Anomalous Higgs boson couplings in vector boson fusion at the CERN LHC

TL;DR

The paper develops and applies a dimension-6 effective Lagrangian framework to study anomalous HVV couplings in Higgs production via vector boson fusion at the LHC, implementing these effects in the VBFNLO program with NLO QCD accuracy for production and decay. By leveraging LEP constraints, it assesses the size of possible deviations from the Standard Model, finding that anomalous HWW couplings can noticeably enhance VBF cross sections, while Hγγ and HZγ decays can experience large width enhancements that affect signals. A key contribution is the proposal and analysis of a sign-sensitive azimuthal angle between the VBF tagging jets, Δφ_jj, which reveals interference between CP-even and CP-odd contributions and serves as a direct probe of CP violation in the Higgs sector. The work provides a practical tool and observables for LHC experiments to characterize the tensor structure of HVV couplings and CP properties, with implications extending to gluon-fusion scenarios as well.

Abstract

Deviations from SM expectations in the Higgs sector can be parameterized by an effective Lagrangian. The corresponding anomalous couplings have been implemented in a Monte Carlo program for Higgs production in vector boson fusion, at NLO QCD accuracy. It allows to study anomalous coupling effects for production and decay of the Higgs boson. We analyze deviations allowed by LEP data and study a new azimuthal angle variable which directly measures the interference between CP-even, CP-odd and SM couplings.

Figures (5)

• Figure 1: Feynman graphs contributing to $\bar{q}Q\to \bar{q}QH$ at (a) tree level and (b) including virtual corrections to the upper quark line. The momentum labels and Lorentz indices for the internal weak bosons correspond to the vertex function of Eq. (\ref{['eq:vertex']}).
• Figure 2: Production cross section of a Higgs Boson with anomalous couplings in addition to the SM $HVV$ interactions. Left: The upper bounds for $g_{H\gamma\gamma}$ and $g_{HZ\gamma}^{(2)}$ given in Table \ref{['tab:directbounds']} and the upper 95% CL bounds for $d$ and $d_B$, given by the L3 collaboration, are used. Right: The upper bound for $d$ is used for the different couplings.
• Figure 3: Normalized azimuthal angle correlations of the two tagging jets in VBF as in Ref. Plehn:2001nj for a Higgs mass of 120 GeV and $d$ = 0.18 or, respectively, $\tilde{d}$ = 0.18. Left: Purely CP-even, CP-odd or SM couplings. Right: CP-even and CP-odd couplings of the same size.
• Figure 4: Normalized distribution of the azimuthal angle $\Delta\phi_{jj}$ defined in Eq. (\ref{['eq:phijj']}) for a Higgs mass of 120 GeV and a mixed CP scenario ($d$ = $\tilde{d}$ = 0.18, red solid curve), a CP-even anomalous coupling ($d$ = 0.18, $\tilde{d}$ = 0, green dashed curve), a CP-odd coupling ($d$ = 0, $\tilde{d}$ = 0.18, blue dotted curve) and the SM case (purple narrow dotted line).
• Figure 5: Normalized distribution of the azimuthal angle for a Higgs mass of 120 GeV for SM and anomalous couplings (a) $d=\pm 0.18$ and (b) $\tilde{d} = \pm 0.18$. The new definition of the azimuthal angle is used.