CMS-TOP-13-004 ; CERN-EP-2016-044 | ||
Measurement of the $\mathrm{ t \bar{t} }$ production cross section in the $\mathrm{ e } \mu$ channel in proton-proton collisions at $\sqrt{s} = $ 7 and 8 TeV | ||
CMS Collaboration | ||
7 March 2016 | ||
J. High Energy Phys. 08 (2016) 029 | ||
Abstract: The inclusive cross section for top quark pair production is measured in proton-proton collisions at $\sqrt{s} = $ 7 and 8 TeV, corresponding to 5.0 and 19.7 fb$^{-1}$, respectively, with the CMS experiment at the LHC. The cross sections are measured in the electron-muon channel using a binned likelihood fit to multi-differential final state distributions related to identified b quark jets and other jets in the event. The measured cross section values are 173.6 $\pm$ 2.1 (stat) $^{+\,4.5}_{-\,4.0}$ (syst) $\pm$ 3.8 (lumi) pb at $ \sqrt{s} = $ 7 TeV, and 244.9 $\pm$ 1.4 (stat) $^{+\,6.3}_{-\,5.5}$ (syst) $\pm$ 6.4 (lumi) pb at $ \sqrt{s} = $ 8 TeV, in good agreement with QCD calculations at next-to-next-to-leading-order accuracy. The ratio of the cross sections measured at 7 and 8 TeV is determined, as well as cross sections in the fiducial regions defined by the acceptance requirements on the two charged leptons in the final state. The cross section results are used to determine the top quark pole mass via the dependence of the theoretically predicted cross section on the mass, giving a best result of 173.8 $^{+1.7}_{-1.8}$ GeV. The data at $\sqrt{s}= $ 8 TeV are also used to set limits, for two neutralino mass values, on the pair production of supersymmetric partners of the top quark with masses close to the top quark mass. | ||
Links: e-print arXiv:1603.02303 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; |
Figures | |
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Figure 1:
Distributions of $ {p_{\mathrm {T}}} $ (left) and $\eta $ (right) of the leading (top) and subleading (bottom) leptons, after the $ {\mathrm{ e } \mu } $ selection, for the 7 TeV data. The last bin of the $ {p_{\mathrm {T}}} $ distributions includes the overflow events. The hatched bands correspond to the total uncertainty in the sum of the predicted yields. The ratios of data to the sum of the predicted yields are shown at the bottom of each plot. Here, an additional solid gray band represents the contribution from the statistical uncertainty in the MC simulation. The contributing systematic uncertainties are discussed in Section 7. |
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Figure 1-a:
Distribution of $ {p_{\mathrm {T}}} $ of the leading lepton, after the $ {\mathrm{ e } \mu } $ selection, for the 7 TeV data. The last bin of the $ {p_{\mathrm {T}}} $ distributions includes the overflow events. The hatched bands correspond to the total uncertainty in the sum of the predicted yields. The ratios of data to the sum of the predicted yields are shown at the bottom of each plot. Here, an additional solid gray band represents the contribution from the statistical uncertainty in the MC simulation. The contributing systematic uncertainties are discussed in Section 7. |
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Figure 1-b:
Distribution of $\eta $ of the leading lepton, after the $ {\mathrm{ e } \mu } $ selection, for the 7 TeV data. The last bin of the $ {p_{\mathrm {T}}} $ distributions includes the overflow events. The hatched bands correspond to the total uncertainty in the sum of the predicted yields. The ratios of data to the sum of the predicted yields are shown at the bottom of each plot. Here, an additional solid gray band represents the contribution from the statistical uncertainty in the MC simulation. The contributing systematic uncertainties are discussed in Section 7. |
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Figure 1-c:
Distribution of $ {p_{\mathrm {T}}} $ of the subleading lepton, after the $ {\mathrm{ e } \mu } $ selection, for the 7 TeV data. The last bin of the $ {p_{\mathrm {T}}} $ distributions includes the overflow events. The hatched bands correspond to the total uncertainty in the sum of the predicted yields. The ratios of data to the sum of the predicted yields are shown at the bottom of each plot. Here, an additional solid gray band represents the contribution from the statistical uncertainty in the MC simulation. The contributing systematic uncertainties are discussed in Section 7. |
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Figure 1-d:
Distribution of $\eta $ of the subleading lepton, after the $ {\mathrm{ e } \mu } $ selection, for the 7 TeV data. The last bin of the $ {p_{\mathrm {T}}} $ distributions includes the overflow events. The hatched bands correspond to the total uncertainty in the sum of the predicted yields. The ratios of data to the sum of the predicted yields are shown at the bottom of each plot. Here, an additional solid gray band represents the contribution from the statistical uncertainty in the MC simulation. The contributing systematic uncertainties are discussed in Section 7. |
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Figure 2:
Distributions of $ {p_{\mathrm {T}}} $ (left) and $\eta $ (right) of the leading (top) and subleading (bottom) leptons, after the $ {\mathrm{ e } \mu } $ selection, for the 8 TeV data. The last bin of the $ {p_{\mathrm {T}}} $ distributions includes the overflow events. The hatched bands correspond to the total uncertainty in the sum of the predicted yields. The ratios of data to the sum of the predicted yields are shown at the bottom of each plot. Here, an additional solid grey band represents the contribution from the statistical uncertainty in the MC simulation. The contributing systematic uncertainties are discussed in Section 7. |
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Figure 2-a:
Distribution of $ {p_{\mathrm {T}}} $ of the leading lepton, after the $ {\mathrm{ e } \mu } $ selection, for the 8 TeV data. The last bin of the $ {p_{\mathrm {T}}} $ distributions includes the overflow events. The hatched bands correspond to the total uncertainty in the sum of the predicted yields. The ratios of data to the sum of the predicted yields are shown at the bottom of each plot. Here, an additional solid grey band represents the contribution from the statistical uncertainty in the MC simulation. The contributing systematic uncertainties are discussed in Section 7. |
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Figure 2-b:
Distribution of $\eta $ of the leading lepton, after the $ {\mathrm{ e } \mu } $ selection, for the 8 TeV data. The last bin of the $ {p_{\mathrm {T}}} $ distributions includes the overflow events. The hatched bands correspond to the total uncertainty in the sum of the predicted yields. The ratios of data to the sum of the predicted yields are shown at the bottom of each plot. Here, an additional solid grey band represents the contribution from the statistical uncertainty in the MC simulation. The contributing systematic uncertainties are discussed in Section 7. |
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Figure 2-c:
Distribution of $ {p_{\mathrm {T}}} $ of the subleading lepton, after the $ {\mathrm{ e } \mu } $ selection, for the 8 TeV data. The last bin of the $ {p_{\mathrm {T}}} $ distributions includes the overflow events. The hatched bands correspond to the total uncertainty in the sum of the predicted yields. The ratios of data to the sum of the predicted yields are shown at the bottom of each plot. Here, an additional solid grey band represents the contribution from the statistical uncertainty in the MC simulation. The contributing systematic uncertainties are discussed in Section 7. |
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Figure 2-d:
Distribution of $\eta $ of the subleading lepton, after the $ {\mathrm{ e } \mu } $ selection, for the 8 TeV data. The last bin of the $ {p_{\mathrm {T}}} $ distributions includes the overflow events. The hatched bands correspond to the total uncertainty in the sum of the predicted yields. The ratios of data to the sum of the predicted yields are shown at the bottom of each plot. Here, an additional solid grey band represents the contribution from the statistical uncertainty in the MC simulation. The contributing systematic uncertainties are discussed in Section 7. |
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Figure 3:
Number of b-tagged jets after the $ {\mathrm{ e } \mu } $ selection for 7 TeV (left) and 8 TeV (right). The hatched bands correspond to the total uncertainty in the sum of the predicted yields. The ratios of data to the sum of the predicted yields are shown at the bottom of each plot. Here, an additional solid grey band represents the contribution from the statistical uncertainty in the MC simulation. The contributing systematic uncertainties are discussed in Section 7. |
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Figure 3-a:
Number of b-tagged jets after the $ {\mathrm{ e } \mu } $ selection for 7 TeV. The hatched bands correspond to the total uncertainty in the sum of the predicted yields. The ratios of data to the sum of the predicted yields are shown at the bottom of each plot. Here, an additional solid grey band represents the contribution from the statistical uncertainty in the MC simulation. The contributing systematic uncertainties are discussed in Section 7. |
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Figure 3-b:
Number of b-tagged jets after the $ {\mathrm{ e } \mu } $ selection for 8 TeV (right). The hatched bands correspond to the total uncertainty in the sum of the predicted yields. The ratios of data to the sum of the predicted yields are shown at the bottom of each plot. Here, an additional solid grey band represents the contribution from the statistical uncertainty in the MC simulation. The contributing systematic uncertainties are discussed in Section 7. |
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Figure 4:
Total event yield for zero additional non-b-tagged jets (left) and $ {p_{\mathrm {T}}} $ of the non-b-tagged jet with the lowest $ {p_{\mathrm {T}}} $ in the event (right) for events with one, two, and at least three additional non-b-tagged jets, and with zero or more than two (top row), one (middle row), and two (bottom row) b-tagged jets at $ \sqrt{s} = $ 7 TeV. The last bin of the $ {p_{\mathrm {T}}} $ distributions includes the overflow events. The hatched bands correspond to the sum of statistical and systematic uncertainties in the event yield for the sum of signal and background predictions. The ratios of data to the sum of the predicted yields are shown at the bottom of each plot. Here, an additional solid grey band represents the contribution from the statistical uncertainty in the MC simulation. |
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Figure 4-a:
Total event yield for zero additional non-b-tagged jets (left) and $ {p_{\mathrm {T}}} $ of the non-b-tagged jet with the lowest $ {p_{\mathrm {T}}} $ in the event (right) for events with one, two, and at least three additional non-b-tagged jets, and with zero or more than two (top row), one (middle row), and two (bottom row) b-tagged jets at $ \sqrt{s} = $ 7 TeV. The last bin of the $ {p_{\mathrm {T}}} $ distributions includes the overflow events. The hatched bands correspond to the sum of statistical and systematic uncertainties in the event yield for the sum of signal and background predictions. The ratios of data to the sum of the predicted yields are shown at the bottom of each plot. Here, an additional solid grey band represents the contribution from the statistical uncertainty in the MC simulation. |
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Figure 4-b:
Total event yield for zero additional non-b-tagged jets (left) and $ {p_{\mathrm {T}}} $ of the non-b-tagged jet with the lowest $ {p_{\mathrm {T}}} $ in the event (right) for events with one, two, and at least three additional non-b-tagged jets, and with one b-tagged jets at $ \sqrt{s} = $ 7 TeV. The last bin of the $ {p_{\mathrm {T}}} $ distributions includes the overflow events. The hatched bands correspond to the sum of statistical and systematic uncertainties in the event yield for the sum of signal and background predictions. The ratios of data to the sum of the predicted yields are shown at the bottom of each plot. Here, an additional solid grey band represents the contribution from the statistical uncertainty in the MC simulation. |
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Figure 4-c:
Total event yield for zero additional non-b-tagged jets (left) and $ {p_{\mathrm {T}}} $ of the non-b-tagged jet with the lowest $ {p_{\mathrm {T}}} $ in the event (right) for events with one, two, and at least three additional non-b-tagged jets, and with two b-tagged jets at $ \sqrt{s} = $ 7 TeV. The last bin of the $ {p_{\mathrm {T}}} $ distributions includes the overflow events. The hatched bands correspond to the sum of statistical and systematic uncertainties in the event yield for the sum of signal and background predictions. The ratios of data to the sum of the predicted yields are shown at the bottom of each plot. Here, an additional solid grey band represents the contribution from the statistical uncertainty in the MC simulation. |
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Figure 5:
Total event yield for zero additional non-b-tagged jets (left) and $ {p_{\mathrm {T}}} $ of the additional non-b-tagged jet with the lowest $ {p_{\mathrm {T}}} $ in the event (right) for events with one, two, and at least three additional non-b-tagged jets, and with zero or more than two (top row), one (middle row), and two (bottom row) b-tagged jets at $ \sqrt{s} = $ 8 TeV. The last bin of the $ {p_{\mathrm {T}}} $ distributions includes the overflow events. The hatched bands correspond to the sum of statistical and systematic uncertainties in the event yield for the sum of signal and background predictions. The ratios of data to the sum of the predicted yields are shown at the bottom of each plot. Here, an additional solid grey band represents the contribution from the statistical uncertainty in the MC simulation. |
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Figure 5-a:
Total event yield for zero additional non-b-tagged jets (left) and $ {p_{\mathrm {T}}} $ of the additional non-b-tagged jet with the lowest $ {p_{\mathrm {T}}} $ in the event (right) for events with one, two, and at least three additional non-b-tagged jets, and with zero or more than two b-tagged jets at $ \sqrt{s} = $ 8 TeV. The last bin of the $ {p_{\mathrm {T}}} $ distributions includes the overflow events. The hatched bands correspond to the sum of statistical and systematic uncertainties in the event yield for the sum of signal and background predictions. The ratios of data to the sum of the predicted yields are shown at the bottom of each plot. Here, an additional solid grey band represents the contribution from the statistical uncertainty in the MC simulation. |
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Figure 5-b:
Total event yield for zero additional non-b-tagged jets (left) and $ {p_{\mathrm {T}}} $ of the additional non-b-tagged jet with the lowest $ {p_{\mathrm {T}}} $ in the event (right) for events with one, two, and at least three additional non-b-tagged jets, and with one b-tagged jets at $ \sqrt{s} = $ 8 TeV. The last bin of the $ {p_{\mathrm {T}}} $ distributions includes the overflow events. The hatched bands correspond to the sum of statistical and systematic uncertainties in the event yield for the sum of signal and background predictions. The ratios of data to the sum of the predicted yields are shown at the bottom of each plot. Here, an additional solid grey band represents the contribution from the statistical uncertainty in the MC simulation. |
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Figure 5-c:
Total event yield for zero additional non-b-tagged jets (left) and $ {p_{\mathrm {T}}} $ of the additional non-b-tagged jet with the lowest $ {p_{\mathrm {T}}} $ in the event (right) for events with one, two, and at least three additional non-b-tagged jets, and with two b-tagged jets at $ \sqrt{s} = $ 8 TeV. The last bin of the $ {p_{\mathrm {T}}} $ distributions includes the overflow events. The hatched bands correspond to the sum of statistical and systematic uncertainties in the event yield for the sum of signal and background predictions. The ratios of data to the sum of the predicted yields are shown at the bottom of each plot. Here, an additional solid grey band represents the contribution from the statistical uncertainty in the MC simulation. |
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Figure 6:
Fitted total event yield for zero additional non-b-tagged jets (left) and $ {p_{\mathrm {T}}} $ of the non-b-tagged jet with the lowest $ {p_{\mathrm {T}}} $ in the event (right) for events with one, two, and at least three additional non-b-tagged jets, and with zero or more than two (top row), one (middle row), and two (bottom row) b-tagged jets at $ \sqrt{s} = $ 7 TeV. The last bin of the $ {p_{\mathrm {T}}} $ distributions includes the overflow events. The hatched bands correspond to the sum of statistical and systematic uncertainties in the event yield for the sum of signal and background predictions after the fit, and include all correlations. The ratios of data to the sum of the predicted yields are shown at the bottom of each plot. Here, an additional solid grey band represents the contribution from the statistical uncertainty in the MC simulation. |
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Figure 6-a:
Fitted total event yield for zero additional non-b-tagged jets (left) and $ {p_{\mathrm {T}}} $ of the non-b-tagged jet with the lowest $ {p_{\mathrm {T}}} $ in the event (right) for events with one, two, and at least three additional non-b-tagged jets, and with zero or more than two b-tagged jets at $ \sqrt{s} = $ 7 TeV. The last bin of the $ {p_{\mathrm {T}}} $ distributions includes the overflow events. The hatched bands correspond to the sum of statistical and systematic uncertainties in the event yield for the sum of signal and background predictions after the fit, and include all correlations. The ratios of data to the sum of the predicted yields are shown at the bottom of each plot. Here, an additional solid grey band represents the contribution from the statistical uncertainty in the MC simulation. |
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Figure 6-b:
Fitted total event yield for zero additional non-b-tagged jets (left) and $ {p_{\mathrm {T}}} $ of the non-b-tagged jet with the lowest $ {p_{\mathrm {T}}} $ in the event (right) for events with one, two, and at least three additional non-b-tagged jets, and with one b-tagged jets at $ \sqrt{s} = $ 7 TeV. The last bin of the $ {p_{\mathrm {T}}} $ distributions includes the overflow events. The hatched bands correspond to the sum of statistical and systematic uncertainties in the event yield for the sum of signal and background predictions after the fit, and include all correlations. The ratios of data to the sum of the predicted yields are shown at the bottom of each plot. Here, an additional solid grey band represents the contribution from the statistical uncertainty in the MC simulation. |
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Figure 6-c:
Fitted total event yield for zero additional non-b-tagged jets (left) and $ {p_{\mathrm {T}}} $ of the non-b-tagged jet with the lowest $ {p_{\mathrm {T}}} $ in the event (right) for events with one, two, and at least three additional non-b-tagged jets, and with two b-tagged jets at $ \sqrt{s} = $ 7 TeV. The last bin of the $ {p_{\mathrm {T}}} $ distributions includes the overflow events. The hatched bands correspond to the sum of statistical and systematic uncertainties in the event yield for the sum of signal and background predictions after the fit, and include all correlations. The ratios of data to the sum of the predicted yields are shown at the bottom of each plot. Here, an additional solid grey band represents the contribution from the statistical uncertainty in the MC simulation. |
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Figure 7:
Fitted total event yield for zero additional non-b-tagged jets (left) and $ {p_{\mathrm {T}}} $ of the non-b-tagged jet with the lowest $ {p_{\mathrm {T}}} $ in the event (right) for events with one, two, and at least three additional non-b-tagged jets, and with zero or more than two (top row), one (middle row), and two (bottom row) b-tagged jets at $ \sqrt{s} = $ 8 TeV. The last bin of the $ {p_{\mathrm {T}}} $ distributions includes the overflow events. The hatched bands correspond to the sum of statistical and systematic uncertainties in the event yield for the sum of signal and background predictions after the fit, and include all correlations. The ratios of data to the sum of the predicted yields are shown at the bottom of each plot. Here, an additional solid grey band represents the contribution from the statistical uncertainty in the MC simulation. |
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Figure 7-a:
Fitted total event yield for zero additional non-b-tagged jets (left) and $ {p_{\mathrm {T}}} $ of the non-b-tagged jet with the lowest $ {p_{\mathrm {T}}} $ in the event (right) for events with one, two, and at least three additional non-b-tagged jets, and with zero or more than two b-tagged jets at $ \sqrt{s} = $ 8 TeV. The last bin of the $ {p_{\mathrm {T}}} $ distributions includes the overflow events. The hatched bands correspond to the sum of statistical and systematic uncertainties in the event yield for the sum of signal and background predictions after the fit, and include all correlations. The ratios of data to the sum of the predicted yields are shown at the bottom of each plot. Here, an additional solid grey band represents the contribution from the statistical uncertainty in the MC simulation. |
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Figure 7-b:
Fitted total event yield for zero additional non-b-tagged jets (left) and $ {p_{\mathrm {T}}} $ of the non-b-tagged jet with the lowest $ {p_{\mathrm {T}}} $ in the event (right) for events with one, two, and at least three additional non-b-tagged jets, and with one b-tagged jets at $ \sqrt{s} = $ 8 TeV. The last bin of the $ {p_{\mathrm {T}}} $ distributions includes the overflow events. The hatched bands correspond to the sum of statistical and systematic uncertainties in the event yield for the sum of signal and background predictions after the fit, and include all correlations. The ratios of data to the sum of the predicted yields are shown at the bottom of each plot. Here, an additional solid grey band represents the contribution from the statistical uncertainty in the MC simulation. |
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Figure 7-c:
Fitted total event yield for zero additional non-b-tagged jets (left) and $ {p_{\mathrm {T}}} $ of the non-b-tagged jet with the lowest $ {p_{\mathrm {T}}} $ in the event (right) for events with one, two, and at least three additional non-b-tagged jets, and with two b-tagged jets at $ \sqrt{s} = $ 8 TeV. The last bin of the $ {p_{\mathrm {T}}} $ distributions includes the overflow events. The hatched bands correspond to the sum of statistical and systematic uncertainties in the event yield for the sum of signal and background predictions after the fit, and include all correlations. The ratios of data to the sum of the predicted yields are shown at the bottom of each plot. Here, an additional solid grey band represents the contribution from the statistical uncertainty in the MC simulation. |
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Figure 8:
Comparison of the b jet multiplicity distributions in the $ {\mathrm{ e } \mu } $ channel for 8 TeV between the data and simulation for events fulfilling the $ {\mathrm{ e } \mu } $ selection and the requirement of having at least two jets. The hatched bands correspond to the sum of statistical and systematic uncertainties in the event yield for the signal and background predictions. The ratios of data to the predicted yields are shown at the bottom of each plot. Here, an additional solid grey band represents the contribution from the statistical uncertainty in the MC simulation. |
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Figure 8-a:
Comparison of the b jet multiplicity distributions in the $ {\mathrm{ e } \mu } $ channel for 7 TeV between the data and simulation for events fulfilling the $ {\mathrm{ e } \mu } $ selection and the requirement of having at least two jets. The hatched bands correspond to the sum of statistical and systematic uncertainties in the event yield for the signal and background predictions. The ratios of data to the predicted yields are shown at the bottom of each plot. Here, an additional solid grey band represents the contribution from the statistical uncertainty in the MC simulation. |
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Figure 8-b:
Comparison of the b jet multiplicity distributions in the $ {\mathrm{ e } \mu } $ channel for 8 TeV between the data and simulation for events fulfilling the $ {\mathrm{ e } \mu } $ selection and the requirement of having at least two jets. The hatched bands correspond to the sum of statistical and systematic uncertainties in the event yield for the signal and background predictions. The ratios of data to the predicted yields are shown at the bottom of each plot. Here, an additional solid grey band represents the contribution from the statistical uncertainty in the MC simulation. |
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Figure 9:
Likelihood for the predicted dependence of the $ {\mathrm{ t } {}\mathrm{ \bar{t} } } $ production cross section on the top quark pole mass for 7 and 8 TeV determined with TOP++, employing the NNPDF3.0 PDF set. The measured dependences on the mass are given by the dashed lines, their 1$\sigma $-uncertainties are represented by the dotted lines. The extracted mass at each value of $\sqrt {s}$ is indicated by a black point, with its 1$\sigma $-uncertainty constructed from the continuous contour, corresponding to $-2\Delta \log(L_\text {pred} L_\text {exp}) =$ 1. |
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Figure 10:
Diagram displaying the top squark pair production at the LHC in the decay mode where each top squark decays to a top quark and a neutralino $\tilde{\chi}^0_1 $. |
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Figure 11:
Expected and observed limits at 95% CL on the signal strength (see text) as a function of the top squark mass for neutralino masses of 1 GeV (left) and 12.5 GeV (right). The widest bands show the 68% and 95% CL ranges of the expected limit. The narrowest band quantifies the impact of the theoretical uncertainty in the cross section of the SUSY signal on the observed limit. |
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Figure 11-a:
Expected and observed limits at 95% CL on the signal strength (see text) as a function of the top squark mass for neutralino masses of 1 GeV. The widest bands show the 68% and 95% CL ranges of the expected limit. The narrowest band quantifies the impact of the theoretical uncertainty in the cross section of the SUSY signal on the observed limit. |
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Figure 11-b:
Expected and observed limits at 95% CL on the signal strength (see text) as a function of the top squark mass for neutralino masses of 12.5 GeV. The widest bands show the 68% and 95% CL ranges of the expected limit. The narrowest band quantifies the impact of the theoretical uncertainty in the cross section of the SUSY signal on the observed limit. |
Tables | |
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Table 1:
Number of selected events for the event counting method for the 7 and 8 TeV data sets. The results are given for the individual sources of background, $ {\mathrm{ t } {}\mathrm{ \bar{t} } } $ signal, and data. The two uncertainties quoted correspond to the statistical and systematic components (cf. Section 7), respectively. |
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Table 2:
Assumed correlations $\rho $ between systematic uncertainties for the 7 and 8 TeV data sets. If $\rho =$ 0, the uncertainties are treated as uncorrelated between the two sets. |
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Table 3:
Illustrative summary of the individual contributions to the total uncertainty in the visible $ {\mathrm{ t } {}\mathrm{ \bar{t} } } $ cross section measurements. |
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Table 4:
Individual contributions to the systematic uncertainty in the total $ {\mathrm{ t } {}\mathrm{ \bar{t} } } $ cross section measurements. The total systematic uncertainties in the fiducial cross sections $\sigma ^{\text {vis}}_{{\mathrm{ t } {}\mathrm{ \bar{t} } } }$ are given in the row ``Total (visible)'', and those in the full phase space cross section $ {\sigma _{{\mathrm{ t } {}\mathrm{ \bar{t} } } }}$ in the row ``Total''. |
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Table 5:
Top quark pole mass at NNLO+NNLL extracted by comparing the measured $ {\mathrm{ t } {}\mathrm{ \bar{t} } } $ production cross section at 7 and 8 TeV with predictions employing different PDF sets. |
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Table 6:
Combined top quark pole mass at NNLO+NNLL extracted by comparing the measured $ {\mathrm{ t } {}\mathrm{ \bar{t} } } $ production cross section with predictions employing different PDF sets. |
Summary |
A measurement of the inclusive $\mathrm{ t \bar{t} }$ production cross section in proton-proton collisions at the LHC is presented using the full 2011-2012 data samples of 5.0 fb$^{-1}$ at $ \sqrt{s} = $ 7 TeV and 19.7 fb$^{-1}$ at $ \sqrt{s} = $ 8 TeV. The analysis is performed in the ${\mathrm{ e }\mu} $ channel using an improved cross section extraction method. The cross sections are determined with a binned likelihood fit to the $p_{\mathrm{T}}$ distribution of the non-b-tagged jet with the lowest $p_{\mathrm{T}}$ among the selected jets in the event, using categories of number of b-tagged and additional non-b-tagged jets. Assuming a top quark mass of 172.5 GeV, the results are and $ \sigma_{\mathrm{ t \bar{t} }} $ = 244.9 ${\pm}$1.4 (stat) $^{+6.3}_{-5.5}$ (syst) ${\pm}$ 6.4 (lumi) pb, at $\sqrt{s} =$ 8 TeV, in good agreement with recent NNLO QCD calculations. The ratio of the cross sections at the two different values of $\sqrt{s} $ is determined to be 1.41 ${\pm}$ 0.06. Moreover, the cross sections are measured in fiducial ranges defined by the transverse momentum and pseudorapidity requirements on the two charged leptons in the final state. The measurements constitute the most precise CMS results of $\sigma_{\mathrm{ t \bar{t} }} $ so far, and are competitive with recent ATLAS results [14]. The inclusive cross sections at 7 and 8 TeV are used to determine the top quark pole mass via the dependence of the theoretically predicted cross section on the mass, employing three different PDF sets. The values of the mass are consistent between the three sets. The most precise result, 173.8 $^{1.7}_{-1.8}$ GeV, is obtained using the NNPDF3.0 PDF set. The 8 TeV data are also used to constrain the cross section of pair production of supersymmetric top squarks with masses close to the top quark mass. No excess of event yields with respect to the SM prediction is found, and exclusion limits are presented as a function of the top squark mass for two different neutralino masses. |
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