Matched predictions for Higgs production via heavy-quark loops in the SM and beyond

TL;DR

This work presents a fully exclusive simulation of Higgs production via gluon fusion that retains the exact heavy-quark loop dependence for h+0,1,2 partons and couples to parton showers using k_T-MLM and shower-k_T matching. By generating events in the HEFT and reweighting them with full one-loop amplitudes, the authors incorporate precise loop effects while maintaining feasible event generation and normalization to NNLO cross sections. In the Standard Model, loop effects are generally mild across most observables, with notable impact only at high Higgs p_T, whereas in b-philic scenarios bottom-quark loops dramatically alter kinematics and require exact treatment; tree-level bb -> h is also incorporated via five-flavor matching to capture dominant production channels. The approach provides a robust, general framework for loop-induced processes and improves the fidelity of exclusive predictions for Higgs production, with potential extension to other loop-driven phenomena and future automation in MadGraph/MadLoop.

Abstract

The main Higgs production channel at hadron colliders is gluon fusion via heavy-quark loops. We present the results of a fully exclusive simulation of gluon fusion Higgs production based on the matrix elements for h + 0, 1, 2 partons including full heavy-quark loop dependence, matched to a parton shower. We consider a Higgs with standard model couplings as well as models where the Higgs has enhanced couplings to bottom quarks (b-philic). We study the most relevant kinematic distributions, such as jet and Higgs pT spectra and find that matched samples provide an accurate description of the final state. For the SM Higgs, we confirm the excellent accuracy of the large heavy-quark-mass approximation also in differential distributions over all phase space, with significant effects arising only at large pT . For a b-philic Higgs however, the loops have a dramatic impact on the kinematics of the Higgs as well as of the jets and need to be accounted for exactly to achieve reliable event simulations.

Figures (5)

• Figure 1: SM Higgs $p_T$ distributions for $m_h=140$ GeV in gluon fusion production at the Tevatron. Results in the HEFT and with full loop dependence (LOOP) are compared to the default Pythia implementation (which accounts for $2\to2$ matrix element corrections) and to the NNLO+NNLL results as obtained by HqT Bozzi:2005wkdeFlorian:2011xf. Curves normalized to the corresponding total cross sections of Table \ref{['tab:xsec']}.
• Figure 2: SM Higgs $p_T$ distributions for $m_h=140$ GeV and $m_h=500$ GeV in gluon fusion production at 7 TeV LHC. In the upper plot results in the HEFT and with full loop dependence (LOOP) are compared over a large range of $p_T$ values to the default Pythia implementation, which accounts for $2\to2$ matrix element corrections. In the lower plot the low-$p_T$ range is compared to the NNLO+NNLL results as obtained by HqT Bozzi:2005wkdeFlorian:2011xf. Curves normalized to the corresponding total cross sections of Table \ref{['tab:xsec']}.
• Figure 3: Jet $p_T$ distributions for associated jets in gluon fusion production of $m_h=140$ GeV and $m_h=500$ GeV Higgs bosons at 7 TeV LHC.
• Figure 4: $b$-philic Higgs $p_T$ distribution a the Tevatron and the LHC with $m_h=140$ GeV. Results in the HEFT approximation (red curve) and with full loop dependence (green) are shown. Spectrum of Higgs produced via $b\bar{b}$ fusion in the five flavor scheme is also shown. All samples are matrix-element matched with up to two partons in the final state. Curves normalized to the corresponding total cross sections of Table \ref{['tab:xsec']}.
• Figure 5: Jet rates for $b$-philic Higgs production (where only the coupling to the bottom quark is included). $m_h=140$ GeV at the Tevatron and LHC ($\sqrt{s}=7$ TeV).