Into the multi-TeV scale with a Higgs golden ratio

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, Dγγ=σ(pp→H→γγ)/σ(pp→H→ZZ⁎→4ℓ±)Dγγ=σ(pp→H→γγ)/σ(pp→H→ZZ⁎→4ℓ±) 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−2g−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 HγγHγγ loop can be probed up to masses in the multi-TeV range and possibly larger than those accessible directly.