Abstract
We calculate the transverse single-spin asymmetry (SSA) for J/psi production in proton-proton collisions, within non-relativistic QCD, employing the transverse momentum dependent, generalized parton model, which includes both spin and intrinsic motion effects. In particular, we study the role of the color octet mechanism in accessing the gluon Sivers function. In doing that, we also show, within this approach, how the singularities coming from color octet terms in the low-P_T region can be handled, leading to finite cross sections. Predictions for both unpolarized cross sections and SSAs are given and compared against PHENIX data. Estimates for LHCb in the fixed target mode are also presented.
Highlights
While for the quark Sivers function the amount of information is certainly well consolidated, thanks to several experimental results and their phenomenological analyses, very little is known on its gluon counterpart [4]
In this paper we focus on single-spin asymmetry (SSA) for J/ψ production in pp collisions within the Generalized Parton Model (GPM) approach, studying in detail the role played by the color octet (CO) w.r.t. the color singlet (CS) mechanism within non-relativistic QCD (NRQCD), i.e. we exploit the contributions from the 3 S1(1,8), 1 S0(8) and 3 PJ(8) states
Concerning the access to the gluon Sivers function (GSF), we find that some CO contributions turn out to be relevant, in particular when looking at backward rapidities
Summary
While for the quark Sivers function the amount of information is certainly well consolidated, thanks to several experimental results and their phenomenological analyses, very little is known on its gluon counterpart [4]. In this paper we focus on SSAs for J/ψ production in pp collisions within the GPM approach, studying in detail the role played by the CO w.r.t. the CS mechanism within NRQCD, i.e. we exploit the contributions from the 3 S1(1,8), 1 S0(8) and 3 PJ(8) states. For completeness we will consider in some detail the differential cross section within the GPM approach, comparing our results with PHENIX data [41], in the moderate and low-PT (the transverse momentum of the J/ψ) region As it will be shown, the inclusion of intrinsic transverse momentum effects could play an important role in this context. We mention that the role of possible initial- and final-state interactions, and their interplay with the color octet mechanism, could open an interesting perspective in the study of SSAs within the CGI-GPM approach This ongoing analysis will be presented in a future publication.
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