Single-spin asymmetries and invariant cross sections of the high transverse-momentum inclusive pi 0 production in 200 GeV/c pp and p-barp interactions.

The pi(0) inclusive and semi-inclusive, single-spin asymmetries have been measured using transversely polarized, 200-GeV/c proton and antiproton beams colliding with an unpolarized hydrogen target. The measured asymmetries are consistent with zero within the experimental uncertainties for the kinematic region -0.15 3 GeV/c were not correct. These data indicate that PQCD expectations seem confirmed and the higher-twist contribution to the single-spin asymmetry in pi(0) production at x(F)=0 is not large. Additional evidence for such a conclusion comes from the measurement of a semi-inclusive pi(0) asymmetry, where associated charged particles are detected opposite to the pi(0) azimuthal direction. This experiment also provides high-statistics data on the inclusive pi(0) cross sections for pp and collisions at root s approximate to 19.4 GeV.