New searches for the C-noninvariant decay pi 0-->3 gamma and the rare decay pi 0-->4 gamma.

Abstract

A search for the charge-conjugation-noninvariant decay ${\ensuremath{\pi}}^{0}$\ensuremath{\rightarrow}3\ensuremath{\gamma} has been made using the Crystal Box of the Los Alamos Meson Physics Facility. No signal in excess of background was observed, resulting in a branching-ratio upper limit of 3.1\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}8}$ (90% C.L.). A new upper limit of 2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}8}$ (90% C.L.) was also established for the allowed decay ${\ensuremath{\pi}}^{0}$\ensuremath{\rightarrow}4\ensuremath{\gamma}.