Abstract
In this paper, we constrain CP violation in the Higgs sector using the measured signal strengths in the various Higgs search channels. To this end, we introduce a general parameterization for a resonance which is an admixture of a CP-even Higgs-like state and a CP-odd scalar. By performing a fit to the available data from the Tevatron and LHC experiments one obtains constraints on the mixing angle and the couplings of the resonance to Standard Model fields. Depending on the couplings, sizable mixing angles are still compatible with the data, but small mixing is in general preferred by the fit. In particular we find that a pure CP-odd state is disfavored by the current data at the 3 sigma level. Additionally we consider a mixed fermiophobic resonance and a model with two degenerate mixed resonances and find that both scenarios can successfully fit the data within current errors. Finally, we estimate that the mixing angle can be constrained to \alpha < 1.1 (0.7) in the full 8 TeV (14 TeV) run of the LHC.
Highlights
The ATLAS and CMS collaborations have reported on the discovery of a new bosonic resonance with mass in the range 125–126 GeV at the Large Hadron Collider (LHC) [1, 2], which has been corroborated by an excess observed by the CDF and DØ experiments at the Tevatron [3, 4]
Since both these searches and the inclusive LHC measurements receive contributions from gluon fusion and VBF, there is some degree of correlation between them, which is taken into account with a covariance matrix in the χ2 fit
The 125-GeV resonance φ has been assumed to be a general mixture between a CPeven and CP-odd scalar field, and bounds on the mixing angle have been derived in a variety of different scenarios: (i) fermion Yukawa couplings fixed to their Standard Model values; (ii) the overall scale of up-type and down-type Yukawa couplings to the CP-even and CP-odd components may float freely and independently; (iii) the signal peak near 125 GeV is comprised of two particles, φ and φ′, which are the two mass eigenstates of the mixed CP-even and CP-odd scalar fields; (iv) addition of higher-dimensional operators that couple the CP-odd component to gauge bosons; (v) a special case of (iv) with vanishing Yukawa couplings
Summary
The ATLAS and CMS collaborations have reported on the discovery of a new bosonic resonance with mass in the range 125–126 GeV at the Large Hadron Collider (LHC) [1, 2], which has been corroborated by an excess observed by the CDF and DØ experiments at the Tevatron [3, 4]. The analysis of distributions becomes viable only if a sufficient number of events has been accumulated in a given channel At this early stage, one can already constrain the CP properties from the observed production rates and decay branching fractions [14,15]. One can already constrain the CP properties from the observed production rates and decay branching fractions [14,15] This mainly follows from the fact that a CP-odd even-spin particle cannot have renormalizable tree-level couplings to two gauge bosons. The goal of this paper is to carry out such a fit in a general setup where the 125-GeV resonance can be an arbitrary mixture of CP-even and CP-odd components, and can have modified couplings to SM fermions as well as new couplings to SM gauge bosons mediated through higher-dimensional operators. We do not consider dimension-five operators for the coupling of the CP-even component H to gauge bosons since the effects are typically small compared to the treelevel HW W and HZZ couplings, while the loop-induced Hγγ and Hgg interactions can be sufficiently generally described by the modified Yukawa couplings in eq (3)
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