Into the multi-TeV scale with a Higgs golden ratio

TL;DR

This paper proposes using the Higgs golden ratio, the ratio of its decay rates into two photons and four leptons, as a precise, ambiguity-free probe for new physics effects at the multi-TeV scale, especially with high-luminosity LHC data.

Contribution

It introduces the Higgs golden ratio as a theoretically clean observable that can be measured with high precision to detect new physics effects beyond current capabilities.

Findings

The ratio can be measured with percent-level accuracy at high-luminosity LHC.

It can constrain Higgs couplings to top quarks and vector bosons at the percent level.

It can probe new particles contributing to the Hγγ loop up to multi-TeV masses.

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, $D_{\gamma \gamma}= \sigma(pp\to H \to \gamma \gamma)/\sigma(pp\to H \to ZZ^* \to 4\ell^\pm)$ 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$\gamma\gamma$ loop can be probed up to masses in the multi-TeV range and possibly larger than those accessible directly.