STRANGENESS-PRODUCING REACTIONS POLARIZATION OBSERVABLES IN $p + -K+K REACTIONS AT 2.9 GeV S. Bossolasco, M.P. Bussa, L. Fava, L. Ferrero, R. Garfagnini, A. Grasso, A. Maggiora, D. Panzieri, G. Piragino, F. Tosello, and G. Zosi Istituto di Fisica and INFN, Torino, Italy L.C. Bland, W.W. Jacobs, Y. Kim, and S.E. Vigdor Indiana University and Indiana University Cyclotron Facility, Bloomington, Indiana 4 74 08 J. Arvieux, Y. Bedfer, R. Bertini, and F. Brochard Laboratoire National Saturne, Saclay, France F. Balestra INFN and Universita di Cagliari, Cagliari, Italy I.V. Falomkin, V.I. Lyascenko, G.M. Maneva, G.B. Pontecorvo, A.M. Rozhdestvensky, M.G. Sapozhnikov, P.P. Temnikov, V.I. Travkin, and V.I. Tretyak JINR, Dubna, Russia We have initiated a collaboration to study polarization effects in exclusive hyperon- production reactions at the Saturne synchrotron in Saclay. The primary motivation for this work is the apparently simple systematic behavior1 of hyperon polarizations measured in earlier inclusive production experiments at higher bombarding energies (&=5-60 GeV). The majority of the measurements have been made for Ao production, but data exist as well for heavier hyperons that also decay via the weak interaction, where the parity- violating decay asymmetry allows a direct inference of the parent's polarization. Sizable polarizations ( > 20%) have been observed, of opposite sign for A0 and C' production, with a characteristic dependence on the transverse and longitudinal momenta of the produced hyperon,' but essentially independent of the bombarding energy1 and (judging from a single experiment on A0 production with a polarized incident beam2 ) of the polarization state of the proton beam. These systematics suggest that there is some simple mechanism for polarizing strange quarks when they are "boosted" from the "sea" in the initial nucleons to the status of a "valence" quark in the outgoing hyperon.' Various models for such a mechanism have been proposed.3-5 They do not, however, appear to have real predictive power: the quantitative analysis of new data within these models has most often been handled by adding new adjust able parameters to the calculations. 122