On processes in the interaction of γ-quanta with unstable particles

Abstract

This paper deals with various inelastic processes occuring in the collisions of fast particles with the nuclei neither excited nor transformed. At q 2 = 0 ( q 2 being the invariant square of the momentum transfer to the nucleus) the amplitude of these processes has a pole involving virtual photons. Therefore at sufficiently small q 2 the virtual photon exchange makes a larger contribution to the amplitude than the exchange of strongly interacting particles. This makes it possible to connect at small q 2 the cross section of the process under study and that of the process at work between the γ-quantum and the incident particle. Given q 2 and E L ⪢ m ( E L being the energy of incident particle in the laboratory coordinate system and m its mass), the energy w of the particles produced in the reaction in their centre-of-mass system is restricted by the condition w 2 − m 2 < 2 E L √ q 2. The relation between the above-mentioned cross sections, equivalent to one following from the Weizsäcker-Williams method, is obtained in the present paper by a covariant method, and the conditions of applicability of this relation are discussed, in particular for strongly interacting particle processes. An appraisal is made of the contribution made by the processes involving the Coulomb nuclear field to the total cross section of interaction between the incident particle and the nucleus. The processes at work in the Coulomb field of the nucleus, such as the bremsstrahlung of π or K-mesons, the conversion of π-mesons into two π-mesons and the transformations of a Λ 0-particle into Σ 0-particle are analyzed in detail.