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| CMS-PAS-TOP-19-009 | ||
| Measurement of the top quark mass in events with a single reconstructed top quark at $\sqrt{s}=$ 13 TeV | ||
| CMS Collaboration | ||
| March 2021 | ||
| Abstract: A measurement of the top quark mass is performed in a sample enriched with single top quark events produced in the $t$ channel using 35.9 fb$^{-1}$ of proton-proton collision data recorded at $\sqrt{s} =$ 13 TeV by the CMS experiment in 2016. Candidate events are selected by requiring an isolated energetic lepton (muon or electron) and exactly two jets. One of the jets is identified to originate from a bottom quark, whereas the other stems from the hadronization of a light-flavor quark. Multivariate discriminators are designed to separate signal from backgrounds, and the thresholds on the discriminator outputs are optimized to ensure an event sample with high signal purity. The mass of the top quark is found to be 172.13$^{+0.76}_{-0.77}$ GeV, reaching a sub-GeV precision for the first time in this particular phase space. The masses of top quark and antiquark are also measured separately based on the charge of the lepton in the final state, from which the mass ratio and difference are determined to be 0.995$^{+0.005}_{-0.006}$ and 0.83$^{+0.77}_{-1.01}$ GeV, respectively. | ||
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Links:
CDS record (PDF) ;
inSPIRE record ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, Submitted to JHEP. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1-a:
Feynman diagrams of $t$-channel single top quark production at LO corresponding to four- (left) and five-flavor (right) schemes. |
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Figure 1-b:
Feynman diagrams of $t$-channel single top quark production at LO corresponding to four- (left) and five-flavor (right) schemes. |
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Figure 2-a:
Event yield corresponding to positively and negatively charged muons (left) and electrons (right) in the final states obtained from simulated signal and background processes as well as in data in the 2J1T event category. |
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Figure 2-b:
Event yield corresponding to positively and negatively charged muons (left) and electrons (right) in the final states obtained from simulated signal and background processes as well as in data in the 2J1T event category. |
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Figure 3-a:
Postfit distributions of ${m_{\mathrm {T}}^{\mathrm {W}}}$ for the muon (left) and electron (right) final state in the 2J0T (top) and 2J1T (bottom) event categories. The bands represent the postfit uncertainty on the ${m_{\mathrm {T}}^{\mathrm {W}}}$ distribution predicted by the fit. |
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Figure 3-b:
Postfit distributions of ${m_{\mathrm {T}}^{\mathrm {W}}}$ for the muon (left) and electron (right) final state in the 2J0T (top) and 2J1T (bottom) event categories. The bands represent the postfit uncertainty on the ${m_{\mathrm {T}}^{\mathrm {W}}}$ distribution predicted by the fit. |
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Figure 3-c:
Postfit distributions of ${m_{\mathrm {T}}^{\mathrm {W}}}$ for the muon (left) and electron (right) final state in the 2J0T (top) and 2J1T (bottom) event categories. The bands represent the postfit uncertainty on the ${m_{\mathrm {T}}^{\mathrm {W}}}$ distribution predicted by the fit. |
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Figure 3-d:
Postfit distributions of ${m_{\mathrm {T}}^{\mathrm {W}}}$ for the muon (left) and electron (right) final state in the 2J0T (top) and 2J1T (bottom) event categories. The bands represent the postfit uncertainty on the ${m_{\mathrm {T}}^{\mathrm {W}}}$ distribution predicted by the fit. |
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Figure 4-a:
Data-MC comparisons of $\Delta \mathrm {R}_{bj^{\prime}}$ (top), light (untagged) jet $|\eta |$ (middle) and BDT response (bottom) in the 2J1T category for the muon (left) and electron (right) final state. The bands indicate the prefit statistical and systematic uncertainties added in quadrature. For the $\Delta \mathrm {R}_{bj^{\prime}}$ distributions in the top row, the last bins contain also entries with larger values. |
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Figure 4-b:
Data-MC comparisons of $\Delta \mathrm {R}_{bj^{\prime}}$ (top), light (untagged) jet $|\eta |$ (middle) and BDT response (bottom) in the 2J1T category for the muon (left) and electron (right) final state. The bands indicate the prefit statistical and systematic uncertainties added in quadrature. For the $\Delta \mathrm {R}_{bj^{\prime}}$ distributions in the top row, the last bins contain also entries with larger values. |
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Figure 4-c:
Data-MC comparisons of $\Delta \mathrm {R}_{bj^{\prime}}$ (top), light (untagged) jet $|\eta |$ (middle) and BDT response (bottom) in the 2J1T category for the muon (left) and electron (right) final state. The bands indicate the prefit statistical and systematic uncertainties added in quadrature. For the $\Delta \mathrm {R}_{bj^{\prime}}$ distributions in the top row, the last bins contain also entries with larger values. |
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Figure 4-d:
Data-MC comparisons of $\Delta \mathrm {R}_{bj^{\prime}}$ (top), light (untagged) jet $|\eta |$ (middle) and BDT response (bottom) in the 2J1T category for the muon (left) and electron (right) final state. The bands indicate the prefit statistical and systematic uncertainties added in quadrature. For the $\Delta \mathrm {R}_{bj^{\prime}}$ distributions in the top row, the last bins contain also entries with larger values. |
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Figure 4-e:
Data-MC comparisons of $\Delta \mathrm {R}_{bj^{\prime}}$ (top), light (untagged) jet $|\eta |$ (middle) and BDT response (bottom) in the 2J1T category for the muon (left) and electron (right) final state. The bands indicate the prefit statistical and systematic uncertainties added in quadrature. For the $\Delta \mathrm {R}_{bj^{\prime}}$ distributions in the top row, the last bins contain also entries with larger values. |
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Figure 4-f:
Data-MC comparisons of $\Delta \mathrm {R}_{bj^{\prime}}$ (top), light (untagged) jet $|\eta |$ (middle) and BDT response (bottom) in the 2J1T category for the muon (left) and electron (right) final state. The bands indicate the prefit statistical and systematic uncertainties added in quadrature. For the $\Delta \mathrm {R}_{bj^{\prime}}$ distributions in the top row, the last bins contain also entries with larger values. |
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Figure 5-a:
In the top row, the combined performance of the BDTs in the muon and electron final states is shown via the ROC curve (left) and a study of the signal and background efficiencies together with signal purity with different selection thresholds applied on the BDT responses (right). The arrows on the plots indicate the region of better separation (left) and final optimized selection criteria (right), respectively. The black line on the left plot corresponds to no separation between signal and background. The ROC integral is found to be about 16%. In the bottom row, a comparison of the reconstructed ${m_{\mathrm {t}}}$ templates from simulated signal events is shown on the left in the 2J1T category for different selection thresholds on the BDT responses along with their ratio relative to the case where no selection (red) is applied. The grey band represents the prefit rate uncertainty about the red curve. The optimization study is presented on the right where the combined uncertainty due to statistical and profiled systematic sources along with the uncertainty due to offset correction in the measured mass for the lepton charge inclusive case in the 2J1T category are evaluated with different selection thresholds on the BDT responses. These uncertainties are evaluated by means of a maximum likelihood fit discussed in Section 6 based on pseudoexperiments derived from simulated events. |
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Figure 5-b:
In the top row, the combined performance of the BDTs in the muon and electron final states is shown via the ROC curve (left) and a study of the signal and background efficiencies together with signal purity with different selection thresholds applied on the BDT responses (right). The arrows on the plots indicate the region of better separation (left) and final optimized selection criteria (right), respectively. The black line on the left plot corresponds to no separation between signal and background. The ROC integral is found to be about 16%. In the bottom row, a comparison of the reconstructed ${m_{\mathrm {t}}}$ templates from simulated signal events is shown on the left in the 2J1T category for different selection thresholds on the BDT responses along with their ratio relative to the case where no selection (red) is applied. The grey band represents the prefit rate uncertainty about the red curve. The optimization study is presented on the right where the combined uncertainty due to statistical and profiled systematic sources along with the uncertainty due to offset correction in the measured mass for the lepton charge inclusive case in the 2J1T category are evaluated with different selection thresholds on the BDT responses. These uncertainties are evaluated by means of a maximum likelihood fit discussed in Section 6 based on pseudoexperiments derived from simulated events. |
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Figure 5-c:
In the top row, the combined performance of the BDTs in the muon and electron final states is shown via the ROC curve (left) and a study of the signal and background efficiencies together with signal purity with different selection thresholds applied on the BDT responses (right). The arrows on the plots indicate the region of better separation (left) and final optimized selection criteria (right), respectively. The black line on the left plot corresponds to no separation between signal and background. The ROC integral is found to be about 16%. In the bottom row, a comparison of the reconstructed ${m_{\mathrm {t}}}$ templates from simulated signal events is shown on the left in the 2J1T category for different selection thresholds on the BDT responses along with their ratio relative to the case where no selection (red) is applied. The grey band represents the prefit rate uncertainty about the red curve. The optimization study is presented on the right where the combined uncertainty due to statistical and profiled systematic sources along with the uncertainty due to offset correction in the measured mass for the lepton charge inclusive case in the 2J1T category are evaluated with different selection thresholds on the BDT responses. These uncertainties are evaluated by means of a maximum likelihood fit discussed in Section 6 based on pseudoexperiments derived from simulated events. |
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Figure 5-d:
In the top row, the combined performance of the BDTs in the muon and electron final states is shown via the ROC curve (left) and a study of the signal and background efficiencies together with signal purity with different selection thresholds applied on the BDT responses (right). The arrows on the plots indicate the region of better separation (left) and final optimized selection criteria (right), respectively. The black line on the left plot corresponds to no separation between signal and background. The ROC integral is found to be about 16%. In the bottom row, a comparison of the reconstructed ${m_{\mathrm {t}}}$ templates from simulated signal events is shown on the left in the 2J1T category for different selection thresholds on the BDT responses along with their ratio relative to the case where no selection (red) is applied. The grey band represents the prefit rate uncertainty about the red curve. The optimization study is presented on the right where the combined uncertainty due to statistical and profiled systematic sources along with the uncertainty due to offset correction in the measured mass for the lepton charge inclusive case in the 2J1T category are evaluated with different selection thresholds on the BDT responses. These uncertainties are evaluated by means of a maximum likelihood fit discussed in Section 6 based on pseudoexperiments derived from simulated events. |
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Figure 6-a:
Data-MC comparison of the reconstructed ${m_{\mathrm {t}}}$ before (left) and after (right) applying optimized BDT selection criteria. The overflows are added to the last bin of each distribution. The bands represent prefit statistical and systematic uncertainties on the prediction added in quadrature. |
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Figure 6-b:
Data-MC comparison of the reconstructed ${m_{\mathrm {t}}}$ before (left) and after (right) applying optimized BDT selection criteria. The overflows are added to the last bin of each distribution. The bands represent prefit statistical and systematic uncertainties on the prediction added in quadrature. |
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Figure 7-a:
Postfit distribution of $y = \ln {m_{\mathrm {t}}} $ for the $\ell ^{+}$ (top), $\ell ^{-}$ (middle), and $\ell ^{\pm}$ (bottom) final states for signal and background processes compared to data in the 2J1T category. The bands represent the combined effect due to the statistical and profiled systematic uncertainty sources which is obtained from the fit. The fit is performed simultaneously in both lepton flavors by constructing a joint likelihood. The postfit signal ad background shapes for each lepton flavor are combined in this figure for comparison with data for the three different cases based on the lepton charge. |
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Figure 7-b:
Postfit distribution of $y = \ln {m_{\mathrm {t}}} $ for the $\ell ^{+}$ (top), $\ell ^{-}$ (middle), and $\ell ^{\pm}$ (bottom) final states for signal and background processes compared to data in the 2J1T category. The bands represent the combined effect due to the statistical and profiled systematic uncertainty sources which is obtained from the fit. The fit is performed simultaneously in both lepton flavors by constructing a joint likelihood. The postfit signal ad background shapes for each lepton flavor are combined in this figure for comparison with data for the three different cases based on the lepton charge. |
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Figure 7-c:
Postfit distribution of $y = \ln {m_{\mathrm {t}}} $ for the $\ell ^{+}$ (top), $\ell ^{-}$ (middle), and $\ell ^{\pm}$ (bottom) final states for signal and background processes compared to data in the 2J1T category. The bands represent the combined effect due to the statistical and profiled systematic uncertainty sources which is obtained from the fit. The fit is performed simultaneously in both lepton flavors by constructing a joint likelihood. The postfit signal ad background shapes for each lepton flavor are combined in this figure for comparison with data for the three different cases based on the lepton charge. |
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Figure 8-a:
Test of the linearity of the fit output for different values of true ${m_{\mathrm {t}}}$ (left) and resulting offset correction derived as a function of the postfit mass (right) for events in the 2J1T category for the $\ell ^{+}$ (top), $\ell ^{-}$ (middle), and $\ell ^{\pm}$ (bottom) cases. The shaded regions indicate $\pm $1 standard deviations about the central values defined by the red line. |
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Figure 8-b:
Test of the linearity of the fit output for different values of true ${m_{\mathrm {t}}}$ (left) and resulting offset correction derived as a function of the postfit mass (right) for events in the 2J1T category for the $\ell ^{+}$ (top), $\ell ^{-}$ (middle), and $\ell ^{\pm}$ (bottom) cases. The shaded regions indicate $\pm $1 standard deviations about the central values defined by the red line. |
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Figure 8-c:
Test of the linearity of the fit output for different values of true ${m_{\mathrm {t}}}$ (left) and resulting offset correction derived as a function of the postfit mass (right) for events in the 2J1T category for the $\ell ^{+}$ (top), $\ell ^{-}$ (middle), and $\ell ^{\pm}$ (bottom) cases. The shaded regions indicate $\pm $1 standard deviations about the central values defined by the red line. |
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Figure 8-d:
Test of the linearity of the fit output for different values of true ${m_{\mathrm {t}}}$ (left) and resulting offset correction derived as a function of the postfit mass (right) for events in the 2J1T category for the $\ell ^{+}$ (top), $\ell ^{-}$ (middle), and $\ell ^{\pm}$ (bottom) cases. The shaded regions indicate $\pm $1 standard deviations about the central values defined by the red line. |
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Figure 8-e:
Test of the linearity of the fit output for different values of true ${m_{\mathrm {t}}}$ (left) and resulting offset correction derived as a function of the postfit mass (right) for events in the 2J1T category for the $\ell ^{+}$ (top), $\ell ^{-}$ (middle), and $\ell ^{\pm}$ (bottom) cases. The shaded regions indicate $\pm $1 standard deviations about the central values defined by the red line. |
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Figure 8-f:
Test of the linearity of the fit output for different values of true ${m_{\mathrm {t}}}$ (left) and resulting offset correction derived as a function of the postfit mass (right) for events in the 2J1T category for the $\ell ^{+}$ (top), $\ell ^{-}$ (middle), and $\ell ^{\pm}$ (bottom) cases. The shaded regions indicate $\pm $1 standard deviations about the central values defined by the red line. |
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Figure 9:
A comparison of the measured ${m_{\mathrm {t}}}$ is shown with previous ATLAS and CMS measurements, namely, measurements performed by the CMS Collaboration in ${\mathrm{t} {}\mathrm{\bar{t}}}$ events at 13 TeV in fully hadronic [8], dilepton [12], and semileptonic [7] final states, respectively; along with the combinations of measurements carried out at 8 TeV by the ATLAS [5] and CMS [6] Collaborations. The previous CMS measurement at 8 TeV in single top events [14] is also considered in this comparison. The dashed black line indicates the central value obtained from this measurement in the $\ell ^{\pm}$ final state. The darker band shows the combined effect of statistical and profiled systematic uncertainties, whereas the lighter band is the total uncertainty about the central value. |
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Figure 10-a:
Data-MC comparison of $m_{\mathrm {bj^{\prime}}}$ (top), $\cos \theta ^{*}$ (middle) and ${m_{\mathrm {T}}^{\mathrm {W}}}$ (bottom) for the muon (left) and electron (right) final states in the 2J1T event category. The bands indicate the prefit statistical and systematic uncertainties added in quadrature. The overflow is added to the last bins of each plot. |
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Figure 10-b:
Data-MC comparison of $m_{\mathrm {bj^{\prime}}}$ (top), $\cos \theta ^{*}$ (middle) and ${m_{\mathrm {T}}^{\mathrm {W}}}$ (bottom) for the muon (left) and electron (right) final states in the 2J1T event category. The bands indicate the prefit statistical and systematic uncertainties added in quadrature. The overflow is added to the last bins of each plot. |
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Figure 10-c:
Data-MC comparison of $m_{\mathrm {bj^{\prime}}}$ (top), $\cos \theta ^{*}$ (middle) and ${m_{\mathrm {T}}^{\mathrm {W}}}$ (bottom) for the muon (left) and electron (right) final states in the 2J1T event category. The bands indicate the prefit statistical and systematic uncertainties added in quadrature. The overflow is added to the last bins of each plot. |
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Figure 10-d:
Data-MC comparison of $m_{\mathrm {bj^{\prime}}}$ (top), $\cos \theta ^{*}$ (middle) and ${m_{\mathrm {T}}^{\mathrm {W}}}$ (bottom) for the muon (left) and electron (right) final states in the 2J1T event category. The bands indicate the prefit statistical and systematic uncertainties added in quadrature. The overflow is added to the last bins of each plot. |
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Figure 10-e:
Data-MC comparison of $m_{\mathrm {bj^{\prime}}}$ (top), $\cos \theta ^{*}$ (middle) and ${m_{\mathrm {T}}^{\mathrm {W}}}$ (bottom) for the muon (left) and electron (right) final states in the 2J1T event category. The bands indicate the prefit statistical and systematic uncertainties added in quadrature. The overflow is added to the last bins of each plot. |
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Figure 10-f:
Data-MC comparison of $m_{\mathrm {bj^{\prime}}}$ (top), $\cos \theta ^{*}$ (middle) and ${m_{\mathrm {T}}^{\mathrm {W}}}$ (bottom) for the muon (left) and electron (right) final states in the 2J1T event category. The bands indicate the prefit statistical and systematic uncertainties added in quadrature. The overflow is added to the last bins of each plot. |
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Figure 11-a:
Data-MC comparisons of $| \Delta \eta _{\ell \mathrm {b}} | $ and $ {p_{\mathrm {T}}} ^{\mathrm {b}} + {p_{\mathrm {T}}} ^{\mathrm {j}^{\prime}}$ are presented in top and the middle row for muon (left) and electron (right) final states in the 2J1T event category. Th bottom row shows the data-MC comparisons of $| \eta _{\ell} | $ (left) and FW1 (right) for the muon (left) and electron (right) final states, respectively in the 2J1T event category. The bands indicate the prefit statistical and systematic uncertainties added in quadrature. The overflow is added to the last bins in the case of each plot except for the one in bottom-right. |
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Figure 11-b:
Data-MC comparisons of $| \Delta \eta _{\ell \mathrm {b}} | $ and $ {p_{\mathrm {T}}} ^{\mathrm {b}} + {p_{\mathrm {T}}} ^{\mathrm {j}^{\prime}}$ are presented in top and the middle row for muon (left) and electron (right) final states in the 2J1T event category. Th bottom row shows the data-MC comparisons of $| \eta _{\ell} | $ (left) and FW1 (right) for the muon (left) and electron (right) final states, respectively in the 2J1T event category. The bands indicate the prefit statistical and systematic uncertainties added in quadrature. The overflow is added to the last bins in the case of each plot except for the one in bottom-right. |
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Figure 11-c:
Data-MC comparisons of $| \Delta \eta _{\ell \mathrm {b}} | $ and $ {p_{\mathrm {T}}} ^{\mathrm {b}} + {p_{\mathrm {T}}} ^{\mathrm {j}^{\prime}}$ are presented in top and the middle row for muon (left) and electron (right) final states in the 2J1T event category. Th bottom row shows the data-MC comparisons of $| \eta _{\ell} | $ (left) and FW1 (right) for the muon (left) and electron (right) final states, respectively in the 2J1T event category. The bands indicate the prefit statistical and systematic uncertainties added in quadrature. The overflow is added to the last bins in the case of each plot except for the one in bottom-right. |
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Figure 11-d:
Data-MC comparisons of $| \Delta \eta _{\ell \mathrm {b}} | $ and $ {p_{\mathrm {T}}} ^{\mathrm {b}} + {p_{\mathrm {T}}} ^{\mathrm {j}^{\prime}}$ are presented in top and the middle row for muon (left) and electron (right) final states in the 2J1T event category. Th bottom row shows the data-MC comparisons of $| \eta _{\ell} | $ (left) and FW1 (right) for the muon (left) and electron (right) final states, respectively in the 2J1T event category. The bands indicate the prefit statistical and systematic uncertainties added in quadrature. The overflow is added to the last bins in the case of each plot except for the one in bottom-right. |
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Figure 11-e:
Data-MC comparisons of $| \Delta \eta _{\ell \mathrm {b}} | $ and $ {p_{\mathrm {T}}} ^{\mathrm {b}} + {p_{\mathrm {T}}} ^{\mathrm {j}^{\prime}}$ are presented in top and the middle row for muon (left) and electron (right) final states in the 2J1T event category. Th bottom row shows the data-MC comparisons of $| \eta _{\ell} | $ (left) and FW1 (right) for the muon (left) and electron (right) final states, respectively in the 2J1T event category. The bands indicate the prefit statistical and systematic uncertainties added in quadrature. The overflow is added to the last bins in the case of each plot except for the one in bottom-right. |
png pdf |
Figure 11-f:
Data-MC comparisons of $| \Delta \eta _{\ell \mathrm {b}} | $ and $ {p_{\mathrm {T}}} ^{\mathrm {b}} + {p_{\mathrm {T}}} ^{\mathrm {j}^{\prime}}$ are presented in top and the middle row for muon (left) and electron (right) final states in the 2J1T event category. Th bottom row shows the data-MC comparisons of $| \eta _{\ell} | $ (left) and FW1 (right) for the muon (left) and electron (right) final states, respectively in the 2J1T event category. The bands indicate the prefit statistical and systematic uncertainties added in quadrature. The overflow is added to the last bins in the case of each plot except for the one in bottom-right. |
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Figure 12-a:
Correlations (in %) among for the input variables to the BDT designed for the muon final state in signal (top) and background (bottom) events in the 2J1T category before (left) and after (right) application of the decorrelation method available in TMVA. |
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Figure 12-b:
Correlations (in %) among for the input variables to the BDT designed for the muon final state in signal (top) and background (bottom) events in the 2J1T category before (left) and after (right) application of the decorrelation method available in TMVA. |
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Figure 12-c:
Correlations (in %) among for the input variables to the BDT designed for the muon final state in signal (top) and background (bottom) events in the 2J1T category before (left) and after (right) application of the decorrelation method available in TMVA. |
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Figure 12-d:
Correlations (in %) among for the input variables to the BDT designed for the muon final state in signal (top) and background (bottom) events in the 2J1T category before (left) and after (right) application of the decorrelation method available in TMVA. |
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Figure 13-a:
Correlations (in %) among for the input variables to the BDT designed for the electron final state in signal (top) and background (bottom) events in the 2J1T category before (left) and after (right) application of the decorrelation method available in TMVA. |
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Figure 13-b:
Correlations (in %) among for the input variables to the BDT designed for the electron final state in signal (top) and background (bottom) events in the 2J1T category before (left) and after (right) application of the decorrelation method available in TMVA. |
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Figure 13-c:
Correlations (in %) among for the input variables to the BDT designed for the electron final state in signal (top) and background (bottom) events in the 2J1T category before (left) and after (right) application of the decorrelation method available in TMVA. |
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Figure 13-d:
Correlations (in %) among for the input variables to the BDT designed for the electron final state in signal (top) and background (bottom) events in the 2J1T category before (left) and after (right) application of the decorrelation method available in TMVA. |
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Figure 14-a:
The scan of the profile likelihood ratios as a function of the POI in the parametric model are shown on the left for the fits corresponding to $\ell ^{\pm}$ final state in the 2J1T event category with simulated events and data. The correlation (in %) among the POI and nuisance parameters are shown on the right for the fit to data corresponding to $\ell ^{\pm}$ final state in the 2J1T event category. |
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Figure 14-b:
The scan of the profile likelihood ratios as a function of the POI in the parametric model are shown on the left for the fits corresponding to $\ell ^{\pm}$ final state in the 2J1T event category with simulated events and data. The correlation (in %) among the POI and nuisance parameters are shown on the right for the fit to data corresponding to $\ell ^{\pm}$ final state in the 2J1T event category. |
| Summary |
| Events containing an isolated muon or electron and two jets, of which one is b-tagged, in the final state are used to measure the mass of top quarks and antiquarks, as well as their ratio and difference in the $t$ channel single top production. The top quark mass is measured to be 172.13$^{+0.76}_{-0.77}$ GeV from the inclusive measurement. For the very first time, a sub-GeV precision on the measured mass is achieved in this particular phase space. The masses of the top quark and antiquark are determined to be 172.62$^{+1.04}_{-0.75}$ GeV and 171.79$^{+1.44}_{-1.51}$ GeV, respectively. These quantities are used to determine the ratio of the masses of the top antiquarks to the quarks to be 0.995$^{+0.005}_{-0.006}$ along with the difference between top quark and antiquark masses to be 0.83$^{+0.77}_{-1.01}$ GeV, for the first time in events with single top quark production. The estimated mass ratio and difference agree with unity and zero, respectively, within uncertainties and are consistent with no violation of the charge conjugation-parity-time reversal invariance. The statistical uncertainty plays a minor role in the achieved precision of the measured masses, which are limited by the systematic uncertainties due to jet energy scale, color reconnection, and modeling of final state radiation in the signal process. A deeper understanding of these effects is therefore crucial not only to further improve the precisions of the measured masses; also for a deeper knowledge of their correlations in events with single top quark and antiquark production, in order to determine stringent limit for any violation of the charge conjugation-parity-time reversal invariance in this process in future. |
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