First results for the two-spin parameter ALL in 0 production by 200 GeV polarized protons and antiprotons
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The two-spin parameter ALL in inclusive 0 productionby longitudinally-polarized protons and antiprotons on a longitudinally-polarized proton target has been measured at the 200 GeV Fermilab spin physics facility, for 0's at xF=0 with 1pt3 GeV/c. The results exclude, at the 95% confidence level, values of ALL (pp) > 0.1 and < - 0.1 for 0's produced by protons, and values of ALL (pp) > 0.1 and < -0.2 for incident antiprotons. The relevance of ALL (pp) for the gluon spin density is discussed. The data are in good agreement with "conventional", small or zero, gluon polarization. 1991.