Production of forward heavy-flavor dijets at the LHCb within the kT -factorization approach

We calculate differential cross sections for cc¯- and bb¯-dijet production in pp scattering at s=13 TeV in the kT-factorization and hybrid approaches with different unintegrated parton distribution functions (uPDFs). We present distributions in the transverse momentum and pseudorapidity of the leading jet, the rapidity difference between the jets and the dijet invariant mass. Our results are compared to recent LHCb data on forward production of heavy-flavor dijets, measured recently for the first time individually for both charm and bottom flavors. We find that an agreement between the predictions and the data within the full kT factorization is strongly related to the modeling of the large-x behavior of the gluon uPDFs, which is usually not well constrained. The problem may be avoided following the hybrid-factorization approach. Then, we obtain a good description of the measured distributions with the parton-branching, Kimber-Martin-Ryskin, Kutak-Sapeta, and Jung setA0 models for the gluon uPDF. We also calculate differential distributions for the ratio of the cc¯ and bb¯ cross sections. In all cases we obtain a ratio close to 1, which is caused by the condition on the minimal jet transverse momentum (pTjet>20 GeV) introduced in the experiment, that makes the role of the heavy-quark mass almost negligible. The LHCb experimental ratio seems a bit larger than the theoretical predictions. We discuss potentially important for the ratio effect of c- or b-quark gluon radiative corrections related to emission outside of the jet cone. The found effect seems rather small. A more refined calculation requires full simulation of c and b jets, which goes beyond of the scope of this paper.