Transverse single-spin asymmetries in $\ell \,p^\uparrow \to h \,X$ within a TMD approach: Role of quasireal photon exchange

TL;DR

This paper updates the analysis of transverse single-spin asymmetries in lepton-proton collisions using a TMD approach, incorporating quasireal photon contributions, and achieves excellent agreement with experimental data.

Contribution

It introduces a unified TMD framework including quasireal photons for analyzing spin asymmetries, improving upon previous leading-order models.

Findings

Excellent agreement with existing data

Predictions for future experiments provided

Enhanced understanding of quasireal photon effects

Abstract

We present an updated study of transverse single-spin asymmetries for the inclusive large-$P_T$ processes $\ell \, p^\uparrow \to h\, X$ and $\ell\, p^\uparrow \to {\rm jet}\,X$, within a transverse momentum-dependent approach, including the contribution of quasireal (Weizs\"acker-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.