Ultra-high energy cosmic rays: 40 years retrospective of continuous observations at the Yakutsk array: Part 2. Mass composition of cosmic rays at ultra high energies

Abstract

Abstract. In the paper, we describe methods for the analysis and present results for the mass composition of cosmic rays, obtained by using these techniques over a large time span. The data were obtained at the Small Cherenkov array over a 20 -year period of continuous observation and 40 -years of observations at the main Yakutsk array. Our experimental data indicate a change in the mass composition in the energy range 10 16 -10 18 eV and is confirmed by independent results obtained by other EAS arrays.

Some results from the Yakutsk array experiment and the status of the modernization program

“…The main methods for estimation of the mass composition of CRs are based on measurements of the mean value of and fluctuations in x max , and the muon content of showers. The results from the Yakutsk array obtained using these two methods [21,22] are shown in the central panel of Fig. 6, in comparison with available data from other experiments.…”

Mass composition of cosmic rays determined by muon fraction with $\varepsilon_{thr.} \geq$ 1 GeV in air showers with energy greater than 5 EeV

“…At the largest experiments for the study of air showers, recently, interesting data have been obtained on cosmic rays in the energy region above 1 EeV: the cosmic ray spectrum [17,18], the mass composition [19][20][21][22][23][24][25][26], and the anisotropy of the arrival of particles with highest energies [27][28][29] . Verification of the obtained data is still small and further research in these areas is required.…”