Gluon Sivers function and transverse single spin asymmetries in e plus p↑ → γ plus X

We present estimates of transverse single-spin asymmetry in prompt photon production in the scattering of low virtuality photons off a polarized proton target and discuss the possibility of using this as a probe to get information about the gluon Sivers function (GSF). Using a generalized parton model (GPM) framework, we estimate the asymmetries at electron-ion collider energy (root s = 140 GeV) taking into account both direct and resolved photon processes and find that the dominant contribution, up to 10%, comes from quark Sivers function (QSF) while the contribution from GSF is found to be up to 2%. However, upon taking into account the effects of the process-dependent initial and final state interactions through the color-gauge invariant generalized parton model approach we find that the situation is significantly changed, with near zero contributions from the QSFs and up to a 1% level contribution from the f-type GSF. Our results indicate that this process may be useful for distinguishing between GPM and color-gauge invariant generalized parton models and can be used as a good probe of f-type GSF.

Automated summary

This study discusses the estimates of transverse single-spin asymmetry in prompt photon production in the scattering of low virtuality photons off a polarized proton target, and the possibility of using this as a probe to obtain information about the gluon Sivers function (GSF). Using a generalized parton model (GPM) framework, it was found that the dominant contribution comes from quark Sivers function (QSF), but the situation changes significantly when considering the effects of initial and final state interactions through the color-gauge invariant generalized parton model approach.