Heavy quark distributions from the Color Dipole Picture

To study charm -quark pair production processes, we utilized the color dipole picture gluon distribution function in a collinear generalized double asymptotic scaling approach at small Bjorken $x$ values ($x{\leq}10^{-2}$). Our results show good agreement with the latest HERA experimental data for reduced cross sections $\sigma_{\mathrm{red}}^{c\overline{c}} (W^2,Q^2)$ across a wide range of $x$ and $Q^2$ values, yielding an effective pomeron intercept. A Hard pomeron intercept with the coefficient $C_{2}=0.29$ in the color dipole model provides comparable results at very low $x$ values ($x{<}10^{-3}$). We demonstrate that the experimental data from HERA in the region $2.5{\leq}Q^2{\leq}2000~\mathrm{GeV}^2$ confirms the symmetry between the saturation and color transparency regions in the scaling variable $\eta$, shifting towards the color transparency region when we incorporate the threshold mass production of $J/\psi$ meson in the color dipole picture.