A search for a heavy resonance decaying into a top quark and a W boson in proton-proton collisions at $\sqrt{s} =$ 13 TeV is presented. The data analyzed were recorded with the CMS detector at the LHC and correspond to an integrated luminosity of 138 fb$^{-1}$. The top quark is reconstructed as a single jet and the W boson, from its decay into an electron or muon and the corresponding neutrino. A top quark tagging technique based on jet clustering with a variable distance parameter and simultaneous jet grooming is used to identify jets from the collimated top quark decay. The results are interpreted in the context of two benchmark models, where the heavy resonance is either an excited bottom quark b$^*$ or a vector-like quark B. A statistical combination with an earlier search by the CMS Collaboration in the all-hadronic final state is performed to place upper cross section limits on these two models. The new analysis extends the lower range of resonance mass probed from 1.4 down to 0.7 TeV. For left-handed, right-handed, and vector-like couplings, b$^*$ masses up to 3.0, 3.0, and 3.2 TeV are excluded at 95% confidence level, respectively. The observed upper limits represent the most stringent constraints on the b$^*$ model to date.
Distributions of MtW in the 1b category. The data are shown by filled markers, where the horizontal bars indicate the bin widths. The individual background contributions are given by filled histograms. The expected signal for a LH b* with mb∗ = 2.4 TeV is shown by a dashed line. The shaded region is the uncertainty in the total background estimate. The lower panel shows the ratio of data to the background estimate, with the total uncertainty on the predicted background displayed as the gray band.
Distributions of MtW in the 2b category. The data are shown by filled markers, where the horizontal bars indicate the bin widths. The individual background contributions are given by filled histograms. The expected signal for a LH b* with mb∗ = 2.4 TeV is shown by a dashed line. The shaded region is the uncertainty in the total background estimate. The lower panel shows the ratio of data to the background estimate, with the total uncertainty on the predicted background displayed as the gray band.
Upper limits on the production cross section times branching fraction of the b* LH hypothesis at a 95% CL. Dashed colored lines show the expected limits from the l+jets and all-hadronic channels, where the latter start at resonance masses of 1.4 TeV. The observed and expected limits from the combination are shown as solid and dashed black lines, respectively. The green and yellow bands show the 68 and 95% confidence intervals on the combined expected limits.
A search for the pair production of heavy vector-like partners T and B of the top and bottom quarks has been performed by the CMS experiment at the CERN LHC using proton-proton collisions at $\sqrt{s} =$ 13 TeV. The data sample was collected in 2016 and corresponds to an integrated luminosity of 35.9 fb$^{-1}$. Final states studied for $\mathrm{T\overline{T}}$ production include those where one of the T quarks decays via T $\to$ tZ and the other via T $\to$ bW, tZ, or tH, where H is a Higgs boson. For the $\mathrm{B\overline{B}}$ case, final states include those where one of the B quarks decays via B $\to$ bZ and the other B $\to$ tW, bZ, or bH. Events with two oppositely charged electrons or muons, consistent with coming from the decay of a Z boson, and jets are investigated. The number of observed events is consistent with standard model background estimations. Lower limits at 95% confidence level are placed on the masses of the T and B quarks for a range of branching fractions. Assuming 100% branching fractions for T $\to$ tZ, and B $\to$ bZ, T and B quark mass values below 1280 and 1130 GeV, respectively, are excluded.
The $S_{\rm T}$ distribution for group A before fitting.
The $S_{\rm T}$ distribution for group B before fitting.
The $S_{\rm T}$ distribution for group C before fitting.
A search is presented for the pair production of heavy vector-like quarks, $T\bar T$ or $B\bar B$, that decay into final states with jets and no reconstructed leptons. Jets in the final state are classified using a deep neural network as arising from hadronically decaying $W/Z$ bosons, Higgs bosons, top quarks, or background. The analysis uses data from the ATLAS experiment corresponding to 36.1 fb$^{-1}$ of proton-proton collisions with a center-of-mass energy of $\sqrt{s} = 13$ TeV delivered by the Large Hadron Collider in 2015 and 2016. No significant deviation from the Standard Model expectation is observed. Results are interpreted assuming the vector-like quarks decay into a Standard Model boson and a third-generation-quark, $T\rightarrow Wb,Ht,Zt$ or $B\rightarrow Wt,Hb,Zb$, for a variety of branching ratios. At 95% confidence level, the observed (expected) lower limit on the vector-like $B$-quark mass for a weak-isospin doublet ($B, Y$) is 950 (890) GeV, and the lower limits on the masses for the pure decays $B\rightarrow Hb$ and $T\rightarrow Ht$, where these results are strongest, are 1010 (970) GeV and 1010 (1010) GeV, respectively.
Expected and observed upper limits at the 95% CL on the $T\bar T$ cross section as a function of $T$ mass under the assumption BR($T\to Ht$)=1.
Expected and observed upper limits at the 95% CL on the $B\bar B$ cross section as a function of $B$ mass under the assumption BR($B\to Hb$)=1.
Expected and observed upper limits at the 95% CL on the $B\bar B$ cross section as a function of $B$ mass under the assumption of a weak-isospin doublet.
A search is presented for the pair production of heavy vector-like $B$ quarks, primarily targeting $B$ quark decays into a $W$ boson and a top quark. The search is based on $36.1$ $fb^{-1}$ of $pp$ collisions at $\sqrt{s}$ = 13 TeV recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. Data are analysed in the lepton-plus-jets final state, characterised by a high-transverse-momentum isolated electron or muon, large missing transverse momentum, and multiple jets, of which at least one is $b$-tagged. No significant deviation from the Standard Model expectation is observed. The 95% confidence level lower limit on the $B$ mass is 1350 GeV assuming a 100% branching ratio to $Wt$. In the SU(2) singlet scenario, the lower mass limit is 1170 GeV. This search is also sensitive to a heavy vector-like $B$ quark decaying into other final states ($Zb$ and $Hb$) and thus mass limits on $B$ production are set as a function of the decay branching ratios. The 100% branching ratio limits are found to be also applicable to heavy vector-like $X$ production, with charge $+$5/3, that decay into $Wt$.
The hadronically decaying VLB candidate mass in the RECOSR region after the maximum likelihood fit in the two signal regions overlayed with the pre-fit VLB signal
The BDT discriminant in the BDTSR region after the maximum likelihood fit in the two signal regions overlayed with the pre-fit VLB signal
Expected and observed upper limits at the 95% CL on the BB cross section as a function of B quark mass under the assumption of BR(B->Wt)=1.
A search is presented for the pair production of heavy vector-like $T$ and $B$ quarks, primarily targeting the $T$ quark decays to a $W$ boson and a $b$-quark. The search is based on $36.1$ fb$^{-1}$ of $pp$ collisions at $\sqrt{s}$ = 13 TeV recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. Data are analysed in the lepton-plus-jets final state, including at least one $b$-tagged jet and a large-radius jet identified as originating from the hadronic decay of a high-momentum $W$ boson. No significant deviation from the Standard Model expectation is observed in the reconstructed $T$ mass distribution. The observed 95% confidence level lower limit on the $T$ mass are 1350 GeV assuming 100% branching ratio to $Wb$. In the SU(2) singlet scenario, the lower mass limit is 1170 GeV. This search is also sensitive to a heavy vector-like $B$ quark decaying to $Wt$ and other final states. The results are thus reinterpreted to provide a 95% confidence level lower limit on the $B$ quark mass at 1250 GeV assuming 100% branching ratio to $Wt$; in the SU(2) singlet scenario, the limit is 1080 GeV. Mass limits on both $T$ and $B$ production are also set as a function of the decay branching ratios. The 100% branching ratio limits are found to be applicable to heavy vector-like $Y$ and $X$ production that decay to $Wb$ and $Wt$, respectively.
The leptonic VLQ candidate mass distributions in the signal region after the maximum likelihood fit in the signal region and control region.
Expected and observed upper limits at the 95% CL on the TT cross section as a function of T quark mass under the assumption of BR(T->Wb)=1.
Expected and observed upper limits at the 95% CL on the TT cross section as a function of T quark mass for an SU(2) singlet T.
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