Hard exclusive meson production at next-to-leading order

We evaluate perturbative next-to-leading order corrections to the hard exclusive leptoproduction of π+ mesons on a transversely polarized proton target. A model dependent study shows that these corrections can be large. We analyze the scale dependence and explore the Brodsky–Lepage–Mackenzie scale setting procedure. Although the predictions for the cross section suffer from theoretical uncertainties, the transverse nucleon single spin asymmetry turns out to be a rather stable observable since higher order effects approximately cancel there.