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Measurement of the inclusive and differential $\mathrm{t\overline{t}}\gamma$ cross sections in the single-lepton channel and EFT interpretation at $\sqrt{s}$ = 13 TeV

The collaboration
CMS-TOP-18-010, 2021.

Abstract
The production cross section of a top quark pair in association with a photon is measured in proton-proton collisions at a center-of-mass energy of 13 TeV. The data set, corresponding to an integrated luminosity of 137 fb$^{-1}$, was recorded by the CMS experiment during the 2016-2018 data taking of the LHC. The measurements are performed in a fiducial volume defined at the particle level. Events with an isolated, highly energetic lepton, at least three jets from the hadronization of quarks, among which at least one is b tagged, and one isolated photon are selected. The inclusive fiducial $\mathrm{t\overline{t}}\gamma$ cross section, for a photon with transverse momentum greater than 20 GeV and pseudorapidity $\lvert \eta\rvert \lt$ 1.4442, is measured to be 800 $\pm$ 7 (stat) $\pm$ 46 (syst) fb, in good agreement with the prediction from the standard model at next-to-leading order in quantum chromodynamics. The differential cross sections are also measured as a function of several kinematic observables and interpreted in the framework of the standard model effective field theory (EFT), leading to the most stringent direct limits to date on anomalous electromagnetic dipole moment interactions of the top quark and the photon.

• #### Figure 2a

Data from Figure 2 (top left)

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Distribution of $p_{T}(\gamma)$ in the $N_{jet}\geq 3$ signal region.

• #### Figure 2b

Data from Figure 2 (top center)

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Distribution of $m_{T}(W)$ in the $N_{jet}\geq 3$ signal region.

• #### Figure 2c

Data from Figure 2 (top right)

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Distribution of $M_{3}$ in the $N_{jet}\geq 3$ signal region.

• #### Figure 2d

Data from Figure 2 (bottom left)

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Distribution of $m(l,\gamma)$ in the $N_{jet}\geq 3$ signal region.

• #### Figure 2e

Data from Figure 2 (bottom center)

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Distribution of $\Delta R(l,\gamma)$ in the $N_{jet}\geq 3$ signal region.

• #### Figure 2f

Data from Figure 2 (bottom right)

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Distribution of $\Delta R(j,\gamma)$ in the $N_{jet}\geq 3$ signal region.

• #### Figure 3a

Data from Figure 3 (left)

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Fit result of the multijet template obtained with loosely isolated leptons and the electroweak background to the measured $m_{T}(W)$ distribution...

• #### Figure 3b

Data from Figure 3 (right)

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Fit result of the multijet template obtained with loosely isolated leptons and the electroweak background to the measured $m_{T}(W)$ distribution...

• #### Figure 4a

Data from Figure 4 (left)

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Distribution of the invariant mass of the lepton and the photon ($m(l,\gamma)$) in the $N_{jet}\geq 3$, $N_{b jet}=0$ selection for...

• #### Figure 4b

Data from Figure 4 (right)

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Distribution of the invariant mass of the lepton and the photon ($m(l,\gamma)$) in the $N_{jet}\geq 3$, $N_{b jet}=0$ selection for...

• #### Table 4

Table 4

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Extracted scale factors for the contribution from misidentified electrons for the three data-taking periods, and the Z$\gamma$, W$\gamma$ simulations.

• #### Figure 5

Data from Figure 5

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Predicted and observed yields in the control regions in the $N_{jet}= 3$ and $\geq 4$ seletions using the post-fit values...

• #### Figure 6

Data from Figure 6

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Predicted and observed yields in the signal regions in the $N_{jet}= 3$ and $\geq 4$ seletions using the post-fit values...

• #### Equation 2

Equation 2

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The measured inclusive ttgamma cross section in the fiducial phase space compared to the prediction from simulation using Madgraph_aMC@NLO at...

• #### Figure 7

Data from Figure 7

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Summary of the measured cross section ratios with respect to the NLO cross section prediction for signal regions binned in...

• #### Figure 8a

Data from Figure 8 (top left)

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The unfolded differential cross sections for $p_{T}(\gamma)$ and the comparison to simulations.

• #### Figure 8b

Data from Figure 8 (top right)

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The unfolded differential cross sections for $|\eta(\gamma)|$ and the comparison to simulations.

• #### Figure 8c

Data from Figure 8 (bottom)

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The unfolded differential cross sections for $\Delta R(l,\gamma)$ and the comparison to simulations.

• #### Syst. covariance matrix $p_{T}(\gamma)$

Additional material: Covariance matrix to Figure 9 (top left)

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The covariance matrix of systematic uncertainties for the unfolded differential measurement for $p_{T}(\gamma)$.

• #### Syst. covariance matrix $|\eta(\gamma)|$

Additional material: Covariance matrix to Figure 9 (top right)

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The covariance matrix of systematic uncertainties for the unfolded differential measurement for $|\eta(\gamma)|$.

• #### Syst. covariance matrix $\Delta R(l,\gamma)$

Additional material: Covariance matrix to Figure 9 (bottom)

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The covariance matrix of systematic uncertainties for the unfolded differential measurement for $\Delta R(l,\gamma)$.

• #### Stat. covariance matrix $p_{T}(\gamma)$

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The covariance matrix of statistic uncertainties for the unfolded differential measurement for $p_{T}(\gamma)$.

• #### Stat. covariance matrix $|\eta(\gamma)|$

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The covariance matrix of statistic uncertainties for the unfolded differential measurement for $|\eta(\gamma)|$.

• #### Stat. covariance matrix $\Delta R(l,\gamma)$

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The covariance matrix of statistic uncertainties for the unfolded differential measurement for $\Delta R(l,\gamma)$.

• #### Stat. correlation matrix $p_{T}(\gamma)$

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The correlation matrix of statistical uncertainties for the unfolded differential measurement for $p_{T}(\gamma)$.

• #### Stat. correlation matrix $|\eta(\gamma)|$

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The correlation matrix of statistical uncertainties for the unfolded differential measurement for $|\eta(\gamma)|$.

• #### Stat. correlation matrix $\Delta R(l,\gamma)$

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The correlation matrix of statistical uncertainties for the unfolded differential measurement for $\Delta R(l,\gamma)$.

• #### Figure 9a

Data from Figure 9 (top left)

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The correlation matrix of systematic uncertainties for the unfolded differential measurement for $p_{T}(\gamma)$.

• #### Figure 9b

Data from Figure 9 (top right)

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The correlation matrix of systematic uncertainties for the unfolded differential measurement for $|\eta(\gamma)|$.

• #### Figure 9c

Data from Figure 9 (bottom)

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The correlation matrix of systematic uncertainties for the unfolded differential measurement for $\Delta R(l,\gamma)$.

• #### Table 7

Table 7

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Summary of the one-dimensional intervals at 68 and 95% CL.

• #### Figure 10a

Data from Figure 10 (top left)

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The observed and predicted post-fit yields for the combined Run 2 data set in the SR3 signal region for the...

• #### Figure 10b

Data from Figure 10 (top right)

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The observed and predicted post-fit yields for the combined Run 2 data set in the SR3 signal region for the...

• #### Figure 10c

Data from Figure 10 (bottom left)

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The observed and predicted post-fit yields for the combined Run 2 data set in the SR4p signal region for the...

• #### Figure 10d

Data from Figure 10 (bottom right)

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The observed and predicted post-fit yields for the combined Run 2 data set in the SR4p signal region for the...

• #### Figure 11a

Data from Figure 11 (top left)

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Negative log-likelihood ratio values with respect to the best fit value of the one-dimensional profiled scan for the Wilson coefficient...

• #### Figure 11b

Data from Figure 11 (top right)

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Negative log-likelihood ratio values with respect to the best fit value of the one-dimensional profiled scan for the Wilson coefficient...

• #### Figure 11c

Data from Figure 11 (bottom left)

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Negative log-likelihood ratio values with respect to the best fit value of the one-dimensional scan for the Wilson coefficient $c_{tZ}$.

• #### Figure 11d

Data from Figure 11 (bottom right)

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Negative log-likelihood ratio values with respect to the best fit value of the one-dimensional scan for the Wilson coefficient $c^{I}_{tZ}$.

• #### Figure 12

Data from Figure 12

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Negative log-likelihood ratio values with respect to the best fit value of the two-dimensional scan for the Wilson coefficients $c_{tZ}$...