Cloud-Chamber Evidence for a Charged Counterpart of theθ0Particle

A photograph obtained in a Wilson cloud chamber, operated in a magnetic field, shows the following unusual event: A positive particle, produced in an interaction above the cloud chamber, decays in flight into a positive particle less massive than a $K$ meson. Four other lightly ionizing particles also originate from the decay point; these appear in the form of two small-angle pairs, each pair consisting of one positive and one negative particle. The observed momenta and ionizations are consistent with three of these four particles being either electrons or mesons; the fourth must be an electron.