CMS-PAS-B2G-16-006

CMS-PAS-B2G-16-006
Search for singly-produced vector-like quarks decaying into a W boson and a bottom quark using the single lepton final state
CMS Collaboration
July 2016

Abstract: We present a search for the single production of a heavy vector-like quark, decaying into a W boson and a b quark. The search is performed using the data sample of pp collisions at a center of mass energy of $\sqrt{s} = $ 13 TeV collected by the CMS experiment at the Large Hadron Collider in 2015. The dataset used in the analysis corresponds to 2.3 fb$^{-1}$ of integrated luminosity. The search is carried out using events containing one electron or muon, at least one b-tagged jet with large transverse momentum, at least one jet in the forward region of the detector, and missing transverse energy. No excess over the standard model predictions is observed. Upper bounds are placed on the production cross section of heavy top quark partners, T quark with a charge of 2/3e and Y quark with a charge of -4/3e. The results are also interpreted as limits on the mass of the vector-like quark and its coupling to the W boson and the b quark. T quarks with masses below 1.73 TeV are excluded at 95% C.L. assuming a unit coupling and a $ \mathcal{B}(\mathrm{T \rightarrow Wb}) =$ 0.5, while the expected limit is 1.42 TeV. Y quarks with coupling of 0.5 and $\mathcal{B}(\mathrm{ Y \rightarrow Wb}) =$ 1 are excluded below 1.40 TeV, whereas the expected limit is 0.99 TeV.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; These preliminary results are superseded in this paper, PLB 772 (2017) 634. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Leading order Feynman diagram for singly produced Y and T quarks.
png pdf	Figure 2-a: Kinematic distributions in the ${\mathrm{ t } \mathrm{ \bar{t} } } $-enriched control sample.
png pdf	Figure 2-b: Kinematic distributions in the ${\mathrm{ t } \mathrm{ \bar{t} } } $-enriched control sample.
png pdf	Figure 3-a: Kinematic distributions in the W+jets-enriched control sample.
png pdf	Figure 3-b: Kinematic distributions in the W+jets-enriched control sample.
png pdf	Figure 4: The invariant mass $M_{\text {inv}}$ distribution after the fit. In the last bin the data overflow event is an electron channel event with a mass of 2215 GeV.
png pdf	Figure 5: Expected and observed limits on the single VLQ production cross section together with the 1- and 2- sigma uncertainty bands.
png pdf	Figure 6: Expected and observed limits on the electroweak coupling of the Y quark as a function of its mass. The region above the observed limit is excluded in this analysis at 95% C.L.
png pdf	Figure 7: Expected and observed limits on the electroweak coupling of the T quark as a function of its mass. The region above the observed limit is excluded in this analysis at 95% C.L.

Tables
png pdf	Table 1: Summary of the systematic uncertainties for the background MC and signal samples.
png pdf	Table 2: Data, background and signal ($m(\mathrm{Y}) =$ 1000 GeV mass point with the NLO cross section [26]) pre-fit event yields corresponding to 2.3fb$^{-1}$ of integrated luminosity. Percentage numbers in the signal column indicates the signal acceptance efficiency. The error on the backgrounds includes both pre-fit statistical and systematic uncertainties.
png pdf	Table 3: Expected and observed upper limits on the single VLQ production cross section ($\sigma \times \mathcal{B}(\mathrm{ Q \rightarrow Wb}) =$100%)

Summary

The results for the single production of the vector-like quark decaying exclusively into a W boson and a b quark are presented. The search is performed in the electron/muon + jets channels. The mass of the vector-like quark is reconstructed by forming the invariant mass of the leading b-jet, electron or muon and reconstructed neutrino in the event, and the fit to the invariant mass spectrum is performed. No evidence of an excess due to new physics is observed, and 95% C.L. upper limits are set on the single vector-like production cross section in the mass range from 700 to 1800 GeV. The results are also interpreted as limits on the mass of the vector-like quark and its coupling to the W boson and the b quark. T quarks with masses below 1.73 TeV are excluded at 95% C.L. assuming a unit coupling and a $\mathcal{B}(\mathrm{ T \rightarrow Wb}) =$ 0.5, while the expected limit is 1.42 TeV. Y quarks with coupling of 0.5 and a $\mathcal{B}(\mathrm{ Y \rightarrow Wb}) =$ 1 are excluded below 1.40 TeV, whereas the expected limit is 0.99 TeV.

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