Top-Yukawa contributions to bbH production at the LHC

TL;DR

This work provides a first complete NLO QCD analysis of $b\bar{b}H$ production in the SM, decomposing the cross section into $y_b^2$, $y_t^2$, and $y_b y_t$ components within the 4-flavour scheme. It uses the HEFT to evaluate top-loop induced $y_t^2$ corrections, with a Born-improved BI-HEFT approach to incorporate finite-$m_t$ effects, and demonstrates that $y_t^2$ contributions significantly boost the inclusive rate and often dominate the cross section. The authors map out discriminating observables and cuts that enhance sensitivity to the bottom Yukawa coupling, showing that low Higgs transverse momentum and veto strategies on $bb$ jets can increase the relative $y_b^2$ fraction, albeit with reduced statistics. They also study $g\to b\bar{b}$ splittings via the $z_g(b_1)$ observable, highlighting how top-loop driven configurations differ from bottom-loop ones and informing how parton-shower or fragmentation approaches can better capture the associated dynamics. Overall, the results imply a sizable, top-loop-dominated $b\bar{b}H$ rate at the LHC and establish concrete strategies for isolating the bottom Yukawa signal amidst dominant top-loop contributions, with clear paths forward toward parton-shower matching and broader phenomenological implications.

Abstract

We study the production of a Higgs boson in association with bottom quarks ($b\bar{b}H$) in hadronic collisions at the LHC, including the different contributions stemming from terms proportional to the top-quark Yukawa coupling ($y_t^2$), to the bottom-quark one ($y_b^2$), and to their interference ($y_b y_t$). Our results are accurate to next-to-leading order in QCD, employ the four-flavour scheme and the (Born-improved) heavy-top quark approximation. We find that next-to-leading order corrections to the $y_t^2$ component are sizable, making it the dominant production mechanism for associated $b\bar{b}H$ production in the Standard Model and increasing its inclusive rate by almost a factor of two. By studying final-state distributions of the various contributions, we identify observables and selection cuts that can be used to select the various components and to improve the experimental sensitivity of $b\bar{b}H$ production on the bottom-quark Yukawa coupling.

Figures (14)

• Figure 1: Examples of Feynman diagrams for $b \bar{b} H$ production at LO and at NLO, which contain virtual and real diagrams proportional to $y_b$, and virtual diagrams with a top loop proportional to $y_t$. The corresponding amplitudes are named ${\cal A}_b^{(0)}$, ${\cal A}_b^{(1V)}$, ${\cal A}_b^{(1R)}$ and ${\cal A}_t^{(0)}$.
• Figure 2: Examples of virtual, ${\cal A}_t^{(1V)}$, and real emission, ${\cal A}_t^{(1R)}$, diagrams contributing to associated $b \bar{b} H$ production at ${\cal O}\space\left(y_t^2{}\,\alpha_s^5\right)$, and ${\cal O}\space\left(y_b\, y_t{}\,\alpha_s^4\right)$ through their interference with ${\cal A}_b^{(0)}$ and ${\cal A}_b^{(1R)}$.
• Figure 3: Examples of Born-level, virtual and real-emission diagrams for the $y_t^2$ contribution to $b \bar{b} H$ production in the heavy-top quark approximation.
• Figure 4: Comparison of LO predictions in the SM and the HEFT for various observables: the transverse-momentum of the Higgs boson (\ref{['fig:approx-pth']}), of the leading (\ref{['fig:approx-ptb1']}), and of the subleading $b$ jet (\ref{['fig:approx-ptb2']}), the rapidity of the Higgs boson (\ref{['fig:approx-etah']}), the invariant mass of the $b$-jet pair (\ref{['fig:approx-mbb']}), and their distance in the $\eta$--$\phi$ plane (\ref{['fig:approx-drbb']}); the lower insets show the ratio of the two predictions.
• Figure 5: Distributions in the transverse momentum of the Higgs boson (\ref{['fig:pt-h']}) and of the hardest $b$ jet (\ref{['fig:pt-b1']}). See the text for details.