Heavy quark distributions from the Color Dipole Picture

Abstract

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 ($x\le 10^{-2}$). 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 $2.5\le Q^2\le 2000{\mathrm{GeV}}^2$ 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.