the data, thus we do not constrain ourselves to the back-to-back dijet region analyzed in [@Dominguez:2011wm]. Rather, we shall use the HEF factorization for dijet production. Since this approach is an extension of the CCH formalism, we shall now briefly recall the latter and the required extensions to obtain HEF for dijets. For a direct derivation from CGC approach see [@Kotko:2015ura].

In the CCH high energy factorization, one considers the heavy quark pair produced via the tree-level hard sub-process $g^{*}\left(k_{A}\right)g^{*}\left(k_{B}\right)\rightarrow Q\overline{Q}$ in the axial gauge. The initial state gluons are off-shell and have the momenta of the form $k_{A}=x_A\, p_{A}+k_{TA}$ and $k_{B}=x_B\, p_{B}+k_{TB}$, where $p_{A}$, $p_{B}$ are the momenta of the incoming hadrons and $p_{A}\cdot k_{TA}=p_{B}\cdot k_{TB}=0$. This particular form of the exchanged momenta is a result of the imposed high energy limit. The off-shell gluons have “polarization vectors” that are $p_{A}$ and $p_{B}$ respectively. Thanks to this kinematics the sub-process given by ordinary Feynman diagrams is gauge invariant despite its off-shellness. In CCH approach the factorization formula for heavy quark production reads (see Fig. \[fig:HEF\]A) $$\begin{gathered}
d\sigma_{AB\rightarrow Q\overline{Q}}=\int d^{2}k_{T A}\int\frac{dx_{A}}{x_{A}}\,\int d^{2}k_{T B}\int\frac{dx_{B}}{x_{B}}\,\\
\mathcal{F}_{g^{*}/A}\left(x_{A},k_{T A}\right)\,\mathcal{F}_{g^{*}/B}\left(x_{B},k_{T B}\right)\, d\hat{\sigma}_{g^{*}g^{*}\rightarrow Q\overline{Q}}\left(x_{A},x_{B},k_{T A},k_{T B}\right),\label{eq:HEN_fact_1}\end{gathered}$$ where $d\hat{\sigma}_{g^{*}g^{*}\rightarrow Q\overline{Q}}$ is the partonic cross section build up 