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| CMS-TOP-18-007 ; CERN-EP-2021-143 | ||
| Search for CP violating top quark couplings in pp collisions at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| 16 May 2022 | ||
| JHEP 07 (2023) 023 | ||
| Abstract: Results are presented from a search for CP violation in top quark pair production, using proton-proton collisions at a center-of-mass energy of 13 TeV. The data used for this analysis consist of final states with two charged leptons collected by the CMS experiment, and correspond to an integrated luminosity of 35.9 fb$^{-1}$. The search uses two observables, ${\mathcal{O}_{1}} $ and ${\mathcal{O}_{3}} $, which are Lorentz scalars. The observable ${\mathcal{O}_{1}} $ is constructed from the four-momenta of the charged leptons and the reconstructed top quarks, while ${\mathcal{O}_{3}} $ consists of the four-momenta of the charged leptons and the b quarks originating from the top quarks. Asymmetries in these observables are sensitive to CP violation, and their measurement is used to determine the chromoelectric dipole moment of the top quark. The results are consistent with the expectation from the standard model. | ||
| Links: e-print arXiv:2205.07434 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
The comparisons of the predictions and observed data in the kinematic distributions of the ${p_{\mathrm {T}}}$ of the leading lepton (upper left), subleading lepton (upper right), leading jet (lower left), and subleading jet (lower right) in the ${\mathrm{e^{\pm}} {\mu ^\mp}}$ channels. The vertical bars on the markers of the observed data represent the statistical uncertainties. The shaded band in the predicted distributions includes statistical and systematic uncertainties. The last bin in each plot includes overflow events. The ratio of the data to the predictions from simulation is presented in the lower panel of each figure. |
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Figure 1-a:
The comparisons of the predictions and observed data in the kinematic distributions of the ${p_{\mathrm {T}}}$ of the leading lepton in the ${\mathrm{e^{\pm}} {\mu ^\mp}}$ channels. The vertical bars on the markers of the observed data represent the statistical uncertainties. The shaded band in the predicted distributions includes statistical and systematic uncertainties. The last bin includes overflow events. The ratio of the data to the predictions from simulation is presented in the lower panel. |
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Figure 1-b:
The comparisons of the predictions and observed data in the kinematic distributions of the ${p_{\mathrm {T}}}$ of the subleading lepton in the ${\mathrm{e^{\pm}} {\mu ^\mp}}$ channels. The vertical bars on the markers of the observed data represent the statistical uncertainties. The shaded band in the predicted distributions includes statistical and systematic uncertainties. The last bin includes overflow events. The ratio of the data to the predictions from simulation is presented in the lower panel. |
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Figure 1-c:
The comparisons of the predictions and observed data in the kinematic distributions of the ${p_{\mathrm {T}}}$ of the leading jet in the ${\mathrm{e^{\pm}} {\mu ^\mp}}$ channels. The vertical bars on the markers of the observed data represent the statistical uncertainties. The shaded band in the predicted distributions includes statistical and systematic uncertainties. The last bin includes overflow events. The ratio of the data to the predictions from simulation is presented in the lower panel. |
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Figure 1-d:
The comparisons of the predictions and observed data in the kinematic distributions of the ${p_{\mathrm {T}}}$ of the subleading jet in the ${\mathrm{e^{\pm}} {\mu ^\mp}}$ channels. The vertical bars on the markers of the observed data represent the statistical uncertainties. The shaded band in the predicted distributions includes statistical and systematic uncertainties. The last bin includes overflow events. The ratio of the data to the predictions from simulation is presented in the lower panel. |
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Figure 2:
The comparisons of the predictions and observed data in the ${p_{\mathrm {T}}}$ distributions in the top quark (left) and antiquark (right) in the ${\mathrm{e^{+}} \mathrm{e^{-}}}$ (upper), ${\mathrm{e^{\pm}} {\mu ^\mp}}$ (middle) and ${\mu^{+} \mu^{-}}$ (lower) channels. The vertical bars on the markers of the observed data represent the statistical uncertainties. The shaded band in the predicted distributions includes statistical and systematic uncertainties. The last bin in each plot includes overflow events. The ratio of the data to the predictions from simulation is presented in the lower panel of each figure. |
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Figure 2-a:
The comparisons of the predictions and observed data in the ${p_{\mathrm {T}}}$ distributions in the top quark in the ${\mathrm{e^{+}} \mathrm{e^{-}}}$ channel. The vertical bars on the markers of the observed data represent the statistical uncertainties. The shaded band in the predicted distributions includes statistical and systematic uncertainties. The last bin includes overflow events. The ratio of the data to the predictions from simulation is presented in the lower panel. |
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Figure 2-b:
The comparisons of the predictions and observed data in the ${p_{\mathrm {T}}}$ distributions in the top antiquark in the ${\mathrm{e^{+}} \mathrm{e^{-}}}$ channel. The vertical bars on the markers of the observed data represent the statistical uncertainties. The shaded band in the predicted distributions includes statistical and systematic uncertainties. The last bin includes overflow events. The ratio of the data to the predictions from simulation is presented in the lower panel. |
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Figure 2-c:
The comparisons of the predictions and observed data in the ${p_{\mathrm {T}}}$ distributions in the top quark in the ${\mathrm{e^{\pm}} {\mu ^\mp}}$ channel. The vertical bars on the markers of the observed data represent the statistical uncertainties. The shaded band in the predicted distributions includes statistical and systematic uncertainties. The last bin includes overflow events. The ratio of the data to the predictions from simulation is presented in the lower panel. |
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Figure 2-d:
The comparisons of the predictions and observed data in the ${p_{\mathrm {T}}}$ distributions in the top antiquark in the ${\mathrm{e^{\pm}} {\mu ^\mp}}$ channel. The vertical bars on the markers of the observed data represent the statistical uncertainties. The shaded band in the predicted distributions includes statistical and systematic uncertainties. The last bin includes overflow events. The ratio of the data to the predictions from simulation is presented in the lower panel. |
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Figure 2-e:
The comparisons of the predictions and observed data in the ${p_{\mathrm {T}}}$ distributions in the top quark in the ${\mu^{+} \mu^{-}}$ channel. The vertical bars on the markers of the observed data represent the statistical uncertainties. The shaded band in the predicted distributions includes statistical and systematic uncertainties. The last bin includes overflow events. The ratio of the data to the predictions from simulation is presented in the lower panel. |
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Figure 2-f:
The comparisons of the predictions and observed data in the ${p_{\mathrm {T}}}$ distributions in the top antiquark in the ${\mu^{+} \mu^{-}}$ channel. The vertical bars on the markers of the observed data represent the statistical uncertainties. The shaded band in the predicted distributions includes statistical and systematic uncertainties. The last bin includes overflow events. The ratio of the data to the predictions from simulation is presented in the lower panel. |
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Figure 3:
The comparisons of the predictions and observed data in ${\mathcal {O}_{1}}$ in the ${\mathrm{e^{+}} \mathrm{e^{-}}}$ (upper left), ${\mathrm{e^{\pm}} {\mu ^\mp}}$ (upper right), and ${\mu^{+} \mu^{-}}$ (lower) channel. The vertical bars on the markers of the observed data represent the statistical uncertainties. The shaded band in the predicted distributions includes statistical and systematic uncertainties. The first and last bins in each plot include underflow and overflow events, respectively. The ratio of the data to the predictions from simulation is presented in the lower panel of each figure. The solid blue shows the ratio ${(\mathrm{Im}{({d_{\mathrm{t} G}})} =2.6)/(\mathrm{Im}{({d_{\mathrm{t} G}})} =0)}$, and the dashed red line represents the ratio ${(\mathrm{Im}{({d_{\mathrm{t} G}})} =-2.6)/(\mathrm{Im}{({d_{\mathrm{t} G}})} =0)}$, using the CEDM samples. |
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Figure 3-a:
The comparisons of the predictions and observed data in ${\mathcal {O}_{1}}$ in the ${\mathrm{e^{+}} \mathrm{e^{-}}}$ channel. The vertical bars on the markers of the observed data represent the statistical uncertainties. The shaded band in the predicted distributions includes statistical and systematic uncertainties. The first and last bins include underflow and overflow events, respectively. The ratio of the data to the predictions from simulation is presented in the lower panel. The solid blue shows the ratio ${(\mathrm{Im}{({d_{\mathrm{t} G}})} =2.6)/(\mathrm{Im}{({d_{\mathrm{t} G}})} =0)}$, and the dashed red line represents the ratio ${(\mathrm{Im}{({d_{\mathrm{t} G}})} =-2.6)/(\mathrm{Im}{({d_{\mathrm{t} G}})} =0)}$, using the CEDM samples. |
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Figure 3-b:
The comparisons of the predictions and observed data in ${\mathcal {O}_{1}}$ in the ${\mathrm{e^{\pm}} {\mu ^\mp}}$ channel. The vertical bars on the markers of the observed data represent the statistical uncertainties. The shaded band in the predicted distributions includes statistical and systematic uncertainties. The first and last bins include underflow and overflow events, respectively. The ratio of the data to the predictions from simulation is presented in the lower panel. The solid blue shows the ratio ${(\mathrm{Im}{({d_{\mathrm{t} G}})} =2.6)/(\mathrm{Im}{({d_{\mathrm{t} G}})} =0)}$, and the dashed red line represents the ratio ${(\mathrm{Im}{({d_{\mathrm{t} G}})} =-2.6)/(\mathrm{Im}{({d_{\mathrm{t} G}})} =0)}$, using the CEDM samples. |
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Figure 3-c:
The comparisons of the predictions and observed data in ${\mathcal {O}_{1}}$ in the ${\mu^{+} \mu^{-}}$ channel. The vertical bars on the markers of the observed data represent the statistical uncertainties. The shaded band in the predicted distributions includes statistical and systematic uncertainties. The first and last bins include underflow and overflow events, respectively. The ratio of the data to the predictions from simulation is presented in the lower panel. The solid blue shows the ratio ${(\mathrm{Im}{({d_{\mathrm{t} G}})} =2.6)/(\mathrm{Im}{({d_{\mathrm{t} G}})} =0)}$, and the dashed red line represents the ratio ${(\mathrm{Im}{({d_{\mathrm{t} G}})} =-2.6)/(\mathrm{Im}{({d_{\mathrm{t} G}})} =0)}$, using the CEDM samples. |
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Figure 4:
The comparisons of the predictions and observed data in ${\mathcal {O}_{3}}$ in the ${\mathrm{e^{+}} \mathrm{e^{-}}}$ (upper left), ${\mathrm{e^{\pm}} {\mu ^\mp}}$ (upper right), and ${\mu^{+} \mu^{-}}$ (lower) channel. The vertical bars on the markers of the observed data represent the statistical uncertainties. The shaded band in the predicted distributions includes statistical and systematic uncertainties. The ratio of the data to the predictions from simulation is presented in the lower panel of each figure. The first and last bins in each plot includes underflow and overflow events, respectively. The solid blue line shows the ratio ${(\mathrm{Im}{({d_{\mathrm{t} G}})} =2.6)/(\mathrm{Im}{({d_{\mathrm{t} G}})} =0)}$, and the dashed red line represents the ratio ${(\mathrm{Im}{({d_{\mathrm{t} G}})} =-2.6)/(\mathrm{Im}{({d_{\mathrm{t} G}})} =0)}$, using the CEDM samples. |
png pdf |
Figure 4-a:
The comparisons of the predictions and observed data in ${\mathcal {O}_{3}}$ in the ${\mathrm{e^{+}} \mathrm{e^{-}}}$ channel. The vertical bars on the markers of the observed data represent the statistical uncertainties. The shaded band in the predicted distributions includes statistical and systematic uncertainties. The ratio of the data to the predictions from simulation is presented in the lower panel. The first and last bins include underflow and overflow events, respectively. The solid blue line shows the ratio ${(\mathrm{Im}{({d_{\mathrm{t} G}})} =2.6)/(\mathrm{Im}{({d_{\mathrm{t} G}})} =0)}$, and the dashed red line represents the ratio ${(\mathrm{Im}{({d_{\mathrm{t} G}})} =-2.6)/(\mathrm{Im}{({d_{\mathrm{t} G}})} =0)}$, using the CEDM samples. |
png pdf |
Figure 4-b:
The comparisons of the predictions and observed data in ${\mathcal {O}_{3}}$ in the ${\mathrm{e^{\pm}} {\mu ^\mp}}$ channel. The vertical bars on the markers of the observed data represent the statistical uncertainties. The shaded band in the predicted distributions includes statistical and systematic uncertainties. The ratio of the data to the predictions from simulation is presented in the lower panel. The first and last bins include underflow and overflow events, respectively. The solid blue line shows the ratio ${(\mathrm{Im}{({d_{\mathrm{t} G}})} =2.6)/(\mathrm{Im}{({d_{\mathrm{t} G}})} =0)}$, and the dashed red line represents the ratio ${(\mathrm{Im}{({d_{\mathrm{t} G}})} =-2.6)/(\mathrm{Im}{({d_{\mathrm{t} G}})} =0)}$, using the CEDM samples. |
png pdf |
Figure 4-c:
The comparisons of the predictions and observed data in ${\mathcal {O}_{3}}$ in the ${\mu^{+} \mu^{-}}$ channel. The vertical bars on the markers of the observed data represent the statistical uncertainties. The shaded band in the predicted distributions includes statistical and systematic uncertainties. The ratio of the data to the predictions from simulation is presented in the lower panel. The first and last bins include underflow and overflow events, respectively. The solid blue line shows the ratio ${(\mathrm{Im}{({d_{\mathrm{t} G}})} =2.6)/(\mathrm{Im}{({d_{\mathrm{t} G}})} =0)}$, and the dashed red line represents the ratio ${(\mathrm{Im}{({d_{\mathrm{t} G}})} =-2.6)/(\mathrm{Im}{({d_{\mathrm{t} G}})} =0)}$, using the CEDM samples. |
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Figure 5:
Asymmetries as a function of $\mathrm{Im}{({d_{\mathrm{t} G}})}$ for ${\mathcal {O}_{1}}$ (left) and ${\mathcal {O}_{3}}$ (right), for the combined dilepton channels. The inner and outer bands correspond to the uncertainties at the 68 and 95% confidence levels, respectively, of the linear fits. The square markers are the asymmetries measured using simulated samples corresponding to the different $\mathrm{Im}{({d_{\mathrm{t} G}})}$ values. The horizontal line indicates the measured asymmetry, and the shaded region reflects the total statistical and systematic uncertainty. |
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Figure 5-a:
Asymmetries as a function of $\mathrm{Im}{({d_{\mathrm{t} G}})}$ for ${\mathcal {O}_{3}}$, for the combined dilepton channels. The inner and outer bands correspond to the uncertainties at the 68 and 95% confidence levels, respectively, of the linear fits. The square markers are the asymmetries measured using simulated samples corresponding to the different $\mathrm{Im}{({d_{\mathrm{t} G}})}$ values. The horizontal line indicates the measured asymmetry, and the shaded region reflects the total statistical and systematic uncertainty. |
png pdf |
Figure 5-b:
Asymmetries as a function of $\mathrm{Im}{({d_{\mathrm{t} G}})}$ for ${\mathcal {O}_{1}}$ (left) and ${\mathcal {O}_{3}}$ (right), for the combined dilepton channels. The inner and outer bands correspond to the uncertainties at the 68 and 95% confidence levels, respectively, of the linear fits. The square markers are the asymmetries measured using simulated samples corresponding to the different $\mathrm{Im}{({d_{\mathrm{t} G}})}$ values. The horizontal line indicates the measured asymmetry, and the shaded region reflects the total statistical and systematic uncertainty. |
| Tables | |
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Table 1:
Simulated event yields with their statistical uncertainties for the three dilepton channels, after implementing event selection criteria, and normalized as described in the text. Observed selected events are also shown. |
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Table 2:
Measured asymmetries of ${\mathcal {O}_{1}}$ and ${\mathcal {O}_{3}}$ with statistical uncertainties. |
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Table 3:
Systematic uncertainties in the measured asymmetries of ${\mathcal {O}_{1}}$ and ${\mathcal {O}_{3}}$, for the individual and combined channels. |
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Table 4:
The measured dimensionless CEDM $\mathrm{Im}{({d_{\mathrm{t} G}})}$, extracted using the asymmetries in ${\mathcal {O}_{1}}$ and ${\mathcal {O}_{3}}$, with their uncertainties. |
| Summary |
| Violations of CP symmetry are studied in top quark pair production in the dilepton final state. The analysis is based on proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the CMS experiment and corresponding to an integrated luminosity of 35.9 fb$^{-1}$. The analysis uses two observables, ${\mathcal{O}_{1}} $ and ${\mathcal{O}_{3}} $, which are related to the Levi-Civita tensor contracted with the four-momenta of the leptons, the jets originating from the b quarks, and the top quarks. Asymmetries are measured in these observables and converted to measurements of the chromoelectric dipole moment (CEDM) of the top quark, represented by the dimensionless CEDM $\mathrm{Im}{({d_{\mathrm{t} G}} )} $. In the SM prediction the size of CP violation and the CEDM is negligible. The measured $\mathrm{Im}{({d_{\mathrm{t} G}} )} $ based on the asymmetries of the ${\mathcal{O}_{1}} $ and ${\mathcal{O}_{3}} $ observables in the combined dilepton channels are 0.10 $\pm$ 0.12 (stat) $\pm$ 0.12 (syst), and 0.00 $\pm$ 0.13 (stat) $\pm$ 0.10 (syst), respectively. These results are consistent with the expectation of the standard model (SM), since in the SM prediction, the size of CP violation and the CEDM ($\mathrm{Im}{({d_{\mathrm{t} G}} )} $) is negligible. In this analysis, the extracted CEDMs are compared with the CEDM measured in the $\mathrm{t\bar{t}}$ spin correlation analysis [62], and the sensitivity is found to be similar. |
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