Mass composition of 10 17 - to 10 18 -eV primary cosmic rays according to data on the lateral distribution of radio emis
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EMENTARY PARTICLES AND FIELDS Experiment
Mass Composition of 1017 - to 1018 -eV Primary Cosmic Rays According to Data on the Lateral Distribution of Radio Emission from Extensive Air Showers N. N. Kalmykov*, A. A. Konstantinov, and O. V. Vedeneev Skobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow, 119991, Russia Received December 23, 2011; in final form, April 13, 2012
Abstract—Experimental data obtained for the lateral distribution of radio emission from extensive air showers (EAS) at the array of Moscow State University (30–34 MHz) and the LOPES array (40– 80 MHz) were compared with the results of calculations performed within a microscopic approach based on a Monte Carlo simulation of EAS (CORSIKA code). The same experimental data were used to reconstruct the distribution of the depth of the EAS maximum at cosmic-ray energies in the range of 1017 −1018 eV. The energy dependence of the depth of the EAS maximum was constructed for the case of data from the LOPES array, and the mass composition of cosmic rays was estimated for this case. From the resulting dependences, it follows that the mass composition shows a trend toward becoming lighter in the energy range being considered. DOI: 10.1134/S1063778812120083
1. INTRODUCTION Investigation of the mass composition of cosmic rays is of importance for addressing problems of cosmic-ray origin and propagation. Because of a low flux of cosmic rays whose energy is above 1015 eV, direct observations, including a direct measurement of the primary-particle charge, are impossible, and one has to rely on detecting extensive air showers (EAS), which are particle cascades generated by cosmic rays in the Earth’s atmosphere. Unfortunately, information about the primary-particle mass is inevitably blurred because of an indirect character of measurements and because of fluctuations in the EAS development. Therefore, one can in fact estimate only the group of nuclei that contains a particle that generated the shower being considered. The set of EAS parameters that are sensitive to the mass number A0 of cosmic rays includes the ratio of the number of muons to the number of electrons at the observation level and the depth of the maximum of EAS development. The first parameter is traditionally employed to estimate A0 within procedures where EAS are recorded via directly measuring the flux of shower particles [1–3]. The second parameter is considered within procedures based on detecting optical radiation from EAS (Cherenkov light [4, 5] and fluorescence [3, 6]). *
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The detection of EAS radio emission is the youngest method for recording cosmic rays among other procedures based on measuring electromagnetic radiation generated by EAS charged particles [7, 8]. In just the same way as in the case of Cherenkov light and fluorescence, the fundamental fact underlying the possibility of reconstructing the depth of the EAS maximum on basis of radio emission from a shower is that the detected radio signals are determined by its development in the atmos
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