Estimation of the composition of ultra-high energy cosmic rays using the muon correlation method based on Yakutsk EAS array data

In this article a new method is proposed for estimating the mass composition of cosmic rays in individual events with energies above $1.25\times {10}^{19}$ eV. It is based on a joint analysis of experimental data and simulation results obtained using the QGSJet-II.04 model for muons with threshold energy $E_{\mu }=1.0\times \cos \theta$ GeV in air showers with zenith angles up to 60 degrees. The data from ground-based and underground scintillation detectors of the Yakutsk EAS array were used. Separate groups of nuclei and other primary particles were found.