CMS-B2G-17-005

CMS-B2G-17-005 ; CERN-EP-2018-023
Search for a heavy resonance decaying into a Z boson and a vector boson in the $\nu\overline{\nu}\mathrm{q}\mathrm{\bar{q}}$ final state
CMS Collaboration
10 March 2018
JHEP 07 (2018) 075
Abstract: A search is presented for a heavy resonance decaying into either a pair of Z bosons or a Z boson and a W boson (ZZ or WZ), with a Z boson decaying into a pair of neutrinos and the other boson decaying hadronically into two collimated quarks that are reconstructed as a highly energetic large-cone jet. The search is performed using the data collected with the CMS detector at the CERN LHC during 2016 in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to a total integrated luminosity of 35.9 fb$^{-1}$. No excess is observed in data with regard to background expectations. Results are interpreted in scenarios of physics beyond the standard model. Limits at 95% confidence level on production cross sections are set at 0.9 fb (63 fb) for spin-1 W' bosons, included in the heavy vector triplet model, with mass 4.0 TeV (1.0 TeV), and at 0.5 fb (40 fb) for spin-2 bulk gravitons with mass 4.0 TeV (1.0 TeV). Lower limits are set on the masses of W' bosons in the context of two versions of the heavy vector triplet model of 3.1 TeV and 3.4 TeV, respectively.
Links: e-print arXiv:1803.03838 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ;

Figures	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Comparison of data and simulated events. Left: the corrected mass of the leading AK8 jet, interpreted as the hadronically decaying vector boson. Right: the distribution of the ${\tau _{21}}$ subjettiness of the vector boson candidate, which is used to define low- and high-purity categories. The background processes predicted by the SM are depicted as colored filled histograms. The shaded area on top of the histograms represents the statistical uncertainty associated to MC simulations. Overflows are shown in the rightmost bin. Two possible signal hypotheses are shown: a spin-1 W' boson with a mass of 3 TeV and a spin-2 bulk graviton with a mass of 1 TeV. The data points are shown by the black markers, along with their associated statistical uncertainties. In the bottom panels, the ratio between data and MC predictions is calculated for each bin.
png pdf	Figure 1-a: Comparison of data and simulated events: the corrected mass of the leading AK8 jet, interpreted as the hadronically decaying vector boson. The background processes predicted by the SM are depicted as colored filled histograms. The shaded area on top of the histograms represents the statistical uncertainty associated to MC simulations. Overflows are shown in the rightmost bin. Two possible signal hypotheses are shown: a spin-1 W' boson with a mass of 3 TeV and a spin-2 bulk graviton with a mass of 1 TeV. The data points are shown by the black markers, along with their associated statistical uncertainties. In the bottom panel, the ratio between data and MC predictions is calculated for each bin.
png pdf	Figure 1-b: Comparison of data and simulated events: the distribution of the ${\tau _{21}}$ subjettiness of the vector boson candidate, which is used to define low- and high-purity categories. The background processes predicted by the SM are depicted as colored filled histograms. The shaded area on top of the histograms represents the statistical uncertainty associated to MC simulations. Overflows are shown in the rightmost bin. Two possible signal hypotheses are shown: a spin-1 W' boson with a mass of 3 TeV and a spin-2 bulk graviton with a mass of 1 TeV. The data points are shown by the black markers, along with their associated statistical uncertainties. In the bottom panel, the ratio between data and MC predictions is calculated for each bin.
png pdf	Figure 2: Background yield prediction in the signal region obtained with the $\alpha $ method, in the low-purity (left) and high-purity (right) categories. Background processes predicted by the SM are depicted as colored areas bounded by smooth functions. The bottom panels show fit residuals normalized to their uncertainties.
png pdf	Figure 2-a: Background yield prediction in the signal region obtained with the $\alpha $ method, in the low-purity category. Background processes predicted by the SM are depicted as colored areas bounded by smooth functions. The bottom panel shows fit residuals normalized to their uncertainties.
png pdf	Figure 2-b: Background yield prediction in the signal region obtained with the $\alpha $ method, in the high-purity category. Background processes predicted by the SM are depicted as colored areas bounded by smooth functions. The bottom panel shows fit residuals normalized to their uncertainties.
png pdf	Figure 3: Expected background shapes as a function of the transverse mass of the diboson candidate obtained using the $\alpha $ method in the low-purity (left) and high-purity (right) categories, represented as colored areas bounded by smooth functions. As a reference, the expected distribution of a W' with a mass of 3 TeV decaying into a W boson and a Z boson is displayed. Data are shown as black markers.
png pdf	Figure 3-a: Expected background shapes as a function of the transverse mass of the diboson candidate obtained using the $\alpha $ method in the low-purity category, represented as colored areas bounded by smooth functions. As a reference, the expected distribution of a W' with a mass of 3 TeV decaying into a W boson and a Z boson is displayed. Data are shown as black markers.
png pdf	Figure 3-b: Expected background shapes as a function of the transverse mass of the diboson candidate obtained using the $\alpha $ method in the high-purity category, represented as colored areas bounded by smooth functions. As a reference, the expected distribution of a W' with a mass of 3 TeV decaying into a W boson and a Z boson is displayed. Data are shown as black markers.
png pdf	Figure 4: The observed and expected limits on the product of the cross section and branching fraction $\sigma \mathcal {B} ({\mathrm {W}'} \to {\mathrm {W}}_{\text {had}} {\mathrm {Z}} _{\text {inv}})$ for a spin-1 HVT signal hypothesis (left) and $\sigma \mathcal {B} ({\mathrm {G}}\to {\mathrm {Z}} _{\text {had}} {\mathrm {Z}} _{\text {inv}})$ for a spin-2 bulk graviton signal hypothesis (right), as a function of the mass of the diboson resonance. The low- and high-purity categories have been combined. The inner and outer shaded bands indicate the 68% and 95% uncertainty intervals associated with the expected limits. Theoretical predictions are shown for: (left) the two HVT models considered, model A (blue dotted-and-dashed line) and model B (red solid line), and (right) a graviton model with a curvature parameter of $ {\tilde{k}} =$ 0.5 (violet solid line).
png pdf	Figure 4-a: The observed and expected limits on the product of the cross section and branching fraction $\sigma \mathcal {B} ({\mathrm {W}'} \to {\mathrm {W}}_{\text {had}} {\mathrm {Z}} _{\text {inv}})$ for a spin-1 HVT signal hypothesis, as a function of the mass of the diboson resonance. The low- and high-purity categories have been combined. The inner and outer shaded bands indicate the 68% and 95% uncertainty intervals associated with the expected limits. Theoretical predictions are shown for: (left) the two HVT models considered, model A (blue dotted-and-dashed line) and model B (red solid line), and (right) a graviton model with a curvature parameter of $ {\tilde{k}} =$ 0.5 (violet solid line).
png pdf	Figure 4-b: The observed and expected limits on the product of the cross section and branching fraction $\sigma \mathcal {B} ({\mathrm {G}}\to {\mathrm {Z}} _{\text {had}} {\mathrm {Z}} _{\text {inv}})$ for a spin-2 bulk graviton signal hypothesis, as a function of the mass of the diboson resonance. The low- and high-purity categories have been combined. The inner and outer shaded bands indicate the 68% and 95% uncertainty intervals associated with the expected limits. Theoretical predictions are shown for: (left) the two HVT models considered, model A (blue dotted-and-dashed line) and model B (red solid line), and (right) a graviton model with a curvature parameter of $ {\tilde{k}} =$ 0.5 (violet solid line).

Summary

A search has been made for heavy diboson resonances (WZ, ZZ) decaying into a pair of vector bosons, one of which is a Z boson decaying into $\nu\overline{\nu}$ and the other is a W or Z boson that decays into $\mathrm{q}\mathrm{\bar{q}}$. The data were collected by the CMS detector from proton-proton collisions produced at the LHC at a center-of-mass energy of 13 TeV. In this analysis, the hadronically decaying W or Z boson is reconstructed as a large-cone jet. The invisible decay of the Z boson manifests itself as a large amount of missing transverse momentum recoiling against the jet. The transverse components of the VZ system momentum are used to define the transverse mass variable, where a search for a localized excess is performed. The expected background is described with a hybrid data/simulation approach that takes advantage of data sidebands to predict the background normalization and shape in the signal region. To improve the discovery potential, two purity categories are defined, based on jet substructure observables. An unbinned maximum likelihood fit is performed. No excess is observed in data compared to standard model predictions. Upper limits are established at 95% confidence level on the product of the production cross section and branching fraction for a spin-1 heavy vector triplet (HVT) W' boson and spin-2 bulk graviton, which are in the range 0.9-63 fb and 0.5-40 fb, respectively, depending on the resonance mass. The existence of a W' boson is excluded at 95% confidence level up to a mass of 3.1 TeV in HVT model A and up to 3.4 TeV in HVT model B.

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