Branching Ratios of Reactions ofπ−Mesons Stopped in Hydrogen and Deuterium

Abstract

We measure the Panofsky ratio $P=\frac{\omega ({\pi }^{-}+p\to {\pi }^0+n)}{\omega ({\pi }^{-}+p\to \gamma +n)}$ and the branching ratio $S=\frac{\omega ({\pi }^{-}+d\to n+n)}{\omega ({\pi }^{-}+d\to \gamma +n+n)}$ by stopping ${\pi }^{-}$ mesons in liquid hydrogen and liquid deuterium and detecting the $\gamma$ rays produced. A high-resolution $\gamma$-ray spectrometer of the 180-deg-focusing type is employed. Sixty-six Geiger tubes and nine scintillation counters are used in the spectrometer to define the electron-positron orbits, providing an intrinsic instrument resolution of 0.8%. The values we obtain for the branching ratios are $P=1.51\mathrm{}\pm 0.04$ and $S=3.16\mathrm{}\pm 0.12$. This value for $P$ is in good agreement with that obtained in previous measurements, while the value for $S$ is significantly larger than previous results. With regard to the conventional phenomenological analysis of $S$-wave pion physics, the Panofsky ratio is in good agreement, whereas the value obtained in this experiment for the branching ratio $S$ is considerably larger than predicted.