DYNAMICAL SEMIGROUP DESCRIPTION OF COHERENT AND INCOHERENT PARTICLE-MATTER INTERACTION

The meaning of statistical experiments with single microsystems in qua ntum mechanics is discussed and a general model in the framework of no nrelativistic quantum field theory is proposed to describe both cohere nt and incoherent interaction of a single microsystem with matter. Com pactly developing the calculations with superoperators, it is shown th at the introduction of a time scale linked to irreversibility of the r educed dynamics directly leads to a dynamical semigroup expressed in t erms of quantities typical of scattering theory. Its generator consist s of two terms, the first linked to a coherent wavelike behavior, the second related to an interaction having a measuring character, possibl y connected to events the microsystem produces propagating inside matt er. In case these events breed a measurement, an explicit realization of some concepts of modern quantum mechanics (''effects'' and ''operat ions'') arises. The relevance of this description to a recent debate q uestioning the validity of ordinary quantum mechanics to account for s uch experimental situations as, e.g., neutron interferometry is briefl y discussed.