Into the multi-TeV scale with a Higgs golden ratio

Abstract With the upgrade of the LHC, the couplings of the observed Higgs particle to fermions and gauge bosons will be measured with a much higher experimental accuracy than current measurements, but will still be limited by an order 10% theoretical uncertainty. In this paper, we re-emphasize the fact that the ratio of Higgs signal rates into two photons and four leptons, D γ γ = σ ( p p → H → γ γ ) / σ ( p p → H → Z Z ⁎ → 4 ℓ ± ) can be made free of these ambiguities. Its measurement would be limited only by the statistical and systematic errors, which can in principle be reduced to the percent level at a high-luminosity LHC. This decay ratio would then provide a powerful probe of new physics effects in addition to high precision electroweak observables or the muon g − 2 . As an example, we show that the Higgs couplings to top quarks and vector bosons can be constrained at the percent level and that new Higgs or supersymmetric particles that contribute to the H γ γ loop can be probed up to masses in the multi-TeV range and possibly larger than those accessible directly.