Study of eta and eta' production in antineutron-proton annihilations

The annihilation fractions and cross sections for the antin-p annihilation reaction in flight (50–400 MeV/c) into eta pi+ and eta' pi+ final states have been measured. The first ones follow the trend expected for P wave annihilations. From the ratios of the yields an evaluation of the pseudoscalar mixing angle in the standard form is possible. The value found shows that for pseudoscalar meson production from P wave the Quark Line Rule is not grossly violated.