Next-to-leading order QCD corrections toATTfor prompt photon production

We present a next-to-leading order QCD calculation of the cross section for isolated large-$p_T$ prompt photon production in collisions of transversely polarized protons. We devise a simple method of dealing with the phase space integrals in dimensional regularization in the presence of the $\cos \left(2\mathrm{}\Phi \right)$ azimuthal-angular dependence occurring for transverse polarization. Our results allow us to calculate the double-spin asymmetry $A_{\mathrm{TT}}^{\gamma }$ for this process at next-to-leading order accuracy, which may be used at BNL RHIC to measure the transversity parton distributions of the proton.