QCD leading order study of the J/Ψ leptoproduction at HERA within the nonrelativistic QCD framework

As indicated in our previous paper (Zhang and Sun in Phys. Rev. D 96: 034002, 2017), the existing literature studying the J/Psi production in deeply inelastic scattering (DIS) in collinear factorisation is on the basis of a formalism that will lead to wrong results when the ranges of the transverse momentum or the rapidity of the J/Psi in the laboratory frame do not cover all values possible for them. In this paper, we present the renewed results for the J/Psi production in DIS at HERA within the nonrelativistic QCD framework at QCD leading order (LO). Three different sets of the longdistance matrix elements are employed for comparison. The predictions via the colour-singlet (CS) model at QCD LO are generally below the experimental data especially in the regions where perturbation theory are expected to work well, while the colour-octet contributions are of the same order of magnitude as the CS ones, however, in general make the agreement between theory and experiment better.