  The current uncertainty on the gluon density extracted from the global parton
analysis is large in the kinematical range of small values of the Bjorken - $x$
variable and low values of the hard scale $Q^2$. An alternative to reduces this
uncertainty is the analysis of the exclusive vector meson photoproduction in
photon - hadron and hadron - hadron collisions. This process offers a unique
opportunity to constrain the gluon density of the proton, since its cross
section is proportional to the gluon density squared. In this paper we consider
current parametrizations for the gluon distribution and estimate the exclusive
vector meson photoproduction cross section at HERA and LHC using the leading
logarithmic formalism. We perform a fit of the normalization of the $\gamma h$
cross section and the value of the hard scale for the process and demonstrate
that the current LHCb experimental data are better described by models that
assume a slow increasing of the gluon distribution at small - $x$ and low
$Q^2$.
