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.
Highlights
The newly begun LHC run will allow for a more thorough probing of the electroweak symmetry breaking (EWSB) scale and search for physics beyond the Standard Model (SM)
We examine various specific cases including the Minimal Supersymmetric Standard Model (MSSM) [10, 11], anomalous effective Higgs couplings to SM particles, and composite Higgs models
We show similar contours for the CP odd coupling which has been rescaled as cγ γ → (α /4π )( g N P v / M new physics (NP)
Summary
The newly begun LHC run will allow for a more thorough probing of the electroweak symmetry breaking (EWSB) scale and search for physics beyond the Standard Model (SM). By the two experiments [5,6] with the ≈ 25 fb−1 data collected at s = 7 + 8 TeV are shown, including the statistical (first) and the systematic (second) errors The latter involve systematic experimental errors, including ≈ 2.5% error due to the luminosity measurement, as well as the theoretical uncertainty due to scale variation (to account for missing higher orders) and the errors in the parametrization of the parton distribution functions (PDFs) and the measurement of the strong coupling constant (αs ). Particular when M H will be more precisely measured), D γ γ will be given by the ratio of the squared “reduced” Higgs coupling to photons and massive gauge bosons, D γ γ ∝ c γ2 /c 2V where c X ≡ g H X X / g SM Another interesting aspect of this ratio is that systematic uncertainties common to both channels, such as the one due to the luminosity, will cancel out leaving only the statistical errors. Because it involves the loop induced H → γ γ channel in which many charged particles could contribute, the decay ratio would allow us to probe more deeply the TeV scale as will be discussed with some examples below
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