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Relativistic corrections to η_c-pair production in high energy proton-proton collisions

On the basis of perturbative QCD and the relativistic quark model we calculate relativistic corrections to the double $η_c$ meson production in proton-proton interactions at LHC energies. Relativistic terms in the production amplitude connected with the relative motion of heavy quarks and the transformation law of the bound state wave functions to the reference frame of moving charmonia are taken into account. For the gluon and quark propagators entering the amplitude we use a truncated expansion in relative quark momenta up to the second order. Relativistic corrections to the quark bound state wave functions are considered by means of the Breit-like potential. It turns out that the examined effects decrease total nonrelativistic cross section more than two times and on 20 percents in the rapidity region of LHCb detector.