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| CMS-PAS-B2G-17-003 | ||
| Search for vector-like quark pair production $\mathrm{T\bar{T}}(\mathrm{Y\bar{Y}})\rightarrow\mathrm{bWbW}$ using kinematic reconstruction in lepton+jets final states at $\sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| May 2017 | ||
| Abstract: A search is presented for the pair production of vector-like quarks, $\mathrm{T\bar{T}}$ or $\mathrm{Y\bar{Y}}$, with an electric charge of either 2/3$|\mathrm{e}|\mathrm{(T)}$ or -4/3$|\mathrm{e}|\mathrm{(Y)}$ in proton-proton collisions at $\sqrt{s} = $ 13 TeV at the LHC. The data were collected by the CMS experiment during the 2016 LHC run, and correspond to an integrated luminosity of 35.8 fb$^{-1}$. The $\mathrm{T(Y)}$ quarks are assumed to decay exclusively to a W boson and a b quark. The search is carried out using events with a single isolated electron or muon, large missing transverse energy and at least four jets with large transverse momenta. In the search a kinematic reconstruction of the final state is performed. Under the assumption of strong pair production of vector-like quarks and 100% branching fractions to bW, an observed (expected) lower limit of 1295 (1275) GeV at 95% CL is set on the T(Y) quark mass. | ||
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Links:
CDS record (PDF) ;
inSPIRE record ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, PLB 779 (2018) 82. The superseded preliminary plots can be found here. |
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| Figures & Tables | Summary | Additional Figures | References | CMS Publications |
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| Figures | |
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Figure 1:
Reconstructed mass spectra for e+jets (top) and $\mu $+jets (middle) channel and their sum (bottom). Errors are statistical only. |
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Figure 1-a:
Reconstructed mass spectra for the e+jets channel. Errors are statistical only. |
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Figure 1-b:
Reconstructed mass spectra for the $\mu $+jets channel. Errors are statistical only. |
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Figure 1-c:
Reconstructed mass spectra for the sum of the e+jets and $\mu $+jets channels. Errors are statistical only. |
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Figure 2:
Reconstructed mass spectra for the sum of the e+jets and $\mu $+jets channels in logarithmic scale for $M_{\mathrm {reco}}$ (top) and logarithmic vertical scale (bottom). Errors are statistical only. |
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Figure 2-a:
Reconstructed mass spectra for the sum of the e+jets and $\mu $+jets channels in logarithmic scale for $M_{\mathrm {reco}}$. Errors are statistical only. |
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Figure 2-b:
Reconstructed mass spectra for the sum of the e+jets and $\mu $+jets channels in logarithmic vertical scale. Errors are statistical only. |
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Figure 3:
Reconstructed mass spectra for the sum of the selected e+jets and $\mu $+jets events for the "noWtag'' category of events (top), and for the "Wtag'' category of events (bottom). Errors are statistical only. |
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Figure 3-a:
Reconstructed mass spectra for the sum of the selected e+jets and $\mu $+jets events for the "noWtag'' category of events. Errors are statistical only. |
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Figure 3-b:
Reconstructed mass spectra for the sum of the selected e+jets and $\mu $+jets events for the "Wtag'' category of events. Errors are statistical only. |
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Figure 4:
Exclusion limits obtained using W-tagged category of events only (top) and post-fit distribution of the reconstructed mass, $M_{\mathrm {reco}}$ (bottom). Shaded band on the histogram shows statistical and systematic uncertainties. |
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Figure 4-a:
Exclusion limits obtained using W-tagged category of events only. Shaded band on the histogram shows statistical and systematic uncertainties. |
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Figure 4-b:
Exclusion limits obtained using post-fit distribution of the reconstructed mass, $M_{\mathrm {reco}}$. Shaded band on the histogram shows statistical and systematic uncertainties. |
| Tables | |
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Table 1:
Background processes, number of data events observed and background events predicted for the integrated luminosity of data. The errors on the MC yields are statistical only. |
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Table 2:
Selection efficiencies for $\mathrm {T \bar{T}}$ MC assuming $\mathcal {B}(\mathrm {T} \rightarrow \mathrm {bW}) = $ 100% and expected signal events after the final selection, for the integrated luminosity of data. The errors are statistical only. |
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Table 3:
Variations of the yield of the selected MC events related to shape systematic uncertainties for a signal with a T quark mass of 1200 GeV and background (BG). |
| Summary |
| The results of a search for vector-like quarks $\mathrm{T}$ or $\mathrm{Y}$ that are pair produced in pp interactions at $\sqrt{s}= $ 13 TeV and decay exclusively to bW have been presented. Events were selected in which one of the W bosons decays to leptons and the other to a quark-antiquark pair. The selection required a muon or electron, significant missing transverse energy, and at least four jets. A kinematic fit assuming $\mathrm{T\bar{T}}$ or $\mathrm{Y\bar{Y}}$ production was performed and for every event a candidate $\mathrm{T}/\mathrm{Y}$-quark mass $M_{\text{reco}}$ was reconstructed. No significant deviations from the standard model expectations have been found in the $M_{\text{reco}}$ distribution. Upper limits have been set on the production cross section of such $\mathrm{T}/\mathrm{Y}$ quarks as a function of their mass. By comparing with the predicted cross section for vector like quark pair production, the strong pair production of $\mathrm{T}/\mathrm{Y}$ quarks is excluded at 95%CL for masses below 1295 GeV (1275 GeV expected). This is the most restrictive result for T(Y) VLQ pair production at the time of this publication. The search is equally sensitive to any kind of quarks decaying to the same channel. The results can be interpreted as upper limits on the production cross section times the branching fraction of decay to bW. |
| Additional Figures | |
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Additional Figure 1:
Distributions of $\mathrm {T\bar{T}}$ mass for the $e$+jets (top) and $\mu $+jets (middle) channel and their sum (bottom). Errors are statistical only. |
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Additional Figure 1-a:
Distributions of $\mathrm {T\bar{T}}$ mass for the $e$+jets channal. Errors are statistical only. |
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Additional Figure 1-b:
Distributions of $\mathrm {T\bar{T}}$ mass for the $\mu $+jets channel. Errors are statistical only. |
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Additional Figure 1-c:
Distributions of $\mathrm {T\bar{T}}$ mass for the sum of the $e$+jets and $\mu $+jets channels. Errors are statistical only. |
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Additional Figure 2-a:
Display of the data event with highest reconstructed mass of 2775 GeV for the hypothesis $\mathrm {T\bar{T}}\rightarrow \mathrm {bWbW} \rightarrow \mathrm {e}\nu 4 \text{jets} $ |
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Additional Figure 2-b:
Display of the data event with highest reconstructed mass of 2775 GeV for the hypothesis $\mathrm {T\bar{T}}\rightarrow \mathrm {bWbW} \rightarrow \mathrm {e}\nu 4 \text{jets} $ |
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Additional Figure 2-c:
Display of the data event with highest reconstructed mass of 2775 GeV for the hypothesis $\mathrm {T\bar{T}}\rightarrow \mathrm {bWbW} \rightarrow \mathrm {e}\nu 4 \text{jets} $ |
| If we assume the the existence of a heavy resonance, decaying to a pair of VLQs (like, for example $\mathrm{ Z' \rightarrow T\bar{T} }$), we can consider the mass spectrum M($\mathrm{T\bar{T}}$) as another signal distribution, which permits to search for heavy resonances. This distribution is shown in Additional Fig.1 for selected events. We do not observe any significant excess of data over the expected background. |
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