The density matrix ρ describing a decaying system can be expressed in terms of correlations among observables belonging to the subsystems. Due to this structure and to the difficulties in measuring higher rank tensors of decay products for a single decay event, it is found that the mean value of ρ cannot be determined, in general, from measurements on the decay products. We also discuss the consequences of this conclusion as far as tests of quantum mechanics are concerned.

We illustrate a generalization of Bell's inequality which is not limited to spin-1/2 or photon systems and does not depend on model-dependent assumptions. We then construct a specific class of examples, in terms of the decaying state and the correlated observables to be measured on the decay products, for which this inequality is violated by quantum mechanics. Finally we discuss the basic and practical problems involved in the measurement of these correlations.

We show that a local theory conforming to the requirement of reducing to usual quantum mechanics for single-particle states and describing two-particle correlations in terms of mixtures violates the condition of perfect anticorrelation between spin components in the case of Bohm's version of EPR.

The late Fifties were going to be eventful for physics in Italy. CERN had officially started its activities in the fall of 1954; however, the single European countries, Italy in the first place, were not in the condition to compete at the highest international level. A peculiar form of international distribution of the forms of research activities was then going to characterize those years, in particular as far as relationships between Italy and the United States were concerned. Italian physicists who (...) had become known in the United States and were in close relationship with their colleagues active on the opposite shore of the Atlantic obtained that the analysis of data collected in American labs.---in particular bubble chamber data---could be partially carried out in Italy. I try here to give a feeling of the kind of theoretical activity that involved Franco Selleri, among others, in that context. (shrink)