Spin-parameter measurements in inclusiveΣ0production

We have measured the polarization P, the analyzing power A, and the polarization transfer D of ${\Sigma }^0$’s produced inclusively by a polarized proton beam at 18.5 GeV/c. Our data cover a region of moderate $p_T$ (average 1 GeV/c) and Feynman x up to 0.75. We find agreement with a previous measurement of the ${\Sigma }^0$ polarization P. We observe nonzero values for A and D, but they are significantly smaller than predictions based on a simple parton-recombination model. We have extended this model to include finite transversity spin flips, which improves agreement with the data considerably.