Sivers effect in Inelastic $J/\psi$ Photoproduction in $e{p}^{\uparrow }$ Collision in Color Octet Model

Abstract

The prediction of single-spin asymmetry in inelastic photoproduction of $J/\psi$ in $e{p}^{\uparrow }$ collision is presented. At next-to-leading order, the dominating process is photon-gluon fusion, $\gamma +g\to J/\psi +g$ for the production of $J/\psi$ in $e+p^{\uparrow }\to J/\psi +X$, which directly probes the gluon Sivers function. Using the non-relativistic QCD based color octet model, the color octet states $\text{leftidx}{}^{3}S{{}_1}^{(8)}$, $\text{leftidx}{}^{1}S{{}_0}^{(8)}$ and $\text{leftidx}{}^{3}P{{}_{J(0,1,2)}}^{(8)}$ contribution to $J/\psi$ production is calculated. Sizable asymmetry is estimated as a function of transverse momentum $P_T$ and energy fraction $z$ of $J/\psi$ in the range $0<P_T\le 1$ GeV and $0.3<z\le 0.9$. The unpolarized differential cross section of inelastic $J/\psi$ photoproduction is found to be in good agreement with H1 and ZEUS data.

Comments: Replaced with revised version; 33 pages, 10 figures, 3 tables