FIRST OBSERVATIONS OF PONTECORVO REACTIONS WITH A RECOILING NEUTRON

We report the first observations of Pontecorvo reactions of the type ( $) over bar pd --> Xn. We fully reconstruct the outgoing meson and, fo r antiprotons stopped in liquid deuterium, we measure: BR (pd --> pi(0 )n) = (7.03 +/- 0.72) x 10(-6), BR (($) over bar pd --> eta n) = (3.19 +/- 0.48) x 10(-6), BR (($) over bar pd --> omega n) = (22.8 +/- 4.1) x 10(-6), BR (($) over bar pd --> eta'n) less than or equal to 14 x 1 0(-6) (at 95% confidence level). Assuming charge independence, our res ult for ($) over bar pd --> pi(0)n is compatible with measurements of the only other observed Pontecorvo reaction ($) over bar pd --> pi(-)p . The experimental ratios between the above branching ratios are in fa ir agreement with both the statistical model and dynamical two-step mo dels (assuming N ($) over bar N annihilation into two mesons, with sub sequent absorption of one meson on the remaining nucleon). This agreem ent suggests that there may be appreciable rates for Pontecorvo reacti ons producing final state mesons with masses above 1 GeV.