Abstract
We calculate the Sivers and cos 2phi azimuthal asymmetries in J/psi 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/psi 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 2phi asymmetry is sizable and probes the linearly polarized gluon distribution in an unpolarized proton.
Highlights
Among the single spin asymmetries the Sivers asymmetry is one of the most important and well studied asymmetry, both theoretically and experimentally
The Sivers asymmetry with respect to PhT obtained from the SIDIS1 parameters is higher at JLab and HERMES whereas the Single spin asymmetry (SSA) obtained from the BV-b set parameters is dominant at COMPASS and EIC experiments
The J/ψ production process gives direct access to the gluon Sivers function at leading order through the channel γ ∗g → cc
Summary
Among the single spin asymmetries the Sivers asymmetry is one of the most important and well studied asymmetry, both theoretically and experimentally. The cross section is described in terms of a product of a perturbative part where the initial state partons form a ccpair having a definite color and total angular momentum quantum numbers and a nonperturbative matrix element through which the ccpair forms J/ψ. These matrix elements are obtained by fitting data. The effect of the TMD evolution on the Sivers asymmetry in the J/ψ production in the COM has been studied. H⊥1 q has been extracted in [60–62] from the cos 2φ asymmetry SIDIS data assuming a relation with the Sivers function.
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