The discoveries of the strange particles, 1943–1959.
The elucidation of the π → µν decay sequence left particle physics in a relatively simple state. Yukawa’s particle had been found and the only unanticipated particle was the muon, of which I. I. Rabi is said to have remarked “Who ordered that?” The question remains unanswered. The cosmic-ray experiments of the next few years quickly and thoroughly destroyed the simplicity that had previously prevailed. The proliferation of new particles, many with several patterns of decay, produced great confusion. The primary source of confusion was whether each new decay mode represented a new particle or was simply an alternative decay for a previously observed particle. Continued experimentation ...