Energy spectrum and mass composition of primary cosmic radiation in the region above the knee from the GAMMA experiment

摘要

The energy spectrum of the primary cosmic radiation in the energy range 1 – 100 PeV and the extensive airshower (EAS) characteristics obtained on the basis of the expanded data bank of the GAMMA experiment (Mt. Aragats,Armenia) are presented. With increased statistics we confirm our previous results on the energy spectrum. Thespectral index above the knee is about -3.1, but at energies beyond 20 PeV a flattening of the spectrum is observed.The existence of the bump at about 70 PeV is confirmed with a significance of more than 4σ . In the energy rangeto the primary energy. This suggests an approximately constant depth of the EAS maximum in this energy range.This is evidence in favour of an increasing average mass of primary particles at energies above 20 PeV. The additionalsource scenario, which is a possible explanation of the bump in the spectrum, also leads to the conclusion of increasingmass of the primary cosmic rays. A comparison with the data of other experiments is presented.