Reformulation of the twist-3 gluon Sivers effect toward an application to heavy quarkonium production

In this paper, we propose a new calculation method for the twist-3 gluon Sivers effect within the collinear factorization approach. The method called pole calculation has been used to derive the cross section formula for the single transverse-spin asymmetry as a standard method. We point out that we encounter a problem when we try to apply the pole calculation to the single transverse-spin asymmetry in the heavy quarkonium production whose hadronization mechanism is described by nonrelativistic QCD framework. We show that the new calculation method solves this problem and successfully reproduces known results derived by the pole calculation. Our new method extends the applicability of the twist-3 calculation technique to heavy quarkonium productions that are ideal observables for the investigation of the gluon