Photoproduction of relativistic positronium atoms on extended targets

Abstract

It is shown that the yield of relativistic positronium atoms in photoproduction on extended targets is much larger than usually accepted.The cause of such difference is transparent. At high energies, when the positronium atom formation time $\tau_f$ becomes greater than the target length L, it is the free $e^+e^-$ pair that propagates through the target and the formation of positronium atoms take place out of the target.In the framework of the light-cone technique we consider the interaction of $e^+e^-$ pair with the screened Coulomb field of atoms in matter and obtain the analytical expressions for relativistic positronium atoms photoproduction cross sections on extended targets.The relations to free pair photoproduction on extended targets are discussed.