  We investigate photo-production of vector mesons J/Psi and Upsilon measured
both at HERA and LHC, using 2 particular fits of inclusive unintegrated gluon
distributions, based on non-linear Balitsky-Kovchegov evolution (Kutak-Sapeta
gluon; KS) and next-to-leading order Balitsky-Fadin-Kuraev-Lipatov evolution
(Hentschinski-Sabio Vera-Salas gluon; HSS). We find that linear next-to-leading
order evolution can only describe production at highest energies, if
perturbative corrections are increased to unnaturally large values; rendering
this corrections to a perturbative size, the growth with energy is too strong
and the description fails. At the same time, the KS gluon, which we explore
both with and without non-linear corrections, requires the latter to achieve an
accurate description of the energy dependence of data. We interpret this
observation as a clear signal for the presence of high gluon densities in the
proton, characteristic for the onset of gluon saturation.
