CMS-B2G-16-007

CMS-B2G-16-007 ; CERN-EP-2017-077
Combination of searches for heavy resonances decaying to WW, WZ, ZZ, WH, and ZH boson pairs in proton-proton collisions at $\sqrt{s} = $ 8 and 13 TeV
CMS Collaboration
25 May 2017
Phys. Lett. B 774 (2017) 533
Abstract: A statistical combination of searches is presented for massive resonances decaying to WW, WZ, ZZ, WH, and ZH boson pairs in proton-proton collision data collected by the CMS experiment at the LHC. The data are taken at centre-of-mass energies of 8 and 13 TeV, corresponding to respective integrated luminosities of 19.7 and up to 2.7 fb$^{-1}$. The results are interpreted in the context of heavy vector triplet and singlet models that mimic properties of composite-Higgs models predicting W' and Z' bosons decaying to WZ, WW, WH, and ZH bosons. A model with a bulk graviton that decays into WW and ZZ is also considered. This is the first combined search for WW, WZ, WH, and ZH resonances and yields lower limits on masses at 95% confidence level for W' and Z' singlets at 2.3 TeV, and for a triplet at 2.4 TeV. The limits on the production cross section of a narrow bulk graviton resonance with the curvature scale of the warped extra dimension $\tilde{k}= $ 0.5, in the mass range of 0.6 to 4.0 TeV, are the most stringent published to date.
Links: e-print arXiv:1705.09171 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Exclusion limits at 95% CL for HVT models A (left) and B (right) on the signal strengths for the singlets $\mathrm{W}' \to \mathrm{ W } \mathrm{ Z } $ and $\mathrm{ W } \mathrm{ H } $ (upper), and $\mathrm{Z}' \to \mathrm{ W } \mathrm{ W } $ and $\mathrm{ Z } \mathrm{ H } $ (lower) as a function of the resonance mass, obtained by combining the 8 and 13 TeV analyses. The signal strength is defined as the ratio of the excluded cross section and the theoretical prediction. The curves with symbols refer to the different inputs to the combinations. The thick solid (dashed) line represents the combined observed (expected) limits.
png pdf	Figure 1-a: Exclusion limits at 95% CL for HVT model A on the signal strengths for the singlet $\mathrm{W}' \to \mathrm{ W } \mathrm{ Z } $ and $\mathrm{ W } \mathrm{ H } $ as a function of the resonance mass, obtained by combining the 8 and 13 TeV analyses. The signal strength is defined as the ratio of the excluded cross section and the theoretical prediction. The curves with symbols refer to the different inputs to the combinations. The thick solid (dashed) line represents the combined observed (expected) limits.
png pdf	Figure 1-b: Exclusion limits at 95% CL for HVT model B on the signal strengths for the singlet $\mathrm{W}' \to \mathrm{ W } \mathrm{ Z } $ and $\mathrm{ W } \mathrm{ H } $ as a function of the resonance mass, obtained by combining the 8 and 13 TeV analyses. The signal strength is defined as the ratio of the excluded cross section and the theoretical prediction. The curves with symbols refer to the different inputs to the combinations. The thick solid (dashed) line represents the combined observed (expected) limits.
png pdf	Figure 1-c: Exclusion limits at 95% CL for HVT model A on the signal strengths for the singlet $\mathrm{Z}' \to \mathrm{ W } \mathrm{ W } $ and $\mathrm{ Z } \mathrm{ H } $ as a function of the resonance mass, obtained by combining the 8 and 13 TeV analyses. The signal strength is defined as the ratio of the excluded cross section and the theoretical prediction. The curves with symbols refer to the different inputs to the combinations. The thick solid (dashed) line represents the combined observed (expected) limits.
png pdf	Figure 1-d: Exclusion limits at 95% CL for HVT model B on the signal strengths for the singlet $\mathrm{Z}' \to \mathrm{ W } \mathrm{ W } $ and $\mathrm{ Z } \mathrm{ H } $ as a function of the resonance mass, obtained by combining the 8 and 13 TeV analyses. The signal strength is defined as the ratio of the excluded cross section and the theoretical prediction. The curves with symbols refer to the different inputs to the combinations. The thick solid (dashed) line represents the combined observed (expected) limits.
png pdf	Figure 2: Exclusion limits at 95% CL on the signal strengths in HVT models A (upper left) and B (upper right) for the triplet V', as a function of the resonance mass, obtained by combining the 8 and 13 TeV diboson searches. The signal strength is defined as the ratio of the excluded cross section and the theoretical prediction. In the upper plots, the curves with symbols refer to the different inputs to the combination. The thick solid (dashed) line represents the combined observed (expected) limits. In the lower plot, exclusion regions in the plane of the HVT-model couplings ($g_\mathrm {V}c_{\mathrm{ H } }$, $g^2c_\mathrm {F}/g_\mathrm {V}$ ) for three resonance masses of 1.5, 2.0, and 3.0 TeV, where $g$ denotes the weak gauge coupling. The points A and B of the benchmark models used in the analysis are also shown. The boundaries of the regions excluded in this search are indicated by the solid, dashed, and dashed-dotted lines. The areas indicated by the solid shading correspond to regions where the resonance width is predicted to be more than 5% of the resonance mass, in which the narrow-resonance assumption is not satisfied.
png pdf	Figure 2-a: Exclusion limits at 95% CL on the signal strengths in HVT model A for the triplet V', as a function of the resonance mass, obtained by combining the 8 and 13 TeV diboson searches. The signal strength is defined as the ratio of the excluded cross section and the theoretical prediction. In the upper plots, the curves with symbols refer to the different inputs to the combination. The thick solid (dashed) line represents the combined observed (expected) limits.
png pdf	Figure 2-b: Exclusion limits at 95% CL on the signal strengths in HVT model B for the triplet V', as a function of the resonance mass, obtained by combining the 8 and 13 TeV diboson searches. The signal strength is defined as the ratio of the excluded cross section and the theoretical prediction. In the upper plots, the curves with symbols refer to the different inputs to the combination. The thick solid (dashed) line represents the combined observed (expected) limits.
png pdf	Figure 2-c: In this plot, exclusion regions in the plane of the HVT-model couplings ($g_\mathrm {V}c_{\mathrm{ H } }$, $g^2c_\mathrm {F}/g_\mathrm {V}$ ) for three resonance masses of 1.5, 2.0, and 3.0 TeV, where $g$ denotes the weak gauge coupling. The points A and B of the benchmark models used in the analysis are also shown. The boundaries of the regions excluded in this search are indicated by the solid, dashed, and dashed-dotted lines. The areas indicated by the solid shading correspond to regions where the resonance width is predicted to be more than 5% of the resonance mass, in which the narrow-resonance assumption is not satisfied.
png pdf	Figure 3: Exclusion limits at 95% CL on the signal strength in the bulk graviton model with $\tilde{k} = $ 0.5, as a function of the resonance mass, obtained by combining the 8 and 13 TeV diboson searches. The signal strength is defined as the ratio of the excluded cross section and the theoretical prediction. The curves with symbols refer to the different inputs to the combination. The thick solid (dashed) line represents the combined observed (expected) limits.

Tables
png pdf	Table 1: Summary of the properties of the heavy-resonance models considered in the combination. The polarization of the produced W and Z bosons in these models is primarily longitudinal, as decays to transverse polarizations are suppressed.
png pdf	Table 2: Summary of signal efficiencies in analysis channels for 2 TeV resonances in the different models under study. For analyses that define high-purity (HP) and low-purity (LP) categories, both efficiencies are quoted in the form HP/LP. Signal efficiencies are given in percent, and include the SM branching fractions of the bosons to the final state in the analysis channel, effects from detector acceptance, as well as reconstruction and selection efficiencies. Dashes indicate negligible signal contributions that are not considered in the overall combination. Channels marked with an asterisk have been reinterpreted for this combination, as described in the text later.
png pdf	Table 3: Correlation across analyses of systematic uncertainties in the signal prediction affecting the event yield in the signal region and the reconstructed diboson invariant mass distribution. A ``yes'' signifies 100% correlation, and ``no'' means uncorrelated.
png pdf	Table 4: Lower limits at 95% CL on the resonance masses in HVT models A and B.
png pdf	Table 5: Signal cross sections in units of fb at 8 TeV center-of-mass energy. HVT model A and model B cross sections are quoted in the form $\sigma _{\text {Model A}}/\sigma _{\text {Model B}}$.
png pdf	Table 6: Signal cross sections in units of fb at 13 TeV center-of-mass energy. HVT model A and model B cross sections are quoted in the form $\sigma _{\text {Model A}}/\sigma _{\text {Model B}}$.

Summary

A statistical combination of searches for massive narrow resonances decaying to WW, ZZ, WZ, WH, and ZH boson pairs in the mass range 0.6-4.0 TeV has been presented. The searches are based on proton-proton collision data collected by the CMS experiment at centre-of-mass energies of 8 and 13 TeV, corresponding to integrated luminosities of 19.7 and up to 2.7 fb$^{-1}$, respectively. The results of the searches and of the combination are interpreted in the context of heavy vector singlet and triplet models predicting W' and Z' bosons decaying to WZ, WH, WW, and ZH, and a model with a bulk graviton that decays into WW and ZZ. The small excesses observed with 8 TeV data by the ATLAS and CMS experiments [21,16] at 1.8-2.0 TeV are not confirmed by the analyses performed with 13 TeV data. This is the first combined search for WW, WZ, WH, and ZH resonances and yields 95% confidence level lower limits in the heavy vector triplet model B on the masses of W' and Z' singlets at 2.3 TeV, and on a heavy vector triplet at 2.4 TeV. The limits on the production cross section of a narrow bulk graviton resonance with the curvature scale of the warped extra dimension $\tilde{k}= $ 0.5, in the mass range of 0.6 to 4.0 TeV, are the most stringent published to date. The statistical combination of VV and VH resonance searches in 12 distinct final states was found to yield a significant gain in sensitivity and therefore represents a powerful tool for future resonance searches with the large expected diboson event data sample at the LHC.

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