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 \({\textbf {q}}_{\perp } \equiv {\textbf {p}}_{\gamma \perp } + {\textbf {p}}_{J\perp }\) between the transverse momenta of the photon and the jet is much smaller than the average of the transverse momenta \({\textbf {p}}_{\perp } \equiv |{\textbf {p}}_{\gamma \perp } - {\textbf {p}}_{J\perp } |/ 2\) 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 \(\sqrt{s} = 200\;\textrm{GeV}\) .