STRANGE PARTICLES: DECAYSl

This review deals with the theory of weak interactions of elementary particles, with particular attention to leptonic decays of strange particles (K mesons and hyperons). We shall altogether disregard slow processes taking place in nuclei (nuclear {3-decay, muon capture in nuclei, hyperfrag­ ment decay). Without attempting to embrace all the trends now existing in the theory of strange particle decays, we shall give below one of the possible approaches, This approach is based on the hypotheses of the compound model of strongly interacting particles and of the universal weak interaction. Of essential importance in the decays of mesons and baryons are virtual strong interactions. As no consistent theory of strong interactions exists at present, we shall take them into account phenomenologically. We shall not consider small corrections caused by virtual photons. In Section 2 the properties of weak interactions are discussed. Muon decay is considered in Section 3. In this process the nature of the weak interaction is not obscured by virtual strong interactions. The fourth section deals with interactions between leptons and strongly interacting particles involving no change of strangeness of the latter. These interactions are responsible for such processes as neutron decay, muon capture by the proton, charged pions decays, and several hyperon decays which have not been observed so far. Section 5 considers interactions of leptons with strongly interacting particles, involving a change of strangeness of the latter. They are responsible for the leptonic decays of K mesons and hyperons. Section 6 is devoted to non­ leptonic decays of strange particles. Lack of space has made it impossible to embrace all original theoretical works on the questions considered and even more so to cover all experimental papers. The reader will find more exhaustive information on the questions dealt with in this review in the proceedings of conferences on the physics of elementary particles ( 1 to 5) and in a number of reviews (6 to 19) .