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Astron. Astrophys. 359, 682-694 (2000)


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Energy spectrum and chemical composition of cosmic rays between 0.3 and 10 PeV determined from the Cherenkov-light and charged-particle distributions in air showers

The HEGRA-Collaboration
F. Arqueros 3, J.A. Barrio 2,3, K. Bernlöhr *  1, H. Bojahr 6, I. Calle 3, J.L. Contreras 3, J. Cortina 3,2, T. Deckers 5, S. Denninghoff 2, V. Fonseca 3, J. Gebauer 2, J.C. González 3, V. Haustein **  4, G. Heinzelmann 4, H. Hohl 6, D. Horns 4, A. Ibarra 3, M. Kestel 2, O. Kirstein 5, H. Kornmayer 2, D. Kranich 2, H. Krawczynski 1,4, A. Lindner 4, E. Lorenz 2, N. Magnussen 6, H. Meyer 6, R. Mirzoyan 2, A. Moralejo 3, L. Padilla 3, D. Petry ***  2,6, R. Plaga 2, J. Prahl 4, G. Rauterberg 5, W. Rhode 6, A. Röhring 4, M. Samorski 5, D. Schmele 4, F. Schröder 6, W. Stamm 5, B. Wiebel-Sooth 6, M. Willmer 5 and W. Wittek 2


1 Max-Planck-Institut für Kernphysik, Postfach 103980, 69029 Heidelberg, Germany
2 Max-Planck-Institut für Physik, Föhringer Ring 6, 80805 München, Germany
3 Universidad Complutense, Facultad de Ciencias Físicas, Ciudad Universitaria, 28040 Madrid, Spain
4 Universität Hamburg, II. Institut für Experimentalphysik, Luruper Chaussee 149, 22761 Hamburg, Germany
5 Universität Kiel, Institut für Experimentelle und Angewandte Physik, Leibnizstrasse 15, 24118 Kiel, Germany
6 Universität Wuppertal, Fachbereich Physik, Gaussstrasse 20, 42097 Wuppertal, Germany

Received 6 April 1999 / Accepted 17 August 1999

Abstract

Measurements of the lateral distribution of Cherenkov photons with the wide-angle atmospheric Cherenkov light detector array AIROBICC and of the charged particle lateral distribution with the scintillator matrix of the HEGRA air-shower detector complex in air showers are reported. They are used in conjunction to determine the energy spectrum and coarse chemical composition of charged cosmic rays in the energy interval from 0.3 PeV to 10 PeV. With the atmospheric shower-front sampling technique these detectors measure the electromagnetic component of an extensive air shower via the lateral density distribution of the shower particles and of the Cherenkov photons. The data are compared with events generated with the CORSIKA program package with the QGSJET hadronic-event generator. Consistency checks performed with primary energy-reconstruction methods based on different shower observables indicate satisfactory agreement between these extensive air shower simulations and the experimental data. This permits to derive results concerning the energy spectrum and composition of charged cosmic rays.

The energy spectrum features a so called "knee" at an energy of [FORMULA]=[FORMULA] PeV. Power law fits to the differential energy spectrum yield indices of [FORMULA] below and [FORMULA] above the knee.

The best-fit elongation rate for the whole energy range is determined to 78.3 [FORMULA] 1.0 (stat) [FORMULA] 6.2 (syst) g/cm2. At the highest energies it seems to decrease slightly. The best-fit fraction of light nuclei decreases from [FORMULA] (combined statistical and systematic) to [FORMULA] (combined statistical and systematic) in the energy range discussed here. A detailed study of the systematic errors reveals that a non-changing composition cannot be excluded.

Key words: ISM: cosmic rays

* Now at Forschungszentrum Karlsruhe, P.O. Box 3640, 76021 Karlsruhe, Germany
** Now at Line Consulting AG, Hamburg
*** Now at Universidad Autónoma de Barcelona, Institut de Física d'Altes Energies, 08193 Bellaterra, Spain

Send offprint requests to: R. Plaga (plaga@mppmu.mpg.de)

© European Southern Observatory (ESO) 2000

Online publication: July 7, 2000

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