Transverse single-spin asymmetries in $\ell p^{\uparrow }\to hX$ within a TMD approach: Role of quasireal photon exchange

Abstract

We present an updated study of transverse single-spin asymmetries for the inclusive large-$P_T$ processes $\ell p^{\uparrow }\to hX$ and $\ell p^{\uparrow }\to \mathrm{jet}X$, within a transverse momentum-dependent approach, including the contribution of quasireal (Weizsäcker-Williams) photons. In the spirit of a unified transverse momentum-dependent scheme, predictions are obtained adopting the Sivers and transversity distributions and the Collins fragmentation functions as extracted from fits to the azimuthal asymmetries measured in semi-inclusive deep inelastic scattering and $e^{+}{e}^{-}$ annihilation processes. The description of the available data is extremely good, showing a clear general improvement with respect to the previous leading-order analysis. Predictions for unpolarized cross sections and single-spin asymmetries for ongoing and future experiments are also given.

Comments: 20 pages, 15 pdf figures. v2: few comments added in Section III-B.2, discussion in Section III-B.5 on the impact of the latest parametrizations extended, results unchanged. Matches published version