Spin-parameter measurements in Λ and KS production

The Brookhaven Alternating Gradient Synchrotron polarized proton beam incident on a beryllium target was used for inclusive Λ 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 Λ polarization was measured and found to be in agreement with results from earlier experiments which used unpolarized proton beams. Analyzing power A_N and spin transfer D_NN of the Λ'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_N=0 and D_NN=0. In particular, our measurement of <D_NN>=-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_S samples at both beam momenta and Λ¯'s at 18.5 GeV/c prompted a measurement of their analyzing powers, which yielded A_N(K_S)=-0.094+/-0.012 at 13.3 GeV/c beam momentum and -0.076+/-0.015 at 18.5 GeV/c, and A_N(Λ¯)=0.03+/-0.10.