D and B-meson production using kt-factorization calculations in a variable-flavor-number scheme

TL;DR

This work provides the first consistent kt-factorization calculations for heavy-quark (D and B meson) production using a GM-VFNS at $\mathcal{O}(\alpha_s^2)$, including all relevant $2\to 2$ processes and a treatment of the $2\to 1$ contribution. It develops and employs Watt-Martin-Ryskin unintegrated PDFs built from CT14 inputs, couples them to the Ka Tie event generator, and validates the approach against ALICE and LHCb data across central and forward rapidities, with good overall agreement and controlled scale uncertainties. The results highlight the critical importance of scheme consistency between uPDFs and the perturbative cross sections, and reveal limitations at very forward rapidity that motivate data-driven uPDFs or improved modeling. The study also situates kt-factorization results relative to other approaches, showing improvements when the GM-VFNS framework is applied coherently and suggesting avenues for extending the formalism to jet-related observables.

Abstract

Within the framework of $k_t$-factorization, we compute the differential cross section for the production of $B$ and $D$ mesons, using a general-mass variable-flavor-number scheme. Our calculations include all relevant $2\to 2$ processes. We explain how to include the $2\to 1$ process in our calculations, but argue this is not (numerically) relevant at moderate transverse momentum due to its cancellation with the subtraction term. We apply this formalism to $pp$ collisions and compare our results with ALICE and LHCb data at central and forward rapidity.

Figures (18)

• Figure 1: Comparison of our SO WMR uPDFs (full lines) with the PB (dotted lines) and AO WMR (dashed lines) uPDFs.
• Figure 2: Comparison of CT14 LO parton distributions (full lines) at $x=0.001$ with the integrated uPDFs (dashed lines), see Eq. (\ref{['undens']}).
• Figure 3: Same as Fig. \ref{['unpdf1']} for $x=0.01$.
• Figure 4: Leading order $k_t$-factorization calculations, obtained in a GM-VFNS, compared to ALICE data al7D2017 for $D^0$ mesons. The line shows the central value of our calculations and the band corresponds to the factorization scale uncertainty.
• Figure 5: Same as Fig. \ref{['d07']} for $D^+$ mesons.