$$J/\psi $$ J / ψ production in polarized and unpolarized ep collision and Sivers and $$\cos 2\phi $$ cos 2 ϕ asymmetries

Abstract

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.

Single-spin asymmetry ofJ/ψproduction inp+p,p+Al, andAidala1, Akiba2, Alfred3 et al. 2018Phys. Rev. D211180View full textAdd to dashboardCite

“…For the TMD approach to be valid in the context of p þ p collisions, Q 2 must be large, in order to use perturbative QCD, while the transverse momentum must satisfy p T ≪ Q and not be much larger than the intrinsic, parton transverse momentum k T , so that effects of the latter remain visible [25]. One of the TMD PDFs, called the Sivers function [4], is widely used in describing the TSSA's that were observed in different processes [26][27][28][29][30]. The Sivers function, denoted by f ⊥ 1T ðx; k 2 ⊥ Þ, describes the distortion in the distribution of unpolarized partons with momentum fraction x and transverse momentum k ⊥ in a transversely polarized hadron.…”

Proper TMD factorization for quarkonia production: pp → ηc, b as a study case

“…All and all, quarkonium production seems the most promising way to probe gluon TMDs. Indeed, there has been a growing interest lately, with numerous proposals based on treelevel ansatzs for TMD factorization for quarkonium production [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] and even several next-to-leading-order (NLO) calculations [41][42][43][44].…”

Sivers effect in inelastic J/ψ photoproduction in ep↑ collision in color octet model

“…In photoproduction, the inelastic variable z can be measured in experiments using the Jacquet-Blondel method [39,40,42]. The LO photon-gluon fusion subprocess (γ þ g → J=ψ) contributes to elastic photoproduction at z ¼ 1 [20]. The process of a colorless exchanged particle between quasireal photon and proton, diffractive process, contributes to J=ψ production in the elastic region, i.e., z ≈ 1 and P T ≈ 0 GeV [52,53].…”

“…Heavy quarkonium production in ep [19][20][21][22][23] and pp [24,25] collision has been studied theoretically quite extensively for probing the gluon TMDs, in particular the GSF and linearly polarized gluon distribution [26,27]. This is because the heavy quarkonium is produced at leading order (LO) through photon-gluon fusion (ep) or two gluon fusion (pp) channel.…”

“…In our previous work [20], we calculated the Sivers asymmetry in J=ψ electroproduction at LO, which is a photon-gluon 2 → 1 process, in color octet model (COM). We showed that the calculated asymmetry at z ¼ 1 agrees within the error bar of the recent COMPASS [50] measurement.…”