Observations onp¯dAnnihilations at Rest into Two Pions

The ratio $\frac{(\overline{p}d\to {\pi }^{-}{\pi }^0{p}_s)}{(\overline{p}d\to {\pi }^{-}{\pi }^{+}n)}$ at rest, with spectator momenta $\lesssim 300 \frac{\mathrm{MeV}}{c}$, has been measured and found to be 0.68 ± 0.07. This implies that (75 ± 8)% of the annihilations in deuterium into two pions come from odd $\overline{N}N$ orbital angular momenta, in disagreement with the $S$-state-dominance hypothesis. It has also been observed that the $\overline{p}d\to {\pi }^{-}{\pi }^0{p}_s$ production rate depends on the spectator momentum, which suggests energy-sensitive $\overline{N}N$ phenomena near threshold.