Single spin asymmetries in l p --> h X processes: a test of factorization
M. Anselmino, M. Boglione, U. D'Alesio, S. Melis, F. Murgia, A. Prokudin
TL;DR
This work assesses the viability of TMD factorization in hadronic processes with a single large scale by predicting transverse single-spin asymmetries in lepton–proton collisions that produce a high-$P_T$ hadron or jet. The authors compute $A_N$ within a TMD framework using SIDIS-extracted Sivers and Collins functions, finding that the Sivers effect largely dominates while Collins contributions are typically small. Predictions for HERMES, COMPASS, JLab, and ENC show potentially sizable $A_N$ for pion production at certain kinematics, whereas jet production offers a cleaner, albeit smaller, signal of the Sivers function. A measured $A_N$ in these channels would provide a direct test of TMD factorization in one-scale processes and inform the understanding of SSAs in hadronic collisions like $p p^{\uparrow} \to hX$.
Abstract
Predictions for the transverse single spin asymmetry (SSA), A_N, are given for the inclusive processes l p(transv. pol.) --> h X and l p(transv. pol.) --> jet + X, which could be measured in operating or future experiments. These estimates are based on the Sivers distributions and the Collins fragmentation functions which fit the azimuthal asymmetries measured in semi-inclusive deep inelastic scattering (SIDIS) processes (l p(transv. pol.) --> l' h X). The factorization in terms of transverse momentum dependent distribution and fragmentation functions (TMD factorization) - which supplies the theoretical framework in which SIDIS azimuthal asymmetries are analyzed - is assumed to hold also for the l p --> h X inclusive process at large P_T. A measurement of A_N would then provide a direct test of the validity of the TMD factorization in this case and would have important consequences for the study and understanding of SSAs in p p(transv. pol.) --> h X processes.