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.