Prompt charmonia production and polarization at the LHC in the NRQCD with kT-factorization. III. J/Ψ meson

In the framework of the k(T)-factorization approach, the production and polarization of prompt J/Psi mesons at the LHC energies is studied. Our consideration is based on the nonrelativistic QCD formalism for bound states and off-shell amplitudes for hard partonic subprocesses. Both the direct production mechanism and feed-down contributions from chi(c) and Psi(2S) decays are taken into account. The transverse momentum dependent (or unintegrated) gluon densities in a proton were derived from Ciafaloni-Catani-Fiorani-Marchesini evolution equation or, alternatively, were chosen in accordance with Kimber-Martin-Ryskin prescription. The nonperturbative color-octet matrix elements were first deduced from the fits to the latest CMS data on J/Psi transverse momentum distributions and then applied to describe the ATLAS and LHCb data on J/Psi production and polarization at root s = 7, 8 and 13 TeV. We perform an estimation of polarization parameters lambda(theta), lambda(phi), and lambda(theta phi) which determine J/Psi spin density matrix and demonstrate that treating the soft gluon emission as a series of explicit color-electric dipole transitions within NRQCD leads to unpolarized J/Psi production at high transverse momenta, that is in qualitative agreement with the LHC data.