Constraints on the spin-parity and anomalous HVV couplings of the Higgs boson in proton collisions at 7 and 8 TeV

TL;DR

This CMS analysis confronts the spin-parity and tensor structure of the Higgs-like boson using Run 1 data across H→ZZ→4ℓ, Zγ*, γ*γ*→4ℓ, H→WW→ℓνℓν, and H→γγ channels. It employs matrix-element likelihood (MELA) and template methods to constrain eleven anomalous HVV couplings under spin-0, as well as mixed-spin 1 and 2 hypotheses, testing production dependencies and interference effects. The exotic-spin searches exclude all non-SM spin scenarios with high confidence, while the spin-zero study yields tight constraints on HVV couplings and CP properties, including the first constraints on HZγ and Hγγ in the 4ℓ channel. The combined ZZ and WW analyses strengthen limits, and the overall results are consistent with the SM Higgs boson quantum numbers JPC=0++ at 125.6 GeV, with no evidence for CP violation in these interactions at current sensitivity.

Abstract

The study of the spin-parity and tensor structure of the interactions of the recently discovered Higgs boson is performed using the H to ZZ, Z gamma*, gamma* gamma* to 4 l, H to WW to l nu l nu, and H to gamma gamma decay modes. The full dataset recorded by the CMS experiment during the LHC Run 1 is used, corresponding to an integrated luminosity of up to 5.1 inverse femtobarns at a center-of-mass energy of 7 TeV and up to 19.7 inverse femtobarns at 8 TeV. A wide range of spin-two models is excluded at a 99% confidence level or higher, or at a 99.87% confidence level for the minimal gravity-like couplings, regardless of whether assumptions are made on the production mechanism. Any mixed-parity spin-one state is excluded in the ZZ and WW modes at a greater than 99.999% confidence level. Under the hypothesis that the resonance is a spin-zero boson, the tensor structure of the interactions of the Higgs boson with two vector bosons ZZ, Z gamma, gamma gamma, and WW is investigated and limits on eleven anomalous contributions are set. Tighter constraints on anomalous HVV interactions are obtained by combining the HZZ and HWW measurements. All observations are consistent with the expectations for the standard model Higgs boson with the quantum numbers J[PC]=0[++].

Figures (26)

• Figure 1: Illustration of the production of a system ${X}\xspace$ in a parton collision and its decay to two vector bosons ${g}\xspace{g}\xspace$ or $\mathrm{q}\mathrm{\overline{q}}\xspace \to {X}\xspace\to {Z}\xspace{Z}\xspace, \mathrm{W}\mathrm{W}, {Z}\xspace\gamma,$ and $\gamma\gamma$ either with or without sequential decay of each vector boson to a fermion-antifermion pair Gao:2010qxCabibbo:1965zz. The two production angles $\theta^*$ and $\Phi_1$ are shown in the ${X}\xspace$ rest frame and the three decay angles $\theta_1$, $\theta_2$, and $\Phi$ are shown in the ${V}\xspace$ rest frames. Here ${X}\xspace$ stands either for a Higgs boson, an exotic particle, or, in general, the genuine or misidentified ${V}\xspace{V}\xspace$ system, including background.
• Figure 2: Distributions of the eight kinematic observables used in the ${H}\xspace\to{V}\xspace{V}\xspace\to4\ell$ analysis: $m_{4\ell}$, $m_1$, $m_2$, $\cos\theta^*$, $\cos\theta_{1}$, $\cos\theta_{2}$, $\Phi$, and $\Phi_{1}$. The observed data (points with error bars), the expectations for the SM background (shaded areas), the SM Higgs boson signal (open areas under the solid histogram), and the alternative spin-zero resonances (open areas under the dashed histograms) are shown, as indicated in the legend. The mass of the resonance is taken to be 125.6$\,\text{Ge\spaceV}$ and the SM cross section is used. All distributions, with the exception of $m_{4\ell}$, are presented with the requirement $121.5 < m_{4\ell} < 130.5$$\,\text{Ge\spaceV}$.
• Figure 3: Distributions of $m_{\ell\ell}\xspace$ (left) and $m_\mathrm{T}\xspace$ (right) for events with 0 jets (upper row) and 1 jet (lower row) in the ${H}\xspace\to\mathrm{W}\mathrm{W}\to\ell\nu\ell\nu$ analysis. The observed data (points with error bars), the expectations for the SM background (shaded areas), the SM Higgs boson signal (open areas under the solid histogram), and the alternative spin-zero resonance (open areas under the dashed histograms) are shown, as indicated in the legend. The mass of the resonance is taken to be 125.6$\,\text{Ge\spaceV}$ and the SM cross section is used.
• Figure 4: Distributions of the kinematic discriminants for the observed data (points with error bars), the expectations for the SM background (shaded areas), the SM Higgs boson signal (open areas under the solid histogram), and the alternative spin-zero resonances (open areas under the dashed histograms) are shown, as indicated in the legend. The mass of the resonance is taken to be 125.6$\,\text{Ge\spaceV}$ and the SM cross section is used. Top row from left to right: $\mathcal{D}_\text{bkg}$, $\mathcal{D}_{0-}$, $\mathcal{D}_{C\!P}$; bottom row from left to right: $\mathcal{D}_{0h+}$, $\mathcal{D}_\text{int}$, $\mathcal{D}_{\Lambda1}$. All distributions, with the exception of $\mathcal{D}_\text{bkg}$, are shown with the requirement $\mathcal{D}_\text{bkg}>0.5$ to enhance signal purity.
• Figure 5: (top) Distributions of the test statistic $q=-2\ln(\mathcal{L}_{J^P}/\mathcal{L}_{0^+})$ for the $J^P=1^+$ hypothesis of $\mathrm{q}\mathrm{\overline{q}}\xspace\to{X}\xspace(1^+)\to {Z}\xspace{Z}\xspace$ tested against the SM Higgs boson hypothesis ($0^+$). The expectation for the SM Higgs boson is represented by the yellow histogram on the right and the alternative $J^P$ hypothesis by the blue histogram on the left. The red arrow indicates the observed $q$ value. (bottom) Observed value of $-2\Delta\ln\mathcal{L}$ as a function of $f(J^P)$ and the expectation in the SM for the $\mathrm{q}\mathrm{\overline{q}}\xspace\to{X}\xspace(1^+)\to {Z}\xspace{Z}\xspace$ alternative $J^P$ model.