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| CMS-PAS-TOP-18-005 | ||
| Measurement of the top quark pair production cross section in the dilepton channel including a $\tau$ lepton in proton-proton collisions at $\sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| August 2019 | ||
| Abstract: The cross section of the top quark pair production process $\mathrm{t\overline{t}}\rightarrow (\ell\nu_{\ell})(\tau_{\mathrm{h}}\nu_{\tau})\mathrm{b\overline{b}}$ is measured, where the $\tau_{\mathrm{h}}$ refers to the hadronic decays of the $\tau$ lepton, and $\ell=$ e, $\mu$. The data sample corresponds to an integrated luminosity of 35.9 fb$^{-1}$ and was collected in 2016 by the CMS detector in proton-proton collisions at $\sqrt{s}= $ 13 TeV. The measured cross section is $\sigma_{\mathrm{t\overline{t}}} = $ 781 $\pm$ 7 (stat) $\pm$ 62 (syst) $\pm$ 20 (lumi) pb. The ratio of the partial width $\Gamma(\mathrm{t}\rightarrow\tau\nu_{\tau}\mathrm{b})$ to the total width is measured to be 0.1050 $\pm$ 0.0009 (stat) $\pm$ 0.0071 (syst). | ||
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Links:
CDS record (PDF) ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, JHEP 02 (2020) 191. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
The pre-fit $ {\tau _\mathrm {h}} $ ${p_{\mathrm {T}}}$ distributions for events of the $\mathrm{e} {\tau _\mathrm {h}} $ (left) and $\mu {\tau _\mathrm {h}} $ (right) final states. Distributions obtained from data (full circle) are compared with simulation (shaded area). The last bin includes the overflow of the $ {p_{\mathrm {T}}} $ distribution. The simulated contributions are normalized to the SM predicted values. The main processes are shown: the signal ($\mathrm{e} {\tau _\mathrm {h}} $ and $\mu {\tau _\mathrm {h}} $ final states), the other ${\mathrm{t} \mathrm{\bar{t}}}$ processes lumped together, single top quark (mainly $\mathrm{t} \mathrm{W} $), DY processes (mainly the $\tau _{\ell} {\tau _\mathrm {h}} $ decay), W+jets, dibosons and multijet. The ratio of the data to the total SM prediction is shown in the lower panel. The vertical bars on the data indicate the statistical uncertainties, the gray hatched band indicates the systematic uncertainties and the statistical uncertainties of all simulated samples. |
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Figure 1-a:
The pre-fit $ {\tau _\mathrm {h}} $ ${p_{\mathrm {T}}}$ distributions for events of the $\mathrm{e} {\tau _\mathrm {h}} $ (left) and $\mu {\tau _\mathrm {h}} $ (right) final states. Distributions obtained from data (full circle) are compared with simulation (shaded area). The last bin includes the overflow of the $ {p_{\mathrm {T}}} $ distribution. The simulated contributions are normalized to the SM predicted values. The main processes are shown: the signal ($\mathrm{e} {\tau _\mathrm {h}} $ and $\mu {\tau _\mathrm {h}} $ final states), the other ${\mathrm{t} \mathrm{\bar{t}}}$ processes lumped together, single top quark (mainly $\mathrm{t} \mathrm{W} $), DY processes (mainly the $\tau _{\ell} {\tau _\mathrm {h}} $ decay), W+jets, dibosons and multijet. The ratio of the data to the total SM prediction is shown in the lower panel. The vertical bars on the data indicate the statistical uncertainties, the gray hatched band indicates the systematic uncertainties and the statistical uncertainties of all simulated samples. |
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Figure 1-b:
The pre-fit $ {\tau _\mathrm {h}} $ ${p_{\mathrm {T}}}$ distributions for events of the $\mathrm{e} {\tau _\mathrm {h}} $ (left) and $\mu {\tau _\mathrm {h}} $ (right) final states. Distributions obtained from data (full circle) are compared with simulation (shaded area). The last bin includes the overflow of the $ {p_{\mathrm {T}}} $ distribution. The simulated contributions are normalized to the SM predicted values. The main processes are shown: the signal ($\mathrm{e} {\tau _\mathrm {h}} $ and $\mu {\tau _\mathrm {h}} $ final states), the other ${\mathrm{t} \mathrm{\bar{t}}}$ processes lumped together, single top quark (mainly $\mathrm{t} \mathrm{W} $), DY processes (mainly the $\tau _{\ell} {\tau _\mathrm {h}} $ decay), W+jets, dibosons and multijet. The ratio of the data to the total SM prediction is shown in the lower panel. The vertical bars on the data indicate the statistical uncertainties, the gray hatched band indicates the systematic uncertainties and the statistical uncertainties of all simulated samples. |
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Figure 2:
Comparison of the shape of the distributions (normalized to unity) of the transverse mass between the lepton and ${{p_{\mathrm {T}}} ^\text {miss}}$, for the signal (${\mathrm{t} \mathrm{\bar{t}}} \rightarrow \ell \nu _{\ell} {\tau _\mathrm {h}} \nu _{\tau} \mathrm{b} \mathrm{\bar{b}} $) and the main background of misidentified $ {\tau _\mathrm {h}} $ (${\mathrm{t} \mathrm{\bar{t}}} \rightarrow \ell \nu _{\ell} \mathrm{q} \mathrm{\bar{q}} ' \mathrm{b} \mathrm{\bar{b}} $) in simulated ${\mathrm{t} \mathrm{\bar{t}}}$ events. |
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Figure 3:
The pre-fit transverse mass distributions between lepton and ${{p_{\mathrm {T}}} ^\text {miss}}$, $M_{\mathrm {T}}$, in the signal-like (top) and background-like (bottom) event categories for the $\mathrm{e} {\tau _\mathrm {h}} $ (left) and $\mu {\tau _\mathrm {h}} $ (right) final states. Distributions obtained from data (full circle) are compared with simulation (shaded area). The last bin includes the overflow of the $M_{\mathrm {T}}$ distribution. The simulated contributions are normalized to the SM predicted values. The main processes are shown: the signal ($e {\tau _\mathrm {h}} $ and $\mu {\tau _\mathrm {h}} $ final states), the other ${\mathrm{t} \mathrm{\bar{t}}}$ processes lumped together, single top quark (mainly $\mathrm{t} \mathrm{W} $), DY processes (mainly the $\tau _{\ell} {\tau _\mathrm {h}} $ decay), W+jets, dibosons and multijet. The ratio of the data to the total SM prediction is shown in the lower panel. The vertical bars on the data indicate the statistical uncertainties, the hatched band indicates the systematic uncertainties and the statistical uncertainties of all simulated samples. |
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Figure 3-a:
The pre-fit transverse mass distributions between lepton and ${{p_{\mathrm {T}}} ^\text {miss}}$, $M_{\mathrm {T}}$, in the signal-like (top) and background-like (bottom) event categories for the $\mathrm{e} {\tau _\mathrm {h}} $ (left) and $\mu {\tau _\mathrm {h}} $ (right) final states. Distributions obtained from data (full circle) are compared with simulation (shaded area). The last bin includes the overflow of the $M_{\mathrm {T}}$ distribution. The simulated contributions are normalized to the SM predicted values. The main processes are shown: the signal ($e {\tau _\mathrm {h}} $ and $\mu {\tau _\mathrm {h}} $ final states), the other ${\mathrm{t} \mathrm{\bar{t}}}$ processes lumped together, single top quark (mainly $\mathrm{t} \mathrm{W} $), DY processes (mainly the $\tau _{\ell} {\tau _\mathrm {h}} $ decay), W+jets, dibosons and multijet. The ratio of the data to the total SM prediction is shown in the lower panel. The vertical bars on the data indicate the statistical uncertainties, the hatched band indicates the systematic uncertainties and the statistical uncertainties of all simulated samples. |
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Figure 3-b:
The pre-fit transverse mass distributions between lepton and ${{p_{\mathrm {T}}} ^\text {miss}}$, $M_{\mathrm {T}}$, in the signal-like (top) and background-like (bottom) event categories for the $\mathrm{e} {\tau _\mathrm {h}} $ (left) and $\mu {\tau _\mathrm {h}} $ (right) final states. Distributions obtained from data (full circle) are compared with simulation (shaded area). The last bin includes the overflow of the $M_{\mathrm {T}}$ distribution. The simulated contributions are normalized to the SM predicted values. The main processes are shown: the signal ($e {\tau _\mathrm {h}} $ and $\mu {\tau _\mathrm {h}} $ final states), the other ${\mathrm{t} \mathrm{\bar{t}}}$ processes lumped together, single top quark (mainly $\mathrm{t} \mathrm{W} $), DY processes (mainly the $\tau _{\ell} {\tau _\mathrm {h}} $ decay), W+jets, dibosons and multijet. The ratio of the data to the total SM prediction is shown in the lower panel. The vertical bars on the data indicate the statistical uncertainties, the hatched band indicates the systematic uncertainties and the statistical uncertainties of all simulated samples. |
png pdf |
Figure 3-c:
The pre-fit transverse mass distributions between lepton and ${{p_{\mathrm {T}}} ^\text {miss}}$, $M_{\mathrm {T}}$, in the signal-like (top) and background-like (bottom) event categories for the $\mathrm{e} {\tau _\mathrm {h}} $ (left) and $\mu {\tau _\mathrm {h}} $ (right) final states. Distributions obtained from data (full circle) are compared with simulation (shaded area). The last bin includes the overflow of the $M_{\mathrm {T}}$ distribution. The simulated contributions are normalized to the SM predicted values. The main processes are shown: the signal ($e {\tau _\mathrm {h}} $ and $\mu {\tau _\mathrm {h}} $ final states), the other ${\mathrm{t} \mathrm{\bar{t}}}$ processes lumped together, single top quark (mainly $\mathrm{t} \mathrm{W} $), DY processes (mainly the $\tau _{\ell} {\tau _\mathrm {h}} $ decay), W+jets, dibosons and multijet. The ratio of the data to the total SM prediction is shown in the lower panel. The vertical bars on the data indicate the statistical uncertainties, the hatched band indicates the systematic uncertainties and the statistical uncertainties of all simulated samples. |
png pdf |
Figure 3-d:
The pre-fit transverse mass distributions between lepton and ${{p_{\mathrm {T}}} ^\text {miss}}$, $M_{\mathrm {T}}$, in the signal-like (top) and background-like (bottom) event categories for the $\mathrm{e} {\tau _\mathrm {h}} $ (left) and $\mu {\tau _\mathrm {h}} $ (right) final states. Distributions obtained from data (full circle) are compared with simulation (shaded area). The last bin includes the overflow of the $M_{\mathrm {T}}$ distribution. The simulated contributions are normalized to the SM predicted values. The main processes are shown: the signal ($e {\tau _\mathrm {h}} $ and $\mu {\tau _\mathrm {h}} $ final states), the other ${\mathrm{t} \mathrm{\bar{t}}}$ processes lumped together, single top quark (mainly $\mathrm{t} \mathrm{W} $), DY processes (mainly the $\tau _{\ell} {\tau _\mathrm {h}} $ decay), W+jets, dibosons and multijet. The ratio of the data to the total SM prediction is shown in the lower panel. The vertical bars on the data indicate the statistical uncertainties, the hatched band indicates the systematic uncertainties and the statistical uncertainties of all simulated samples. |
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Figure 4:
The observed and expected variations of the likelihood as a function of the cross section $\sigma _{{\mathrm{t} \mathrm{\bar{t}}}}$. |
| Tables | |
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Table 1:
Expected event yields in the $\mathrm{e} {\tau _\mathrm {h}} $ and $\mu {\tau _\mathrm {h}} $ final states for signal and background processes for an integrated luminosity of 35.9 fb$^{-1}$. The expected pre-fit contributions of all processes are separated in the background-like and signal-like event categories. The statistical uncertainties of the modeling are shown for the processes estimated from the simulation. The uncertainty in the multijet contributions includes the statistical uncertainty of the data and the statistical uncertainty of the simulation of the other processes. |
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Table 2:
Systematic uncertainties determined from the fit to the observed data in the $\mathrm{e} {\tau _\mathrm {h}} $ and $\mu {\tau _\mathrm {h}} $ final states, and their combinations. Uncertainties are grouped by their origin: experimental, theoretical, and extrapolation. The uncertainties of the measurement in the dilepton final state [7] used in the partial width ratio estimate are also quoted (column "dileptons"), where the asymmetric extrapolation uncertainties are added in quadrature. Since both measurements are performed in the same data-taking period with the same reconstruction algorithms, some uncertainties are correlated as indicated in the rightmost column. |
| Summary |
| A measurement of the $\mathrm{t\bar{t}}$ production cross section in the $\tau$ dilepton channel $\mathrm{t\bar{t}}\rightarrow (\ell \nu_{\ell}) ({\tau_\mathrm{h}} \nu_{\tau}) \mathrm{b\bar{b}}$, ($\ell = $ e, $\mu$) is performed using a data sample with an integrated luminosity of 35.9 fb$^{-1}$ in proton-proton collisions at $\sqrt{s} = $ 13 TeV. Events are selected by requiring the presence of one electron or one muon, at least three jets, of which at least one is b-tagged and one is identified as a hadronically decaying $\tau$ lepton, ${\tau_\mathrm{h}}$. The largest background contribution comes from $\mathrm{t\bar{t}}$ lepton+jet events where one jet is misidentified as the ${\tau_\mathrm{h}}$. The background is constrained in a fit to the distribution of the transverse mass between lepton and missing transverse momentum, in two event categories, constructed according to the kinematic properties of the jets in the $\mathrm{t\bar{t}}$ lepton+jets final state. In the fit, the signal enters as a free parameter without constraining the kinematic properties of the $\tau$ lepton. This is the first measurement of the $\mathrm{t\bar{t}}$ production cross section in proton-proton collisions at $\sqrt{s} = $ 13 TeV that explicitly includes $\tau$ leptons, and it improves the relative precision with respect to the 7 and 8 TeV results [5,6]. The measured cross section is $\sigma_{\mathrm{t\bar{t}}}(\ell{\tau_\mathrm{h}}) = $ 781 $\pm$ 7 (stat) $\pm$ 62 (syst) $\pm$ 20 (lumi) pb for $m_{\mathrm{t}} = $ 172.5 GeV, in agreement with SM expectations. The measurement of the ratio of the cross sections in the $\ell\tau$ final state divided by the dilepton cross section yields a value $R_{\ell{\tau_\mathrm{h}}/\ell\ell}=$ 0.973 $\pm$ 0.009 (stat) $\pm$ 0.066 (syst), consistent with lepton universality. The ratio of the partial to the total width $\Gamma(\mathrm{t}\rightarrow\tau\nu_{\tau}\mathrm{b})/\Gamma_{\rm total}=$ 0.1050 $\pm$ 0.0009 (stat) $\pm$ 0.0071 (syst) is measured with respect to the $\mathrm{t\bar{t}}$ inclusive cross section in the dilepton final state [7]. |
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