The Gamma-Ray Spectrum Resulting from Capture of Negativeπ-Mesons in Hydrogen and Deuterium

π^- mesons produced in an internal wolfram target bombarded by 330-Mev protons in the 184-inch cyclotron are absorbed in a high pressure hydrogen target. The resulting gamma-ray spectrum is analyzed outside the shielding of the cyclotron by means of a 30-channel electron-positron pair spectrometer. The principal results are as follows. (1) The gamma-rays result from two competing reactions: π^-+p→n+γ and π^-+p→n+π⁰; π⁰→2γ. (2) The ratio between the π⁰ yield to the single gamma-ray yield is =0.94±{}0.20. (3) The mass difference between the π^- meson and the π⁰ meson is given by 10.6±{}2.0 electron masses. (4) The π^- mass is 275.2±{}2.5 electron masses. The large mass difference between π^- and π⁰ precludes the conclusion that the unexpectedly small π⁰ to γ ratio is due to the small amount of momentum space available for π⁰ emission. It rather indicates that π⁰ emission is slowed down by the nature of the coupling of the π⁰ field to the nucleons. The experiment has been repeated by substituting D₂ for H₂ in the vessel. The result is that the reaction π^-+D→2n and π^-+D→2n+γ compete in the ratio 2: 1. The reaction π^-+D→2n+π⁰ is absent.