Fig. \[fig:foto-part\]. This distribution is considered as a non-integrated distribution function regarding the coupling of the gluons to the proton through a gluon ladder described by the BFKL equation [@KMR-CanThe]. Moreover, the diffractive Higgs production is assumed to be an elastic process, where the momenta of the gluons are much smaller than the other kinematical variables under consideration. For a realistic description of the process, the partonic distribution is assumed to be a non-diagonal distribution, to express a more general situation, such that the proton loses a small fraction of its momentum during the collision. The matrix considered for the parton distribution in the proton is not diagonal, which means that the proton vertex has non-zero momentum transfer [@off-diag]. Thus, the following replacement is performed to describe the $\gamma p$ interaction $$\begin{aligned}
\frac{\alpha_{s} \, C_{F}}{\pi} \;\; \longrightarrow \;\; f_{g}(x,\boldsymbol{k}^{2}) = {\cal{K}} \left( \frac{\partial [xg(x,\boldsymbol{k}^{2})]}{\partial \ell n \, \boldsymbol{k}^{2}} \right)\end{aligned}$$ where $f_{g}(x,\boldsymbol{k}^{2})$ is the non-diagonal gluon distribution function in the proton evolved by the BFKL equation. The non-diagonality of the distribution can be approximated by a multiplicative factor ${\cal{K}}$, which possesses a Gaussian shape [@shuvaevetal] $$\begin{aligned}
{\cal{K}} = (1.2)\, \textrm{exp}(-B\boldsymbol{p}^{2}/2),\end{aligned}$$ with $B$ being the impact parameter, assumed to be $B = 