Transverse single spin asymmetries in photon production

Transverse single spin asymmetries (SSA) in inclusive reactions are now considered to be directly related to the transverse momentum kT of the fundamental partons involved in the process. We find that the ideal probe to extract information on the gluon Sivers function is the transverse SSA of prompt photon production pp↑→γX, at large pT. The following related processes, pp↑→γ+jet+X, pp↑→γ∗+X→μ+μ−+X and p¯p↑→γ+X are also briefly discussed.