High-xT single-spin asymmetry in pi0 and eta production at xF= 0 by 200 GeV polarized antiprotons and protons

A measurement of the single-spin asymmetry A(N) in P up + P --> pi-0 + X at 200 GeV with x(F) = O shows a transition in the production process from a "low-x(T)" regime with A(N) = 0, through an intermediate region of negative asymmetry, to a "high-x(T)" regime with A(N) > 0.3. This transition occurs at x(T) almost-equal-to 0.4 and is consistent with x(T)-scaling of A(N) in pion production using polarized beams or targets from square-root -s = 5.2 to 19.4 GeV. Results for A(N) in eta-production by polarized protons and in pi-0 production by polarized antiprotons are also presented.