CMS-EXO-17-008 ; CERN-EP-2018-202 | ||
Search for a W' boson decaying to a $\tau$ lepton and a neutrino in proton-proton collisions at $\sqrt{s} = $ 13 TeV | ||
CMS Collaboration | ||
31 July 2018 | ||
Phys. Lett. B 792 (2019) 107 | ||
Abstract: A search for a new high-mass resonance decaying to a tau lepton and a neutrino is reported. The analysis uses proton-proton collision data collected by the CMS experiment at the LHC at $\sqrt{s} = $ 13 TeV, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. The search utilizes hadronically decaying tau leptons. No excess in the event yield is observed at high transverse masses of the $\tau$ and missing transverse momentum. An interpretation of results within the sequential standard model excludes W' boson masses below 4.0 TeV at 95% confidence level. Existing limits are also improved on models in which the W' boson decays preferentially to fermions of the third generation. Heavy W' bosons with masses less than 1.7-3.9 TeV, depending on the coupling in the non-universal G(221) model, are excluded at 95% confidence level. These are the most stringent limits on this model to date. | ||
Links: e-print arXiv:1807.11421 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ; |
Figures | |
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Figure 1:
Leading order Feynman diagram of the expected signal process $ {\mathrm {W}'} \to {\tau} {\nu}$. |
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Figure 2:
Branching fractions $\mathcal {B}({\mathrm {W}'})$ as a function of the mixing angle $\cot\theta _{\mathrm {E}}$, for W' boson decays in the NUGIM G(221) framework, as calculated in Refs. [2,21,22]. For $\cot\theta _{\mathrm {E}} = $ 1 the values correspond to those in the SSM, rescaled to accommodate the WH decay channel. |
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Figure 3:
(Left) The $ {m_{\mathrm {T}}} $ distribution after the final selection. The black symbols with error bars show data, while the filled histograms represent the SM backgrounds. Signal examples for SSM W' bosons with masses of 0.6, 1.0, 4.0, and 5.0 TeV are shown with the open histograms. (Right) The integral transverse mass distribution, where the value in each bin is equal to the number of events with transverse mass equal to or greater than the left of the bin. The lower panels show the ratio of data to prediction, and the gray band represents the systematic uncertainties. |
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Figure 3-a:
The $ {m_{\mathrm {T}}} $ distribution after the final selection. The black symbols with error bars show data, while the filled histograms represent the SM backgrounds. Signal examples for SSM W' bosons with masses of 0.6, 1.0, 4.0, and 5.0 TeV are shown with the open histograms. The lower panel shows the ratio of data to prediction, and the gray band represents the systematic uncertainties. |
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Figure 3-b:
The integral transverse mass distribution, where the value in each bin is equal to the number of events with transverse mass equal to or greater than the left of the bin. The lower panel shows the ratio of data to prediction, and the gray band represents the systematic uncertainties. |
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Figure 4:
Distribution of $ {p_{\mathrm {T}}} ^{{\tau}}$ in the control region. The black symbols with error bars show the data, while the histograms represent the SM backgrounds. The lower panel shows the ratio of data to prediction. |
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Figure 5:
Expected (black dashed line) and observed (black solid line) 95% CL upper limits on the cross section for the production of SSM W' boson. The shaded bands around the expected limit represent the one and two standard deviation (s.d.) uncertainty intervals. The NNLO theoretical cross section with the corresponding PDF uncertainty band is also shown. |
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Figure 6:
Expected (black dashed line) and observed (black solid line) 95% CL upper limits on the ratio of couplings as a function of the W' boson mass. The values above the observed limit contour are excluded. The shaded bands around the expected limit represent the one and two standard deviation (s.d.) uncertainty intervals. |
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Figure 7:
Left: The width of the W' boson as a function of $M_{{\mathrm {W}'}}$ and mixing angle $\cot\theta _{\mathrm {E}}$ in the NUGIM G(221) framework. Right: Expected (black dashed line) and observed (black solid line) 95% CL upper limits on the mixing angle $\cot\theta _{\mathrm {E}}$ as a function of the W' boson mass. The region left of the solid line is excluded. The shaded bands represent the one and two standard deviation (s.d.) uncertainty bands. |
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Figure 7-a:
The width of the W' boson as a function of $M_{{\mathrm {W}'}}$ and mixing angle $\cot\theta _{\mathrm {E}}$ in the NUGIM G(221) framework. |
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Figure 7-b:
Expected (black dashed line) and observed (black solid line) 95% CL upper limits on the mixing angle $\cot\theta _{\mathrm {E}}$ as a function of the W' boson mass. The region left of the solid line is excluded. The shaded bands represent the one and two standard deviation (s.d.) uncertainty bands. |
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Figure 8:
Expected (black dashed line) and observed (black solid line) 95% CL model-independent upper limits on the product of cross section, branching fraction, and acceptance for a resonance decaying into the $ {\tau} {\nu}$ channel. The shaded bands represent the one and two standard deviation (s.d.) uncertainty bands. |
Tables | |
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Table 1:
Expected yields for the signal and background events compared to the measured event yields in data, for three regions of ${m_{\mathrm {T}}}$. Also shown are the total systematic uncertainties in the estimate of the event numbers. |
Summary |
A search for new physics in final states with a hadronically decaying $\tau$ lepton and missing transverse momentum has been performed by the CMS experiment, using proton-proton collision data at the center-of-mass energy $\sqrt{s} = $ 13 TeV with an integrated luminosity of 35.9 fb$^{-1}$. No significant excess compared to the standard model expectation is observed in the transverse mass of the tau and missing transverse momentum. A sequential standard model W' boson is excluded in the mass range 0.4 $ < M_{\mathrm{W'}} < $ 4.0 TeV at 95% confidence level. Couplings that are weaker than assumed in the sequential standard model can be excluded down to values of $ 7 \times 10^{-2} $ for $M_{\mathrm{W'}} = $ 1 TeV. Within the nonuniversal gauge interaction SU(2)xSU(2)xU(1) model, the lower limit on the W' boson mass depends on the coupling constant and varies from 1.7 to 3.9 TeV at 95% confidence level. For $\cot\theta_{\mathrm{E}} > $ 1, these results obtained in the tau channel provide the most stringent constraints on this model to date. In addition, a model-independent limit is provided allowing the results to be interpreted in other models giving the same final state with similar kinematic distributions. |
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Compact Muon Solenoid LHC, CERN |