The depth of maximum shower development and its fluctuations: cosmic ray mass composition at E0≥1017 eV
04 Jul 2011
Yu. G. Shafer Institute for Cosmophysical Research and Aeronomy, 31 Lenin Ave., 677980 Yakutsk, Russia
Abstract. We present new data on Cherenkov light observations obtained during 1994–2009 period, after a modernization of the Yakutsk EAS array. A complex analysis of xmax and its fluctuations σ(xmax) was performed in a wide energy range. With the new data, according to QGSJet II model, an estimation was made of cosmic rays mass composition for E0~1017–3×1019 eV. The result points towards a mixed composition with a large portion of heavy nuclei at E0~1017 eV and the dominance of light nuclei at E0~1019 eV. The analysis of σxmax energy dependence for the same energies qualitatively confirms this result. A shape of xmax distribution at fixed energy 1018 eV is analysed to make more precise conclusion on cosmic ray mass composition.