Diffusion Cloud-Chamber Study of Very Slow Mesons. I. Internal Pair Formation

A beam of negative pi and mu mesons was moderated to very low energies and allowed to enter a hydrogen-filled 20-atmosphere continuously sensitive cloud chamber. The various phenomena were observed and classified. A detailed study was made of the internal pair formation of mesonic gamma rays produced in the pion-hydrogen reactions. The conversion coefficient for the reaction ${\pi }^0\to \gamma +e^{+}+e^{-}$ was found to be 0.0053±0.0009; for the reaction ${\pi }^{-}+p\to n+e^{+}+e^{-}$ the coefficient is 0.0062±0.0013. Distributions in angle and energy were obtained from thirty-five of the forty-seven observed cases.