Next-to-Leading-Order Corrections and Factorization for Transverse Single-Spin Asymmetries

We present next-to-leading-order QCD corrections for the cross sections for ℓp^{↑}→hX and ℓp^{↑}→jetX with transversely polarized initial protons. These cross sections are known to be power-suppressed in QCD and probe twist-3 parton correlation functions in the proton. Our calculation exhibits the full complexity of a perturbative QCD analysis beyond leading power, involving in particular various derivatives of the parton correlation functions. We demonstrate that collinear factorization for these single-spin observables holds at one loop. We also present exploratory phenomenological results for the NLO single-spin asymmetry in ep^{↑}→hX and compare to data from the HERMES experiment.