Estimation of The Cosmic Ray Mass Composition at Energy Above 10 17 eV According to Scintillation Detectors of the Yakut
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ELEMENTARY PARTICLES AND FIELDS Experiment
Estimation of The Cosmic Ray Mass Composition at Energy Above 1017 eV According to Scintillation Detectors of the Yakutsk Array A. V. Glushkov1)* and A. Saburov1)** Received July 12, 2019; revised July 12, 2019; accepted July 12, 2019
Abstract—The lateral distribution of cascade particles was studied in extensive air showers initiated by cosmic rays with energies above 1017 eV. The study is based on experimental data of ground-based and ground-shielded (with ∼1-GeV energy threshold) scintillation detectors of the Yakutsk EAS array collected during the continuous observational period from 1977 to 2017. Particle density measured in experiment is compared to the results of simulations performed with the use of several ultra-high energy hadron interaction models. The best agreement between theory and experiment was obtained for QGSJET 01 and QGSJET II-04 models. Interpretation of our data has indicated that within the energy range (1−30) × 1017 eV the cosmic ray mass composition changes from nuclei of intermediate group towards protons. DOI: 10.1134/S1063778819660190
1. INTRODUCTION The data on energy spectrum and mass composition of ultra-high energy cosmic rays (CR) are crucial for solving the puzzle of their origin, acceleration, and propagation in the Universe. The only method of observation of such energetic CRs are extensive air showers (EAS) which have been actively studied worldwide for more than 40 years [1]. The exact mass composition of CR is still not known precisely, and without this knowledge it is difficult to understand the ins and outs of nuclear interactions in this energy region. At the Yakutsk EAS array (YEASA) the mass composition is estimated by the parameters of lateral distribution functions of different EAS components [2–6]. The key to the problem of CR mass composition is the depth of the maximum of shower curve xmax , which is connected to the mean atomic number A of primary particles via simple relation, which follows from superposition of nucleons [7]: exp.
log A =
xpmax − xmax , xpmax − xFe max
(1)
where the values of xmax were obtained from the experimental data (“exp.”) and from model calculations for primary protons (p) and iron nuclei (Fe). Here 1)
Yu.G. Shafer Institute of Cosmophysical Research and Aeronomy, Siberian Branch, Russian Academy of Sciences, Yakutsk, Russia. * E-mail: [email protected] ** E-mail: [email protected]
one cannot do without theoretical notion on EAS development. In the work [8] the responses of surface and muon detectors of YEASA have been calculated from particles in EAS with energy (E0 ) above 1017 eV. The lateral distribution functions (LDFs) of cascade particles were calculated from predictions obtained within the framework of ultra-high energy hadron interaction models QGSJET 01 [9], QGSJET II-04 [10], EPOS - LHC [11] and SIBYLL -2.1 [12] with the use of CORSIKA code [13]. The details of events selection, obtaining the mean LDFs for charged, electromagnetic (e-m) and muon components of EAS are discussed
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