Sivers effect in Drell-Yan processes

Abstract

The Sivers distributions recently extracted from semi-inclusive deep inelastic scattering data [1] are used to compute estimates for Sivers asymmetries in Drell-Yan processes which are being planned at several facilities (RHIC, COMPASS, J-PARC, PAX, PANDA, NICA (JINR) and SPASCHARM (IHEP)). Most of these asymmetries turn out to be large and could allow a clear test of the predicted sign change of the Sivers distributions when active in SIDIS and Drell-Yan processes. This is regarded as a fundamental test of our understanding, within QCD and the factorization scheme, of single spin asymmetries.

Revealing transversity GPDs through the photoproduction of a photon and aρmeson

“…There are rather huge uncertainties for these cross-sections, mainly of course because of our poor knowledge of chiral-odd GPDs. One of the main uncertainties is due to the fact that the transversity PDFs [12], on which we rely to build our model for transversity GPDs, are themselves not very constrained by existing data on semi-inclusive deep inelastic scattering.…”

Transverse single-spin asymmetries inp↑p→γXfrom quark-gluon-quark correlations in the proton

“…For the unpolarized distributions we use the GRV98 fit [71], which were also used by Refs. [64][65][66]69] for the other aforementioned non-perturbative inputs that enter. All parton correlation functions are evaluated at the scale q T with leading order evolution of the collinear functions.…”

“…4-6, in general the chiral-odd piece is negligible. We have checked that this is a robust statement by changing parameters in both the Boer-Mulders function from [64] (including looking at both Fit 1 and Fit 2) and the transversity function from [69] within their error ranges. In all cases, we found the chiral-odd piece is roughly four orders of magnitude smaller than the total asymmetry (in the x F -range where A γ N is nonzero).…”

“…Therefore, we believe that the ansatz in (30) is suitable to obtain the maximum possible chiral-even SFP contribution to A γ N . The transversity function is taken from the extraction in [69], with the antiquarks set to saturate the Soffer bound [70]. For the unpolarized distributions we use the GRV98 fit [71], which were also used by Refs.…”

ANin inclusive lepton-proton collisions: TMD and twist-3 approaches

“…On the other hand one could assume TMD factorization and then compute the asymmetry using TMD functions, as done in [1,42,43]. Assuming the validity of the TMD factorisation scheme for the process p → h X in which the only large scale detected is the transverse momentum P T of the final hadron in the proton-lepton c.m.…”