Pontecorvo reactions in antiproton annihilation on deuterium

Pontecorvo reactions are antiproton annihilations on nuclei in which the final states are of a type not attainable from annihilations on free nucleons, for example pd→Xn, where X is a single meson. We report on the first observations of Pontecorvo reactions with a recoiling neutron, from p annihilation at rest in liquid deuterium. The results are B.R.(pd→π0n)=(6.63±0.59)×10−6, B.R.(pd→ηn)=(2.99±0.42)×10−6, B.R.(pd→ωn)=(21.2×3.5)×10−6, and B.R.(pd→η′n) ≤12×10−6 (at 90% C.L.). The result for pd→π0n is compatible with the only previously observed Pontecorvo reaction pd→π−p, assuming charge independence. The ratios of these branching ratios are compared to predictions based on dynamical models of the annihilation process which reproduce the general features of the data.