The transverse nucleon single-spin asymmetry for the semi-inclusive production of photons in lepton-nucleon scattering

We study the semi-inclusive production of real, high-p(T), isolated photons in unpolarized and polarized lepton-proton collisions, lp -> l gamma X. In particular we analyze the transverse nucleon single-spin asymmetry within the collinear twist-3 formalism in perturbative QCD to leading order (LO) accuracy. We find that this spin asymmetry is generated by twist-3 dynamical quark-gluon-quark (qgq) correlations in the nucleon through the so-called soft-fermion and hard pole contributions. Hence, this process unprecedentedly allows for a point-by-point scan of the support of the dynamical qgqtwist-3 matrix elements F-FT(x, x') and G(FT)(x, x') in lepton-nucleon scattering experiments. (c) 2020 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).