Occhialini’s Contribution to the Discovery of the Pion. An Interview by L. Gariboldi

The paper “Processes Involving Charged Mesons” [1, 2] signed by Cesare Mansueto Giulio Lattes, Hugh Muirhead, Giuseppe Paolo Stanislao Occhialini, and Cecil Frank Powell was published in the May 24th, 1947 issue of Nature. In the introduction to this paper we can read the following announcement: “we have found evidence of mesons which, at the end of their range, produce secondary mesons.” The primary mesons, whose discovery was announced with these very words, were at first thought to be the long searched for pions, the particles responsible for the strong interaction predicted by Hideki Yukawa in 1935, the secondary mesons being the muons discovered by Carl Anderson and Seth Henry Neddermeyer in 1937. and identified with a particle different from Yukawa’s meson by Marcello Conversi, Ettore Pancini and Oreste Piccioni in Rome.