Spin-parameter measurements in. lambda. and K/sub S/ production

The Brookhaven Alternating Gradient Synchrotron polarized proton beam incident on a beryllium target was used for inclusive ..lambda.. production at beam momenta of 13.3 and 18.5 GeV/c. The beam polarization was transverse to the beam direction with magnitude 0.63 at 13.3 GeV/c and 0.40 at 18.5 GeV/c. The ..lambda.. polarization was measured and found to be in agreement with results from earlier experiments which used unpolarized proton beams. Analyzing power A/sub N/ and spin transfer D/sub N//sub N/ of the ..lambda..'s were both measured and compared with a hyperon-polarization model in which the polarization arises from a Thomas-precession effect. There is good agreement with its predictions: A/sub N/ = 0 and D/sub N//sub N/ = 0. In particular, our measurement of = -0.009 +- 0.015 supports the idea that the valence quarks carry all of the hadron spin, since this assumption is implicit in the model's use of SU(6) wave functions to form final-state hadrons from beam fragments and sea quarks. The presence of substantial K/sub S/ samples at both beam momenta and Lambda-bar's at 18.5 GeV/c prompted a measurement of their analyzing powers, which yielded A/sub N/(K/sub S/) = -0.094 +- 0.012 at 13.3 GeV/c beam momentum and -0.076more » +- 0.015 at 18.5 GeV/c, and A/sub N/(Lambda-bar) = 0.03 +- 0.10.« less