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CMS-B2G-20-001 ; CERN-EP-2021-270
Search for resonances decaying to three W bosons in proton-proton collisions at $\sqrt{s} = $ 13 TeV
Phys. Rev. Lett. 129 (2022) 021802
Abstract: A search for resonances decaying into a W boson and a radion, where the radion decays into two W bosons, is presented. The data analyzed correspond to an integrated luminosity of 138 fb$^{-1}$ recorded in proton-proton collisions with the CMS detector at $\sqrt{s} = $ 13 TeV. One isolated charged lepton is required, together with one or two massive large-radius jets, containing the decay products of either two or one W bosons, respectively. No excess over the background estimation is observed. The results are combined with those from a complementary channel with an all-hadronic final state, described in an accompanying paper. Limits are set on parameters of an extended warped extra-dimensional model. These searches are the first of their kind at the LHC.
Figures Summary References CMS Publications
Figures

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Figure 1:
Schematic representation of the decay of a KK excitation ${\mathrm{W} _{\text {KK}}}$ to the final states considered in this analysis. Left: three individually reconstructed W bosons; right: one individually reconstructed W boson and two W bosons reconstructed as a single large-radius jet.

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Figure 2:
Background-only post-fit distribution of the reconstructed $\ell \nu $+jets system ${{m}_{\text {jj}\ell \nu}}$ in data and simulation for SR4. The shape of a triboson signal with $ {m_{{\mathrm{W} _{\text {KK}}}}} = $ 2.5 TeV and $ {m_{\mathrm{R}}} = $ 1 TeV is also shown as a violet solid line, normalized to the theoretical production cross section.

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Figure 3:
Pull distributions showing (Data-Prediction)/$\sigma _{\text {stat}}$ of the background-only fit to the reconstructed $\ell \nu $+jets system ${{m}_{\text {j}\ell \nu}}$ (${{m}_{\text {jj}\ell \nu}}$) for all SRs, where $\sigma _{\text {stat}}$ is the statistical uncertainty. Post-fit systematic uncertainties are indicated by the shaded bands. Examples of signal scenarios normalized to their theoretical production cross section are shown using solid, dashed, and dotted lines.

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Figure 4:
Observed upper limits at 95% CL on the product of the signal cross section and the branching fraction to three W bosons as functions of the ${\mathrm{W} _{\text {KK}}}$ and R resonance masses. Expected (dashed lines) and observed (solid lines) lower mass limits are shown as well for the particular parameters of the explored model. The blue straight dashed line indicates the border between merged and resolved radion cases. The limits obtained from this analysis are shown in red, and the results of the combination with Ref. [15] are shown in black.
Summary
In summary, a search has been presented for resonances decaying in cascade through $\mathrm{W_{KK}} \to \mathrm{WR}$ and $\mathrm{R \to WW}$ to three W bosons, where $\mathrm{W_{KK}}$ is a massive Kaluza--Klein excitation of a gauge boson and R is a scalar radion. The analysis is performed using proton-proton collision data at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb$^{-1}$. The final states considered contain one isolated charged lepton, missing transverse momentum, and one or two massive large-radius jets. Radion decay configurations with two W bosons merged in a single WW jet and those with two separated W boson jets are simultaneously probed by combining jet substructure algorithms. These novel radion identification and calibration technics are also applicable to Lorentz-boosted Higgs boson decays. Results agree with the predictions of the standard model and are combined with those of the analysis in the fully hadronic final state [15]. Limits are set on an extended warped extra-dimensional model. These are the first searches for the production of triboson resonances at the LHC.
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