We calculate the Sivers and cos 2φ azimuthal asymmetries in J/ψ production in the polarized and unpolarized semi-inclusive ep collision, respectively, using the formalism based on the transverse momentum-dependent parton distributions (TMDs). The non-relativistic QCD-based color octet model is employed in calculating the J/ψ production rate. The Sivers asymmetry in this process directly probes the gluon Sivers function. The estimated Sivers asymmetry at z = 1 is negative, which is in good agreement with the COMPASS data. The effect of TMD evolution on the Sivers asymmetry is also investigated. The cos 2φ asymmetry is sizable and probes the linearly polarized gluon distribution in an unpolarized proton.

No abstract

The prediction of single-spin asymmetry in inelastic photoproduction of J=ψ in ep ↑ collision is presented. At next-to-leading order, the dominating process is photon-gluon fusion, γ þ g → J=ψ þ g for the production of J=ψ in e þ p ↑ → J=ψ þ X, which directly probes the gluon Sivers function.Using the nonrelativistic QCD based color octet model, the color octet states 3 S contribution to J=ψ production is calculated. Sizable asymmetry is estimated as a function of transverse momentum P T and energy fraction z of J=ψ in the range 0 < P T ≤ 1 GeV and 0.3 < z ≤ 0.9. The unpolarized differential cross section of inelastic J=ψ photoproduction is found to be in good agreement with H1 and ZEUS data.

We calculate the transverse single-spin asymmetry (SSA) for J/ψ 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-PT 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. * Electronic address: umberto.dalesio@ca.infn.it † Electronic address: francesco.murgia@ca.infn.it ‡ Electronic address: cristian.pisano@ca.infn.it § Electronic address: rajesh.sangem@ca.infn.it

We study the possibility to probe the unpolarized and linearly polarized transverse momentumdependent gluon distributions in unpolarized pp collision in charmonium and bottomonium production, employing non-relativistic QCD (NRQCD) based color octet model within transverse momentum dependent (TMD) factorization framework. The transverse momentum (p T ) and rapidity distributions of J/ψ and Υ(1S) at LHCb, RHIC and AFTER energies are estimated. Significant modulations in transverse momentum spectrum of quarkonium in the low p T region is obtained when contributions of linearly polarized gluons inside an unpolarized proton are taken into account. The results of quarkonium production in color octet model and color evaporation model are compared.