The two-spin parameter ALL in inclusive π0 productionby longitudinally-polarized protons and antiprotons on a longitudinally-polarized proton target has been measured at the 200 GeV Fermilab spin physics facility, for π0's at xF=0 with 1≤pt≤3 GeV/c. The results exclude, at the 95% confidence level, values of ALL (pp) > 0.1 and < - 0.1 for π0'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.
ASJC Scopus subject areas
- Nuclear and High Energy Physics