Search for heavy resonances that decay into a vector boson and a Higgs boson in hadronic final states at s = 13 TeV

Abstract

A search for heavy resonances with masses above 1 $\text{TeV}$ , decaying to final states containing a vector boson and a Higgs boson, is presented. The search considers hadronic decays of the vector boson, and Higgs boson decays to b quarks. The decay products are highly boosted, and each collimated pair of quarks is reconstructed as a single, massive jet. The analysis is performed using a data sample collected in 2016 by the CMS experiment at the LHC in proton-proton collisions at a center-of-mass energy of 13 $\text{TeV}$ , corresponding to an integrated luminosity of 35.9 ${\text{fb}}^{-1}$ . The data are consistent with the background expectation and are used to place limits on the parameters of a theoretical model with a heavy vector triplet. In the benchmark scenario with mass-degenerate $W^{{}^{\text{'}}}$ and $Z^{\text{'}}$ bosons decaying predominantly to pairs of standard model bosons, for the first time heavy resonances for masses as high as 3.3 $\text{TeV}$ are excluded at 95% confidence level, setting the most stringent constraints to date on such states decaying into a vector boson and a Higgs boson.

Keywords: B2G; CMS; Diboson; Hadronic; Higgs; Physics; VH.

Fig. 1

Distribution of the soft-drop PUPPI mass after the kinematic selections on the two jets, for data, simulated background, and signal. The signal events with low mass correspond to boson decays where one of the two quarks is emitted outside the jet cone or the two quarks are overlapping. The distributions are normalized to the number of events observed in data. The dashed vertical lines represent the boundaries between the jet mass categories

Fig. 2

Distribution of the N-subjettiness ${\mathit{\tau }}_{21}$ (upper) and b tagging discriminator output (lower) after the kinematic selections on the two jets, for data, simulated background, and signal. The distributions are normalized to the number of events observed in data. The dashed vertical lines represent the boundaries between the categories as described in the text

Fig. 3

Dijet invariant distribution $m_{\mathrm{V}\mathrm{H}}$ of the two leading jets in the $\mathrm{W}$ mass region: high purity (upper) and low purity (lower) categories, with tight (left) and loose (right) b tagging selections. The preferred background-only fit is shown as a solid blue line with an associated shaded band indicating the uncertainty. An alternative fit is shown as a purple dashed line. The ratio panels show the pulls in each bin, $(N^{\text{data}}-N^{\text{bkg}})/\mathit{\sigma }$, where $\mathit{\sigma }$ is the Poisson uncertainty in data. The horizontal bars on the data points indicate the bin width and the vertical bars represent the normalized Poisson errors, and are shown also for bins with zero entries up to the highest $m_{\mathrm{V}\mathrm{H}}$ event. The expected contribution of a resonance with $m_{\mathrm{X}}=2000\text{GeV}$, simulated in the context of the HVT model B, is shown as a dot-dashed red line

Fig. 4

Dijet invariant distribution $m_{\mathrm{V}\mathrm{H}}$ of the two leading jets in the $\mathrm{Z}$ mass region: high purity (upper) and low purity (lower) categories, with tight (left) and loose (right) b tagging selections. The preferred background-only fit is shown as a solid blue line with an associated shaded band indicating the uncertainty. An alternative fit is shown as a purple dashed line. The ratio panels show the pulls in each bin, $(N^{\text{data}}-N^{\text{bkg}})/\mathit{\sigma }$, where $\mathit{\sigma }$ is the Poisson uncertainty in data. The horizontal bars on the data points indicate the bin width and the vertical bars represent the normalized Poisson errors, and are shown also for bins with zero entries up to the highest $m_{\mathrm{V}\mathrm{H}}$ event. The expected contribution of a resonance with $m_{\mathrm{X}}=2000\text{GeV}$, simulated in the context of the HVT model B, is shown as a dot-dashed red line

Fig. 5

Observed and expected 95% CL upper limits on the product $\mathit{\sigma }(\mathrm{X})\mathcal{B}(\mathrm{X}\to \mathrm{W}\mathrm{H})\mathcal{B}(\mathrm{H}\to \mathrm{b}\overline{\mathrm{b}})$ (upper) and $\mathit{\sigma }(\mathrm{X})\mathcal{B}(\mathrm{X}\to \mathrm{Z}\mathrm{H})\mathcal{B}(\mathrm{H}\to \mathrm{b}\overline{\mathrm{b}})$ (lower) as a function of the resonance mass for a single narrow spin-1 resonance, for the combination of the eight categories, and including all statistical and systematic uncertainties. The inner green and outer yellow bands represent the $\pm 1$ and $\pm 2$ standard deviation uncertainties in the expected limit. The purple and red solid curves correspond to the cross sections predicted by the HVT model A and model B, respectively

Fig. 6

Observed and expected 95% CL upper limits with the $\pm 1$ and $\pm 2$ standard deviation uncertainty bands on the product $\mathit{\sigma }(\mathrm{X})\mathcal{B}(\mathrm{X}\to \mathrm{V}\mathrm{H})\mathcal{B}(\mathrm{H}\to \mathrm{b}\overline{\mathrm{b}})$ in the combined heavy vector triplet hypothesis, for the combination of the eight categories. The purple and red solid curves correspond to the cross sections predicted by the HVT model A and model B, respectively

Fig. 7

Observed exclusion in the HVT parameter plane $\left[g_{\text{V}}{c}_{\text{H}},g^2{c}_{\text{F}}/g_{\text{V}}\right]$ for three different resonance masses (1.5, 2.0, and 3.0 $\text{TeV}$). The parameter $g_{\text{V}}$ represents the coupling strength of the new interaction, $c_{\text{H}}$ the coupling between the HVT bosons and the Higgs boson and longitudinally polarized SM vector bosons, and $c_{\text{F}}$ the coupling between the heavy vector bosons and the SM fermions. The benchmark scenarios corresponding to HVT model A and model B are represented by a purple cross and a red point. The gray shaded areas correspond to the region where the resonance natural width is predicted to be larger than the typical experimental resolution (4%) and thus the narrow-width approximation does not apply