Cross-sections and transverse single spin asymmetries in forward neutral pion production from proton collisions at s**(1/2) = 200- GeV
Phys.Rev.Lett. 92 (2004) 171801, 2004.
The collaboration

Abstract (data abstract)
Measurements of the production of forward high-energy $\pi^{0}$ mesons from transversely polarized proton collisions at $\sqrt{s}=200$ GeV are reported. The cross section is generally consistent with next-to-leading order perturbative QCD calculations. The analyzing power is small at $x_{F}$ below about 0.3, and becomes positive and large at higher $x_{F}$, similar to the trend in data at $\sqrt{s} \leq 20$ GeV. The analyzing power is in qualitative agreement with perturbative QCD model expectations. This is the first significant spin result seen for particles produced with $p_{T} > 1$ GeV/c at a polarized proton collider.