Quasi-real photon contribution to AN in ℓp↑ →φ X within a TMD approach

D'Alesio U.;Flore C.;Murgia F.

2016-01-01

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Abstract

Within a TMD approach we discuss the impact of quasi-real (Weizsäcker-Williams) photon contribution to the transverse single-spin asymmetry, AN, for the inclusive process ℓp↑ → φ X. This study extends a previous one where only the leading-order contribution was taken into account. Predictions are obtained adopting the Sivers and transversity distributions and the Collins fragmentation functions as extracted from fits to the azimuthal asymmetries measured in semiinclusive deep inelastic scattering and e+e-annihilation processes. The description of the available data is very good, showing a clear general improvement with respect to the previous analysis (already quite promising). This result represents a further step towards a unified TMD treatment of SSAs in ℓp↑ → ℓ'hX and ℓp↑ → hX processes.