar anisotropy of cosmic ray primaries of about 200 GeV energy with the L3+C muon detector

¹ III. Physikalisches Institut, RWTH, 52056 Aachen, Germany NIKHEF, and University of Amsterdam, 1009 DB Amsterdam, The Netherlands University of Michigan, Ann Arbor, MI 48109, USA LAPP, IN2P3-CNRS, BP 110, 74941 Annecy-le-Vieux Cedex, France Institute of Physics, University of Basel, 4056 Basel, Switzerland Louisiana State University, Baton Rouge, LA 70803, USA Institute of High Energy Physics, IHEP, 100039 Beijing, PR China ITP, Academia Sinica, 100039 Beijing, PR China Humboldt University, 10115 Berlin, Germany University of Bologna and INFN-Sezione di Bologna, 40126 Bologna, Italy Tata Institute of Fundamental Research, Mumbai (Bombay) 400 005, India Northeastern University, Boston, MA 02115, USA Institute of Atomic Physics and University of Bucharest, 76900 Bucharest, Romania Central Research Institute for Physics of the Hungarian Academy of Sciences, 1525 Budapest 114, Hungary Massachusetts Institute of Technology, Cambridge, MA 02139, USA Panjab University, Chandigarh 160 014, India KLTE-ATOMKI, 4010 Debrecen, Hungary UCD School of Physics, University College Dublin, Belfield, Dublin 4, Ireland University of Florence and INFN, Sezione di Firenze, 50019 Sesto Fiorentino, Italy European Laboratory for Particle Physics, CERN, 1211 Geneva 23, Switzerland World Laboratory, FBLJA Project, 1211 Geneva 23, Switzerland University of Geneva, 1211 Geneva 4, Switzerland University of Hamburg, 22761 Hamburg, Germany Chinese University of Science and Technology, USTC, Hefei, Anhui 230 029, PR China University of Lausanne, 1015 Lausanne, Switzerland Institut de Physique Nucléaire de Lyon, IN2P3-CNRS, Université Claude Bernard, 69622 Villeurbanne, France Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, CIEMAT, 28040 Madrid, Spain Florida Institute of Technology, Melbourne, FL 32901, USA INFN-Sezione di Milano, 20133 Milan, Italy Institute of Theoretical and Experimental Physics, ITEP, Moscow, Russia INFN-Sezione di Napoli and University of Naples, 80125 Naples, Italy Department of Physics, University of Cyprus, Nicosia, Cyprus Radboud University and NIKHEF, 6525 ED Nijmegen, The Netherlands Osaka City University, Osaka 558-8585, Japan California Institute of Technology, Pasadena, CA 91125, USA INFN-Sezione di Perugia and Università Degli Studi di Perugia, 06100 Perugia, Italy Nuclear Physics Institute, St. Petersburg, Russia Carnegie Mellon University, Pittsburgh, PA 15213, USA INFN-Sezione di Napoli and University of Potenza, 85100 Potenza, Italy Princeton University, Princeton, NJ 08544, USA University of California, Riverside, CA 92521, USA INFN-Sezione di Roma and University of Rome, “La Sapienza”, 00185 Rome, Italy University and INFN, Salerno, 84100 Salerno, Italy University of California, San Diego, CA 92093, USA University of Santiago de Compostela, 15706 Santiago, Spain Bulgarian Academy of Sciences, Central Lab. of Mechatronics and Instrumentation, 1113 Sofia, Bulgaria The Center for High Energy Physics, Kyungpook National University, 702-701 Taegu, Republic of Korea National Central University, Chung-Li, Taiwan, China Department of Physics, National Tsing Hua University, Taiwan, China Purdue University, West Lafayette, IN 47907, USA Paul Scherrer Institut, PSI, 5232 Villigen, Switzerland
DESY, 15738 Zeuthen, Germany Eidgenössische Technische Hochschule, ETH Zürich, 8093 Zürich, Switzerland e-mail: Pierre.Le.Coultre@cern.ch Supported by the German Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie Supported by the Hungarian OTKA fund under contract numbers T019181, F023259 and T037350 Also supported by the Hungarian OTKA fund under contract number T026178 Supported also by the Comisión Interministerial de Ciencia y Tecnología Also supported by CONICET and Universidad Nacional de La Plata, CC 67, 1900 La Plata, Argentina Supported by the National Natural Science Foundation of China On leave from the Moscow Physical Engineering Institute (MePhl) On leave from JINR, 141980 Dubna, Russia Deceased

Received: 22 February 2008
Accepted: 3 June 2008

Abstract

Context. Primary cosmic rays experience multiple deflections in the non-uniform galactic and heliospheric magnetic fields which may generate anisotropies.

Aims. A study of anisotropies in the energy range between 100 and 500 GeV is performed. This energy range is not yet well explored.

Methods. The L3 detector at the CERN electron-positron collider, LEP, is used for a study of the angular distribution of atmospheric muons with energies above 20 GeV. This distribution is used to investigate the isotropy of the time-dependent intensity of the primary cosmic-ray flux with a Fourier analysis.

Results. A small deviation from isotropy at energies around 200 GeV is observed for the second harmonics at the solar frequency. No sidereal anisotropy is found at a level above 10^-4. The measurements were performed in the years 1999 and 2000.