Magnetic Deflection of Cosmic-Ray Mesons Using Nuclear Plates

An experiment has been carried out in which two nuclear plates, secured with an air gap separating their parallel emulsion surfaces in a perpendicular magnetic field, were used to obtain magnetic deflection measurements on cosmic-ray mesons near the top of the atmosphere. Details of the experimental procedure are given and sources of error are discussed. The signs of the charges of particles were determined, and confirmation obtained for the negative charge of $\sigma$-(star-producing) mesons, positive charge for $\pi$ and $\mu$ (observed disintegration), while both signs were observed for $\rho$-mesons (stopping without visible interaction). The relative abundances of the different meson types were investigated. For particles which stopped in the emulsion, range and magnetic curvature measurements allowed mass determinations which in the most favorable case of long path length gave, for an individual meson, a probable error of 15 percent in the mass determination. The values obtained were, for $\pi$- and $\sigma$-mesons, 270±20; for $\mu$ and $\rho$, 226±15. No evidence for light or very heavy mesons has been found so far.