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Precise modeling of gluon-splitting contributions to tt̄+heavy-flavor production

Establish a sufficiently precise theoretical and phenomenological understanding of gluon splitting into heavy quark pairs (g → bb̄ or g → cc̄) to enable accurate simulation-based predictions of the tt̄+heavy-flavor production rate in proton-proton collisions at √s = 13 TeV for reliable background estimation in associated VH searches for H → aa → 4b.

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Background

The analysis separates tt̄ background into light-flavor (LF) and heavy-flavor (HF) components based on additional particle-level jets matched to heavy hadrons. The tt̄+HF category is dominated by gluon splitting (g → cc̄ or g → bb̄), and its overall normalization is not taken from simulation but instead determined by a fit to data due to modeling limitations.

Accurate prediction of tt̄+HF rates is essential for constraining backgrounds in the VH, H → aa → 4b search. The paper explicitly notes the insufficiency of current understanding of gluon splitting to provide a well-predicted simulation rate for tt̄+HF.

References

In contrast to tt̄+LF events, the rate of tt̄+HF events is not well predicted by simulation because it is dominated by the gluon splitting process, which is not yet well understood to adequate precision.

— Search for the decay of the Higgs boson to a pair of light pseudoscalar bosons in the final state with four bottom quarks in proton-proton collisions at $\sqrt{s}$ = 13 TeV (2403.10341 - Collaboration, 15 Mar 2024) in Section 4.2 (Background modeling and control regions)