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| CMS-PAS-TOP-14-008 | ||
| Measurement of the $t\bar{t}\text{+}\gamma$ production cross-section in pp collisions at $\sqrt{s}= $ 8 TeV | ||
| CMS Collaboration | ||
| September 2016 | ||
| Abstract: A measurement of the cross section for top quark pairs produced in association with a photon in proton-proton collisions at $\sqrt{s}= $ 8 TeV is presented. The analysis uses data, collected by the CMS detector at the LHC, corresponding to 19.7 $\text{fb}^{-1}$ of integrated luminosity. The signal is defined as the production of a pair of top quarks in association with a photon having a transverse energy of $E_\text{T}> $ 25 GeV and a pseudorapidity of $| \eta |< $ 1.44. The measurement is performed in the fiducial phase space corresponding to the semileptonic decay chain of the top quark pair, and the cross section is measured relative to the inclusive top quark pair production cross section. The ratio of the cross section of top quark pair plus photon production to the top quark pair production cross section is measured to be $\sigma^\text{fid}_{t\bar{t}\text{+}\gamma}/\sigma_{t\bar{t}} =$ 5.2 $\pm$ 1.1 $\times 10^{-4}$ (stat+syst) per semileptonic final state. The fiducial cross section for top quark pair plus photon production is found to be $\sigma^\text{fid}_{t\bar{t}\text{+}\gamma} =$ 127 $\pm$ 27 (stat+syst) fb. | ||
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Links:
CDS record (PDF) ;
inSPIRE record ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, JHEP 10 (2017) 006. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
Feynman diagram for the ${{\mathrm{ t } {}\mathrm{ \bar{t} } } \text {+} \gamma }$ signal process, in the semileptonic final state. |
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Figure 2:
Normalized distributions of the M3 variable for ${{\mathrm{ t } {}\mathrm{ \bar{t} } } \text {+} \gamma }$ events, $ {\mathrm{ t } {}\mathrm{ \bar{t} } } $ events, W+$\gamma $ events, and other background processes in a combination of the $\mathrm{e}$+jets and $\mu$+jets final state after the photon selection. |
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Figure 3:
Comparison of the distribution of the M3 variable in data and simulation, scaled to the result of the fit in a combination of the $\mathrm{e}$+jets and $\mu$+jets channels for events passing the photon selection. The lower portion of the plot shows the ratio of the data to the prediction from theory. The uncertainty band is a combination of statistical and systematic uncertainties on the simulation. |
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Figure 4:
Shapes of isolated photon (left) and hadronic photon (right) templates of the photon charged hadron isolation, comparing data-driven templates to the distributions found from simulation in a combination of the $\mathrm{e}$+jets and $\mu$+jets final states. |
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Figure 4-a:
Shapes of isolated photon templates of the photon charged hadron isolation, comparing data-driven templates to the distributions found from simulation in a combination of the $\mathrm{e}$+jets and $\mu$+jets final states. |
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Figure 4-b:
Shapes of hadronic photon templates of the photon charged hadron isolation, comparing data-driven templates to the distributions found from simulation in a combination of the $\mathrm{e}$+jets and $\mu$+jets final states. |
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Figure 5:
Result of the fit to the photon charged hadron isolation in a combination of the $\mathrm{e}$+jets and $\mu$+jets final states. The uncertainty band is the statistical uncertainties on the data-driven templates. |
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Figure 6:
Result of the template fit to the invariant mass of the electron and photon for events passing the modified event selection with the b tagging requirement relaxed. |
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Figure 7:
Likelihood ratio distributions for $ {\text {SF}_{ {{\mathrm{ t } {}\mathrm{ \bar{t} } } \text {+} \gamma } }} $, $ {\text {SF}_{ {\mathrm {V}\text {+}\gamma } }} $, and ${\text {SF}_{\text {jet}\to \gamma }}$ in a combination of the $\mathrm{e}$+jets and $\mu$+jets final states. |
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Figure 7-a:
Likelihood ratio distributions for $ {\text {SF}_{ {{\mathrm{ t } {}\mathrm{ \bar{t} } } \text {+} \gamma } }} $ in a combination of the $\mathrm{e}$+jets and $\mu$+jets final states. |
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Figure 7-b:
Likelihood ratio distributions for $ {\text {SF}_{ {\mathrm {V}\text {+}\gamma } }} $ in a combination of the $\mathrm{e}$+jets and $\mu$+jets final states. |
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Figure 7-c:
Likelihood ratio distributions for ${\text {SF}_{\text {jet}\to \gamma }}$ in a combination of the $\mathrm{e}$+jets and $\mu$+jets final states. |
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Figure 8:
Comparison of the distribution of the transverse energy of the photon in the event in data and simulation, scaled to the result of the likelihood fit in a combination of the $\mathrm{e}$+jets and $\mu$+jets channels for events passing the photon selection. The lower portion of the plot shows the ratio of the data to the prediction from theory. The uncertainty band is a combination of statistical and systematic uncertainties on the simulation. |
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Figure 9:
Comparison of the distribution of the absolute value of the pseudorapidity of the photon in the event in data and simulation, scaled to the result of the likelihood fit in a combination of the $\mathrm{e}$+jets and $\mu$+jets channels for events passing the photon selection. The lower portion of the plot shows the ratio of the data to the prediction from theory. The uncertainty band is a combination of statistical and systematic uncertainties on the simulation. |
| Tables | |
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Table 1:
Simulated samples categorized by reconstructed photon origin, after photon selection in the $\mathrm{e}$+jets channel. Data driven multijet sample is not expected to have signal photons or electrons. All uncertainties are a combination of statistical and systematic contributions. |
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Table 2:
Simulated samples categorized by reconstructed photon origin, after photon selection in the $\mu$+jets channel. Data driven multijet sample is not expected to have signal photons or electrons. All uncertainties are a combination of statistical and systematic contributions. |
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Table 3:
Scale factors found to maximize the likelihood function in the $\mathrm{e}$+jets channel, $\mu$+jets channel, and the combination of the two semileptonic channels. The uncertainties are statistical in nature. |
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Table 4:
Efficiency and acceptance of the ${{\mathrm{ t } {}\mathrm{ \bar{t} } } \text {+} \gamma }$ selection in the $\mathrm{e}$+jets and $\mu$+jets final states. |
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Table 5:
Systematic uncertainties and their contribution to the cross section ratio in the combination of the $\mathrm{e}$+jets and $\mu$+jets final states. |
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Table 6:
Measured values of the cross section ratio as well as fiducial cross sections. |
| Summary |
| The results of the measurement of the production of a top quark pair produced in association with a photon have been presented. The measurement was performed using 19.7 fb$^{-1}$ of data collected by the CMS detector at a center of mass energy of 8 TeV. The analysis is performed in the semileptonic $\mathrm{e}$+jets and $\mu$+jets decay channels. The ratio of the ${\mathrm{ t \bar{t} } \text{+} \gamma}$ to $\mathrm{ t \bar{t} } $production cross sections is measured to be $R={\sigma_{{\mathrm{ t \bar{t} } \text{+} \gamma} }/\sigma_{\mathrm{ t \bar{t} }}}= $ 5.2 $\pm$ 1.1 $\times 10^{-4}$ (stat+syst). By multiplying the measured ratio by the previously measured value of the $\mathrm{ t \bar{t} }$ cross section, the fiducial cross section for ${\mathrm{ t \bar{t} } \text{+} \gamma} $ production of 27 $\pm$ 27 (stat+syst) fb is found for events in the $\mathrm{e}$+jets and $\mu$+jets final states. |
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