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 π⁰→γ+e⁺+e^- was found to be 0.0053±{}0.0009; for the reaction π^-+p→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.