Dmitri Diakonov, M. G. Ryskin, A. G. Shuvaev
C-parity-even charmonia eta_c and chi_c with spin 0 and 2 are produced via two-gluon fusion. The expected cross section of the inclusive production of these charmonia at the LHC, times the branching ratios of convenient decays, is up to several hundred nanobarn per unit rapidity. Measuring the production of charmonia as function of rapidity will allow to determine the gluon distribution function in nucleons in a very broad range of the Bjorken x from x ~ 10^(-2) where it is already known, down to x ~ 10^(-6) where it is totally unknown. The scale of the gluon distribution found from such a measurement turns out to be rather low, Q^2 ~ 2.5 - 3 GeV^2. We evaluate this scale by studying the next-to-leading-order production matrix elements.
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http://arxiv.org/abs/1211.1578
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