The neutrino, neutron, positron, and muon were discovered in the 1930s. The pion and strange particles had their turn in the late forties. During the fifties, which saw the change from dependence on natural sources to accelerators in the study of particles, the particles and their properties were sorted out, the strange particles were systematized, the first particle resonances were seen, and parity was found to be violated, with a concomitant clarification of the weak interaction. It was an exciting time. The field advanced rapidly. I was young and played my part in this adventure.

Cosmic rays and muon decay

For me, particle physics began in 1947, when I was a graduate student at the University of Chicago. Enrico Fermi gave a seminar on the results of the Conversi, Pancini, and Piccioni experiment in which he explained that because the negative mesotrons rapidly find their way to the atomic K shell, the observed long lifetimes were incompatible with the role of these mesons as Yukawa particles. It was a beautiful and important experiment, and Fermi's explanation was extraordinarily lucid, as well as stimulating and exciting. The puzzle was at least in part cleared up a few months later when the Bristol group discovered the pion in nuclear emulsions.

It was a great privilege to be a student in that department at that time. There were excellent teachers: Fermi, Edward Teller, Willie Zachariasen, and Maria Mayer, to name a few. Fermi's courses, in particular, were models of transparent and simple organization of the most important concepts.