Very low x gluon density determined by LHCb exclusive J/ψ data

The low x behavior of the gluon density xg(x, mu(2)) at scale mu(2) = 2.4 GeV2 is determined using exclusive J/psi production data from HERA and LHCb within the framework of collinear factorization at next-to-leading order (NLO). It is shown that in the interval 3 x 10(-6) < x < 10(-3) the gluon distribution function grows as xg(x, mu(2)) proportional to x(-lambda) with lambda = 0.135 +/- 0.006. The impact this experimental data will have for the global parton distribution function (PDF) analyses in this low x domain is quantified. No indication in favour of parton density saturation is observed.