OBSERVATION OF ETA' AND PHI-MESON PRODUCTION VERY CLOSE TO THRESHOLD IN THE PD-]HE-3 X REACTION

The production of eta' (958) and phi (1020) mesons has been studied ve ry close to threshold in the inclusive p d --> He-3 X reaction. The co mplicated phase space acceptance problem caused by rapidly changing ki nematics close to threshold has been carefully treated. The measured a veraged squared amplitudes \f\(2) at threshold are 0.9 and 2.4 nb/sr f or the eta' and phi meson. Our results are in remarkable agreement wit h predictions of a two-step model, which uses existing pi(-)p --> n X data as input. However the ratio of phi to omega production seems at v ariance with naive expectations based on the Okubo-Zweig-Iizuka rule.