Charge-Exchange Of Stopped Pi-In Deuterium - Experiment And Theory

The branching ratio for the reaction ${\\ensuremath{\\pi}}^{\\ensuremath{-}}d\\ensuremath{\\rightarrow}{\\ensuremath{\\pi}}^{0}\\mathrm{nn}$ has been measured for the first time by stopping the ${\\ensuremath{\\pi}}^{\\ensuremath{-}}$ in a liquid-deuterium target and detecting the two decay $\\ensuremath{\\gamma}'\\mathrm{s}$ in two large NaI detectors. A branching ratio $(\\mathrm{B}.\\mathrm{R}.)=\\frac{\\ensuremath{\\omega}({\\ensuremath{\\pi}}^{\\ensuremath{-}}d\\ensuremath{\\rightarrow}{\\ensuremath{\\pi}}^{0}nn)}{\\ensuremath{\\omega}({\\ensuremath{\\pi}}^{\\ensuremath{-}}d\\ensuremath{\\rightarrow}\\mathrm{all})}$ of (1.45 \\ifmmode\\pm\\else\\textpm\\fi{} 0.19) \\ifmmode\\times\\else\\texttimes\\fi{} ${10}^{\\ensuremath{-}4}$ has been measured; the predicted B.R. lies in the range 1.39 \\ifmmode\\times\\else\\texttimes\\fi{} ${10}^{\\ensuremath{-}4}$ to 1.59 \\ifmmode\\times\\else\\texttimes\\fi{} ${10}^{\\ensuremath{-}4}$.