Branching Ratios of Reactions ofπ−Mesons Stopped in Hydrogen and Deuterium

Measurement ofγrays from antiproton-deuterium annihilation at rest

“…Using t h e Panofsky ratio [29] a n d t h e branching ratio B (T-d --t y n n ) = 0 . 2 5 [26,27], we find t h a t t h e observed a m o u n t c a n b e interpreted by contamination of H, in liquid D2 by 0.9% (in moll. T h e above-mentioned structure may also include a small a m o u n t of photons coming from n-d -nOnn with no-yy.…”

“…2 X which is derived by multiplying the following three numbers: the n multiplicity of 1.78 per jid annihilation [from a of Eq. (5) and the n -multiplicity of 1.57 per p7a and of 2.07 per pn annihilation as seen in Table 1111, the branching ratio B (.rr-d -+ y nn ) =0.25 [26,27], and the average probability that a a-meson should stop in the liquid D,=0.94% corresponding to the pion range of 7 cm in deuterium. The last number was deduced from the Tmomentum distribution calculated by a Monte Carlo simulation [I] for pp annihilation.…”

“…In pd annihilation, the y rays arising from capture of secondary n~ by another deuterium should be localized dominantly around 129 MeV [26][27][28] corresponding to radiative capture of 7r~ (7r~d-^ynn) with a far smaller amount of charge exchange (7r~d-^7r°nn-^yynn) which will produce a nearly box-type spectrum between 62 and 74 MeV. Consequently, the y-ray spectrum from TT~ capture should be much simpler in deuterium than in hydrogen.…”

“…Actually, however, contamination of neutrons could make the apparent "y-ray" spectrum complicated. Neutrons arising from ir~d at rest into nn (B -15% [26,27]) and ynn (B-25% [26,27]) were mistaken as y rays on Nal because no separation between y rays and neutrons was made. The former could mimic y rays with energies less than 68 MeV and the latter as small as 9 MeV.…”