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 CMS collaboration
JHEP 12 (2021) 180, 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 798 $\pm$ 7 (stat) $\pm$ 48 (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 8

    Data from Figure 8

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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 9a

    Data from Figure 9 (top left)

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

  • Figure 9b

    Data from Figure 9 (top right)

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

  • Figure 9c

    Data from Figure 9 (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 10 (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 10 (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 10 (bottom)

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

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

    Additional material: Stat. covariance matrix

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

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

    Additional material: Stat. covariance matrix

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

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

    Additional material: Stat. covariance matrix

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

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

    Additional material: Stat. correlation matrix

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

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

    Additional material: Stat. correlation matrix

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

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

    Additional material: Stat. correlation matrix

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

  • Figure 10a

    Data from Figure 10 (top left)

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

  • Figure 10b

    Data from Figure 10 (top right)

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

  • Figure 10c

    Data from Figure 10 (bottom)

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

  • Table 8

    Table 8

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

  • Figure 11a

    Data from Figure 11 (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 11b

    Data from Figure 11 (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 11c

    Data from Figure 11 (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 11d

    Data from Figure 11 (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 12a

    Data from Figure 12 (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 12b

    Data from Figure 12 (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 12c

    Data from Figure 12 (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 12d

    Data from Figure 12 (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 13

    Data from Figure 13

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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 $c_{tZ}$...

Version 2 modifications: We added an additional uncertainty on the tWgamma background and changed the way we applied Scale uncertainties. This slightly changed the results.

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