Search for a criterion for the mass estimation of the primary cosmic ray nuclei by the extensive air shower direct Cherenkov light for the SPHERE-3 telescope

SPHERE-3 detector, which is under design now, will incorporate not only a reflected Cherenkov light telescope but an imaging direct light telescope. In the present paper the length of the direct Cherenkov image is used as a parametr sensitive to the primary particle mass. A number of criteria for event separation by the primary masses is considered differing by the detector location with respect to the shower axis and their dependence on the types and values of the thresholds on the photon density and the pitch of the grid used for the description of the Cherenkov light angular distribution.