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

Abstract

${\ensuremath{\pi}}^{\ensuremath{-}}$ 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: ${\ensuremath{\pi}}^{\ensuremath{-}}+p\ensuremath{\rightarrow}n+\ensuremath{\gamma}$ and ${\ensuremath{\pi}}^{\ensuremath{-}}+p\ensuremath{\rightarrow}n+{\ensuremath{\pi}}^{0}$; ${\ensuremath{\pi}}^{0}\ensuremath{\rightarrow}2\ensuremath{\gamma}$. (2) The ratio between the ${\ensuremath{\pi}}^{0}$ yield to the single gamma-ray yield is =0.94\ifmmode\pm\else\textpm\fi{}0.20. (3) The mass difference between the ${\ensuremath{\pi}}^{\ensuremath{-}}$ meson and the ${\ensuremath{\pi}}^{0}$ meson is given by 10.6\ifmmode\pm\else\textpm\fi{}2.0 electron masses. (4) The ${\ensuremath{\pi}}^{\ensuremath{-}}$ mass is 275.2\ifmmode\pm\else\textpm\fi{}2.5 electron masses. The large mass difference between ${\ensuremath{\pi}}^{\ensuremath{-}}$ and ${\ensuremath{\pi}}^{0}$ precludes the conclusion that the unexpectedly small ${\ensuremath{\pi}}^{0}$ to $\ensuremath{\gamma}$ ratio is due to the small amount of momentum space available for ${\ensuremath{\pi}}^{0}$ emission. It rather indicates that ${\ensuremath{\pi}}^{0}$ emission is slowed down by the nature of the coupling of the ${\ensuremath{\pi}}^{0}$ 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 ${\ensuremath{\pi}}^{\ensuremath{-}}+D\ensuremath{\rightarrow}2n$ and ${\ensuremath{\pi}}^{\ensuremath{-}}+D\ensuremath{\rightarrow}2n+\ensuremath{\gamma}$ compete in the ratio 2: 1. The reaction ${\ensuremath{\pi}}^{\ensuremath{-}}+D\ensuremath{\rightarrow}2n+{\ensuremath{\pi}}^{0}$ is absent.