Mass Spectrum of Shower Particles from Cosmic-Ray Interactions

The masses of particles with an ionization less than about twice the minimum value emitted in cosmic-ray stars in a photographic emulsion have been determined by observations on the grain density and scattering of suitably long tracks. About 100 tracks with an average length of 16.5 mm were analyzed using a single emulsion exposed to cosmic rays in a high-altitude balloon flight of nine hours duration. The results show groups of pions, protons, deuterons, heavy mesons with mass $\sim 925m_e$ and the possibility of a group with mass closer to that of the proton. This latter is uncertain, however, with the present resolution and could be a statistical fluctuation on the edge of the proton distribution.