e+e- pair photoproduction in crystals with account for lepton, antilepton and γ-quantum longitudinal spin orientations

The photoproduction of lepton-antilepton pair in crystals is being investigated theoretically with an allowance for spin correlations of all the initial and final particles. The expression for the amorphous and interference parts of the photoproduction cross sections of an electron-positron pair in a single crystal is obtained. The relative probability of production of a pair with spiralities Ssub(+)Ssub(-)=+1 and Ssub(+)Ssub(-)=-1 and the degree of longitudinal polarization of an e+e pair as a whole are determined. The figure presents the energy dependence of the photoproduction cross section of an e+e- pair in a single crystal of a diamond, with an account of the spin correlations of e+γ, and the energy distribution of the degree of longitudinal polarization of a positron for a diamond crystal and an amorphous substance. The curves are of a diffraction nature, and the crystal structure of a target strongly affects the values under investigation