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

${\pi }^{-}$ 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: ${\pi }^{-}+p\to n+\gamma$ and ${\pi }^{-}+p\to n+{\pi }^0$; ${\pi }^0\to 2\gamma$. (2) The ratio between the ${\pi }^0$ yield to the single gamma-ray yield is =0.94±0.20. (3) The mass difference between the ${\pi }^{-}$ meson and the ${\pi }^0$ meson is given by 10.6±2.0 electron masses. (4) The ${\pi }^{-}$ mass is 275.2±2.5 electron masses. The large mass difference between ${\pi }^{-}$ and ${\pi }^0$ precludes the conclusion that the unexpectedly small ${\pi }^0$ to $\gamma$ ratio is due to the small amount of momentum space available for ${\pi }^0$ emission. It rather indicates that ${\pi }^0$ emission is slowed down by the nature of the coupling of the ${\pi }^0$ field to the nucleons. The experiment has been repeated by substituting ${\mathrm{D}}_2$ for ${\mathrm{H}}_2$ in the vessel. The result is that the reaction ${\pi }^{-}+D\to 2n$ and ${\pi }^{-}+D\to 2n+\gamma$ compete in the ratio 2: 1. The reaction ${\pi }^{-}+D\to 2n+{\pi }^0$ is absent.