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| CMS-TOP-15-001 ; CERN-EP-2017-012 | ||
| Measurement of the top quark mass using single top quark events in proton-proton collisions at $\sqrt{s}= $ 8 TeV | ||
| CMS Collaboration | ||
| 7 March 2017 | ||
| EPJC 77 (2017) 354 | ||
| Abstract: A measurement of the top quark mass is reported in events containing a single top quark produced via the electroweak $t$ channel. The analysis is performed using data from proton-proton collisions collected with the CMS detector at the LHC at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 19.7 fb$^{-1}$. The top quark is reconstructed from its decay to a W boson and a b quark, with the W boson decaying leptonically to a muon and a neutrino. The specific topology and kinematic properties of single top quark events in the $t$ channel are used to enhance the purity of the sample, suppressing the contribution from top quark pair production. A fit to the invariant mass distribution of reconstructed top quark candidates yields a value of the top quark mass of 172.95 $\pm$ 0.77 (stat) $^{+0.97}_{-0.93}$ (syst) GeV. This result is in agreement with the current world average, and represents the first measurement of the top quark mass in event topologies not dominated by top quark pair production. | ||
| Links: e-print arXiv:1703.02530 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
The dominant Feynman diagrams for single top quark production in the $t$ channel. |
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Figure 1-a:
One of the dominant Feynman diagrams for single top quark production in the $t$ channel. |
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Figure 1-b:
One of the dominant Feynman diagrams for single top quark production in the $t$ channel. |
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Figure 2:
Distribution of the light-quark jet pseudorapidity (left) and of the muon charge (right) for all top quark candidates in the muonic decay channel. Points with error bars represent data, stacked histograms show expected contributions from Monte Carlo simulation. The hatched area represents the uncertainty on the Monte Carlo predictions associated to the finite size of the samples and their normalization, and the integrated luminosity. |
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Figure 2-a:
Distribution of the light-quark jet pseudorapidity for all top quark candidates in the muonic decay channel. Points with error bars represent data, stacked histograms show expected contributions from Monte Carlo simulation. The hatched area represents the uncertainty on the Monte Carlo predictions associated to the finite size of the samples and their normalization, and the integrated luminosity. |
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Figure 2-b:
Distribution of the muon charge for all top quark candidates in the muonic decay channel. Points with error bars represent data, stacked histograms show expected contributions from Monte Carlo simulation. The hatched area represents the uncertainty on the Monte Carlo predictions associated to the finite size of the samples and their normalization, and the integrated luminosity. |
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Figure 3:
Reconstructed $\mu \nu \mathrm{ b } $ invariant mass distribution for data (points with error bars) and Monte Carlo events (stacked histograms). Left: initial selection; right: final selection after the charge and light-quark jet pseudorapidity requirements. The ratio of the observed number of events in data to the number predicted by simulation is shown in the lower plots. The hatched area represents the uncertainty on the Monte Carlo predictions associated to the finite size of the samples and their normalization, and the integrated luminosity. |
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Figure 3-a:
Reconstructed $\mu \nu \mathrm{ b } $ invariant mass distribution for data (points with error bars) and Monte Carlo events (stacked histograms): initial selection after the charge and light-quark jet pseudorapidity requirements. The ratio of the observed number of events in data to the number predicted by simulation is shown in the lower plots. The hatched area represents the uncertainty on the Monte Carlo predictions associated to the finite size of the samples and their normalization, and the integrated luminosity. |
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Figure 3-b:
Reconstructed $\mu \nu \mathrm{ b } $ invariant mass distribution for data (points with error bars) and Monte Carlo events (stacked histograms): final selection after the charge and light-quark jet pseudorapidity requirements. The ratio of the observed number of events in data to the number predicted by simulation is shown in the lower plots. The hatched area represents the uncertainty on the Monte Carlo predictions associated to the finite size of the samples and their normalization, and the integrated luminosity. |
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Figure 4:
Reconstructed $\mu \nu \mathrm{ b } $ invariant mass from Monte Carlo simulated events for single top quark $t$ channel (left) and ${\mathrm{ t } {}\mathrm{ \bar{t} } }$ (right). The continuous lines show the results of fits to Crystal Ball shapes. |
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Figure 4-a:
Reconstructed $\mu \nu \mathrm{ b } $ invariant mass from Monte Carlo simulated events for single top quark $t$ channel. The continuous lines show the results of fits to Crystal Ball shapes. |
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Figure 4-b:
Reconstructed $\mu \nu \mathrm{ b } $ invariant mass from Monte Carlo simulated events for ${\mathrm{ t } {}\mathrm{ \bar{t} } }$. The continuous lines show the results of fits to Crystal Ball shapes. |
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Figure 5:
Mass calibration from fits to samples with different generated top quark mass. Left: fit results as a function of the generated top quark mass. The straight line shows the result of a linear fit to the chosen top quark mass values. Right: mass correction, as a function of the fitted top quark mass (straight line). The shaded grey area represents the associated systematic uncertainty. |
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Figure 5-a:
Mass calibration from fits to samples with different generated top quark mass: fit results as a function of the generated top quark mass. The straight line shows the result of a linear fit to the chosen top quark mass values. |
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Figure 5-b:
Mass calibration from fits to samples with different generated top quark mass: mass correction, as a function of the fitted top quark mass (straight line). The shaded grey area represents the associated systematic uncertainty. |
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Figure 6:
Reconstructed $\mu \nu \mathrm{ b } $ invariant mass for non-top-quark background events, from Monte Carlo simulation. Left: before final selection; right: after final selection. The continuous lines show the results of fits to Novosibirsk functions. |
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Figure 6-a:
Reconstructed $\mu \nu \mathrm{ b } $ invariant mass for non-top-quark background events, from Monte Carlo simulation before final selection. The continuous lines show the results of fits to Novosibirsk functions. |
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Figure 6-b:
Reconstructed $\mu \nu \mathrm{ b } $ invariant mass for non-top-quark background events, from Monte Carlo simulation after final selection. The continuous lines show the results of fits to Novosibirsk functions. |
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Figure 7:
Result of the fit to the reconstructed $\mu \nu \mathrm{ b } $ invariant mass. Left: Monte Carlo simulation; right: data. In each plot, the solid line represents the result of the full fit; the dotted line shows the non-top-quark component, while the dashed line shows the sum of all background components. |
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Figure 7-a:
Result of the fit to the reconstructed $\mu \nu \mathrm{ b } $ invariant mass: Monte Carlo simulation. The solid line represents the result of the full fit; the dotted line shows the non-top-quark component, while the dashed line shows the sum of all background components. |
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Figure 7-b:
Result of the fit to the reconstructed $\mu \nu \mathrm{ b } $ invariant mass: data. The solid line represents the result of the full fit; the dotted line shows the non-top-quark component, while the dashed line shows the sum of all background components. |
| Tables | |
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Table 1:
Systematic uncertainties in the top quark mass. |
| Summary |
| The top quark mass is measured in a sample enriched in events with a single top quark for the first time. Top quarks are reconstructed from decays to a W boson and a b quark, with the W boson decaying to a muon and a neutrino. In the final sample, events with a top quark from single production in the $t$-channel account for 73% of the total number of events with a top quark. The measurement is obtained from a fit to the distribution of the reconstructed mass of top quark candidates, where the $t$-channel single top quark component is modelled separately from the contribution of other top quark production channels. The measured value is $m_{\mathrm{ t }} =$ 172.95 $\pm$ 0.77 (stat) $^{+0.97}_{-0.93}$ (syst) GeV. This is in agreement with the current combination of Tevatron and LHC results, 173.34 $\pm$ 0.27 (stat) $\pm$ 0.71 (syst) GeV, which is based on measurements using $\mathrm{ t \bar{t} }$ events. |
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