Elastic double diffractive production of axial-vector chi_c(1⁺⁺) mesons and the Landau-Yang theorem

We discuss exclusive elastic double diffractive axial-vector \chi_c(1^{+}) meson production in proton-antiproton collisions at the Tevatron. The amplitude for the process is derived within the k_t-factorisation approach with unintegrated gluon distribution functions (UGDFs). We show that the famous Landau-Yang theorem is not applicable in the case of off-shell gluons. Differential cross sections for different UGDFs are calculated. We compare exclusive production of \chi_c(1^+) and \chi_c(0^+). The contribution of \chi_c(1^+) to the J/\Psi + \gamma channel is smaller than that of the \chi_c(0^+) decay, but not negligible and can be measured. The numerical value of the ratio of the both contributions is almost independent of UGDFs modeling.