FROM PIONS TO PROTON DECAY: Tales of the Unexpected

Abstract

▪ Abstract  This account recalls early observations of elementary particles from cosmic ray experiments, using the nuclear emulsion technique. Discoveries in this field in the 1940s and 50s led to the development of high energy particle accelerators and associated detectors, resulting eventually in the observation of the quark and lepton constituents of matter and of the fundamental interactions between them, as described in the Standard Model. The concept of unification of the fundamental interactions led to the prediction of proton decay, and although this has not been observed, the unwanted background due to atmospheric neutrino interactions led to the discovery of neutrino oscillations and neutrino mass, and the first indications of new physics beyond that of the Standard Model. In all this research, unexpected developments have often played an important role.