LXI. On the mass of the Λ0-particle

Summary In a stack of stripped photographic emulsions, twenty events of type 2+0 n have been observed, in each of which the outgoing particles are a proton and a negative π-meson respectively; the latter particle was identified by the characteristic star it produced when brought to rest in the emulsion. Assuming that each of these events represents the decay in flight of a neutral hyperon according to the scheme Λ 0→π -+P+Q, values of the energy release Q have been calculated. In eleven of the events the proton could be traced to the end of its range; the energies of both particles could then be deduced using appropriate range-energy relations. In the remaining nine examples, the energy of the proton was deduced from grain density considerations and was accordingly less well determined.