Exploring the gluon Sivers function in photon + jet production

We study transverse single spin asymmetries (TSSAs) in back-to-back photon plus jet production in the scattering of unpolarized beams of protons off a transversely polarized proton target as probes of Gluon Sivers Function (GSF). We provide estimates within the region where the imbalance ${\vec{q}}_{\perp }\equiv {\vec{p}}_{\gamma \perp }+{\vec{p}}_{J\perp }$ between the transverse momenta of the photon and the jet is much smaller than the average of the transverse momenta ${\vec{p}}_{\perp }\equiv \mid {\vec{p}}_{\gamma \perp }-{\vec{p}}_{J\perp }\mid \mathrm{/}2$ i.e. the back-to-back region. The presence of these two scales in the process makes it particularly suitable for applying transverse momentum dependent (TMD) factorization, in contrast to single-scale processes that rely on the generalized parton model approach. We present our preliminary results of the transverse single spin asymmetry for this process at $\sqrt{s}$ = 200 GeV.