New measurement of the asymmetry parameter for the Sigma +-->p gamma decay.

Abstract

The asymmetry parameter ${\ensuremath{\alpha}}_{\ensuremath{\gamma}}$ for the ${\ensuremath{\Sigma}}^{+}$\ensuremath{\rightarrow}p\ensuremath{\gamma} decay has been measured with counter techniques. From a sample of about 190 ${\ensuremath{\Sigma}}^{+}$\ensuremath{\rightarrow}p\ensuremath{\gamma} decays, the asymmetry parameter is found to be ${\ensuremath{\alpha}}_{\ensuremath{\gamma}}$=-0.86\ifmmode\pm\else\textpm\fi{}0.13\ifmmode\pm\else\textpm\fi{}0.04, where the quoted errors are statistical and systematic, respectively. The present result confirms with better accuracy the large and negative value for ${\ensuremath{\alpha}}_{\ensuremath{\gamma}}$ measured by two previous bubble-chamber experiments. The branching ratio is also found to be (1.30\ifmmode\pm\else\textpm\fi{}0.15) \ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$, which is consistent with previous measurements.