Abstract
A recent study [1] has shown that a simplified model predicting a heavy scalar of mass 270 GeV (H ) that decays to a Standard Model (SM) Higgs boson in association with a scalar singlet of mass 150 GeV (S) can accommodate several anomalous multi-lepton results in proton-proton collisions at the Large Hadron Collider (LHC). With this in mind, the goal of this article is to provide a more formal study of a wider set of LHC results pertaining to the production of multiple leptons. We find that a combination of such results lead to strong discrepancies between the data and SM Monte Carlo predictions. These discrepancies appear in corners of the phase-space where different SM processes dominate, indicating that the potential mismodeling of a single SM process is unlikely to explain them. Systematic uncertainties from the prediction of SM processes evaluated with currently available tools seem unable to explain away these discrepancies. A combination is able to constrain the simplified model’s single degree of freedom β2, related to the size of the Yukawa coupling of H to the top quark, to a value of 2.92 ± 0.35. This is in contrast to the absence of signal, where βg = 0. This result is discussed in the independent contexts of both potential for new physics in the existing LHC data as well as the limitations of our current understanding of the SM. That being said, QCD NNLO and EW NLO corrections in di-lepton final states are not expected to change the conclusions of this study. New results pertaining to the production of two opposite sign different flavour charged leptons with a full jet veto further confirm the presence of anomalies in similar corners of the leptonic phase-space.
Highlights
Set of ATLAS and CMS physics results could be fit with a significance of 3σ
Seeing as though this was made on an early set of Large Hadron Collider (LHC) results, it is quite likely that the statistical significance of the fit was influenced by fluctuations in the data — see for instance the magnitude of the distortions in the ATLAS Higgs boson pT spectra [8, 9]; more recent independent measurements have shown much milder distortions around lower values of pT [23,24,25]
The variable that is used to fit the BSM prediction is the highest pseudo-rapidity (η) for high pT jets. This decision was made based on the fact that the systematic uncertainty on the Standard Model (SM) is smaller for this variable than that of the other variables considered in the search
Summary
H is assumed to be linked to electro-weak symmetry breaking in that it has Yukawa couplings and tree-level couplings with the weak vector bosons V (W ± and Z). The couplings in equation (2.3) are chosen to be globally re-scaled Higgs-like couplings This is somewhat an arbitrary choice, it has the dual advantage of fixing the BRs of S (which in turn reduces the number of free parameters in the model) and suppressing the direct production of S. The latter advantage is motivated by the LHC data, since there have been no observations of directly produced Higgs-like bosons near a mass of 150 GeV at the LHC as of yet.
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