Gluon-initiated associated production boosts Higgs physics

TL;DR

The paper addresses the overlooked but potentially sizable gluon-initiated contribution to associated Higgs production in boosted $hZ$ events. By computing $gg\to hZ$ with full mass and coupling dependencies and analyzing boosted selection techniques, it demonstrates that differential distributions cannot be captured by simple rescalings of quark-initiated rates and that the cross sections depend sensitively on the Higgs-top coupling $c_t$ and its sign. The results show that boosted analyses are particularly sensitive to $c_t$ and can alter interpretations of SM Higgs rates as well as constraints in beyond-the-Standard-Model scenarios such as Type II 2HDMs and SUSY. The study argues for incorporating the gluon-initiated component into future LHC analyses to avoid misestimations and to fully exploit the discovery potential in Higgs coupling fits at high luminosity.

Abstract

Analyses of boosted Higgs bosons from associated production comprise some of the main search channels for the Higgs boson at the LHC. The gluon-initiated $gg\to hZ$ subprocess has largely been ignored in phenomenological analyses of boosted associated production although this contribution is sizable as the $p_T$ spectrum for this process is maximised in the boosted regime due to the top quark loop threshold. In this paper, we discuss this contribution to boosted $pp\to hZ$ analyses in detail. We find there are previously overlooked modifications of Standard Model Higgs rates at the LHC which depend on the $p_T$ cuts applied and can be significant. There are also important consequences for physics beyond the Standard Model as the $gg\to hZ$ process introduces significant dependence on the magnitude and sign of the Higgs-top quark coupling $c_t$, which is overlooked if it is assumed that associated production depends only on the Higgs-$Z$ boson coupling as $c_V^2$. This new dependence on $c_t$ impacts interpretations of Higgs rates in the contexts of Supersymmetry, Two Higgs Doublet Models, and general scenarios with modified couplings. We suggest that these effects be included in current and future LHC boosted Higgs analyses.

Figures (7)

• Figure 1: Feynman diagram topologies contributing to $gg\to hZ$ at leading order in general gauge.
• Figure 2: Invariant $hZ$ mass $m_{hZ}$ (left) and $p_T$ spectra (right) for $pp\to hZ$ production at $\sqrt{s}=14$ TeV. The gluon-initiated and quark-initiated contributions are shown for comparison We also plot contributions from box and triangle diagrams to demonstrate the cancellation between the two in the sum.
• Figure 3:
• Figure 4: Invariant truth-level $hZ$ mass for $pp\to (h\to \overline b b) (Z\to \mu^+\mu^-,e^+e^-)$ production in the SM at $\sqrt{s}=14$ TeV. These results are a direct reflection of Fig. \ref{['fig:ptsm']} after the analysis cuts and the reconstruction have been applied. NLO correction factors as reported in Refs. asshzggasshzqcd have been included to reflect the proper signal composition.
• Figure 5: Parameter dependence of the inclusive associated production cross section relative to the SM result at 14 TeV after including $K$-factors and with the gluon-initiated contribution included (solid black) and omitted (dashed red). The result which omits the gluon-initiated contribution is a good approximation to the full result in this case.