An uninvited guest: The positron in early 1930s physics

A few months before its “official” discovery in September 1932 by Anderson at Cal Tech in Pasadena, the positron was almost simultaneously observed by no less than two additional research teams: one at Cavendish Laboratory in Cambridge, England, and one at Institut du Radium in Paris, France. In this paper, we examine this curious case of multiple independent observations by studying the primary literature. This study identifies the motivations that led these researchers to independently design the experiments suitable for the detection of this novel particle and shows that none of these teams were looking for a positive electron.