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| CMS-PAS-TOP-18-010 | ||
| Measurement of the inclusive and differential $\mathrm{t}\bar{\mathrm{t}} + \gamma$ cross section and EFT interpretation in the single lepton channel at $\sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| March 2021 | ||
| Abstract: The production cross section of a top quark pair in association with a photon is measured in proton-proton collisions at the center-of-mass energy of 13 TeV. The data set of 137 fb$^{-1}$ was recorded by the CMS experiment during the LHC Run II. The measurement is performed in events with a well isolated, highly energetic lepton (electron or muon), with at least three jets from the hadronization of quarks and one isolated photon. The photon may be emitted from initial state radiation, from the top quarks, as well as from decay products of the top quarks. The analysis makes use of simultaneous likelihood fits in several signal and control regions to distinguish the $\mathrm{t}\bar{\mathrm{t}} + \gamma$ signal process from various backgrounds. The inclusive cross section for a photon with transverse momentum of $\mathrm{p}_\mathrm{T} \geq$ 20 GeV is measured as 800 $\pm$ 46 (syst) $\pm$ 7 (stat) fb, in good agreement with the prediction from the standard model. The measurement is also carried out differentially in several kinematic observables and interpreted in the framework of the standard model effective field theory. | ||
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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These preliminary results are superseded in this paper, Submitted to JHEP. The superseded preliminary plots can be found here.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:
Representative LO Feynman diagrams for the ${{\mathrm{t} \mathrm{\bar{t}}} \gamma}$ signal process in the single lepton channel where the high energetic photon originates from the top quark (left, middle), or is emitted from a lepton (right). The $\mathrm{t} \gamma $ interaction is indicated by a circle. |
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Figure 1-a:
Representative LO Feynman diagrams for the ${{\mathrm{t} \mathrm{\bar{t}}} \gamma}$ signal process in the single lepton channel where the high energetic photon originates from the top quark (left, middle), or is emitted from a lepton (right). The $\mathrm{t} \gamma $ interaction is indicated by a circle. |
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Figure 1-b:
Representative LO Feynman diagrams for the ${{\mathrm{t} \mathrm{\bar{t}}} \gamma}$ signal process in the single lepton channel where the high energetic photon originates from the top quark (left, middle), or is emitted from a lepton (right). The $\mathrm{t} \gamma $ interaction is indicated by a circle. |
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Figure 1-c:
Representative LO Feynman diagrams for the ${{\mathrm{t} \mathrm{\bar{t}}} \gamma}$ signal process in the single lepton channel where the high energetic photon originates from the top quark (left, middle), or is emitted from a lepton (right). The $\mathrm{t} \gamma $ interaction is indicated by a circle. |
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Figure 2:
Distribution of ${p_{T}(\gamma)}$, the transverse mass ${{m_{\mathrm {T}}} (\mathrm{W})}$ of the W boson candidate, the three-jet invariant mass ${M_3}$ (upper row) and the invariant mass of the lepton and the photon ($m(\ell,\gamma)$), the angular separation of the lepton and the photon ($\Delta R(\ell,\gamma)$), and the angular separation of the leading jet and the photon ($\Delta R(j_1, \gamma)$) (lower row). The lower panels show the ratio of the observation to the prediction. The systematic uncertainties are shown as a shaded band. |
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Figure 2-a:
Distribution of ${p_{T}(\gamma)}$, the transverse mass ${{m_{\mathrm {T}}} (\mathrm{W})}$ of the W boson candidate, the three-jet invariant mass ${M_3}$ (upper row) and the invariant mass of the lepton and the photon ($m(\ell,\gamma)$), the angular separation of the lepton and the photon ($\Delta R(\ell,\gamma)$), and the angular separation of the leading jet and the photon ($\Delta R(j_1, \gamma)$) (lower row). The lower panels show the ratio of the observation to the prediction. The systematic uncertainties are shown as a shaded band. |
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Figure 2-b:
Distribution of ${p_{T}(\gamma)}$, the transverse mass ${{m_{\mathrm {T}}} (\mathrm{W})}$ of the W boson candidate, the three-jet invariant mass ${M_3}$ (upper row) and the invariant mass of the lepton and the photon ($m(\ell,\gamma)$), the angular separation of the lepton and the photon ($\Delta R(\ell,\gamma)$), and the angular separation of the leading jet and the photon ($\Delta R(j_1, \gamma)$) (lower row). The lower panels show the ratio of the observation to the prediction. The systematic uncertainties are shown as a shaded band. |
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Figure 2-c:
Distribution of ${p_{T}(\gamma)}$, the transverse mass ${{m_{\mathrm {T}}} (\mathrm{W})}$ of the W boson candidate, the three-jet invariant mass ${M_3}$ (upper row) and the invariant mass of the lepton and the photon ($m(\ell,\gamma)$), the angular separation of the lepton and the photon ($\Delta R(\ell,\gamma)$), and the angular separation of the leading jet and the photon ($\Delta R(j_1, \gamma)$) (lower row). The lower panels show the ratio of the observation to the prediction. The systematic uncertainties are shown as a shaded band. |
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Figure 2-d:
Distribution of ${p_{T}(\gamma)}$, the transverse mass ${{m_{\mathrm {T}}} (\mathrm{W})}$ of the W boson candidate, the three-jet invariant mass ${M_3}$ (upper row) and the invariant mass of the lepton and the photon ($m(\ell,\gamma)$), the angular separation of the lepton and the photon ($\Delta R(\ell,\gamma)$), and the angular separation of the leading jet and the photon ($\Delta R(j_1, \gamma)$) (lower row). The lower panels show the ratio of the observation to the prediction. The systematic uncertainties are shown as a shaded band. |
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Figure 2-e:
Distribution of ${p_{T}(\gamma)}$, the transverse mass ${{m_{\mathrm {T}}} (\mathrm{W})}$ of the W boson candidate, the three-jet invariant mass ${M_3}$ (upper row) and the invariant mass of the lepton and the photon ($m(\ell,\gamma)$), the angular separation of the lepton and the photon ($\Delta R(\ell,\gamma)$), and the angular separation of the leading jet and the photon ($\Delta R(j_1, \gamma)$) (lower row). The lower panels show the ratio of the observation to the prediction. The systematic uncertainties are shown as a shaded band. |
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Figure 2-f:
Distribution of ${p_{T}(\gamma)}$, the transverse mass ${{m_{\mathrm {T}}} (\mathrm{W})}$ of the W boson candidate, the three-jet invariant mass ${M_3}$ (upper row) and the invariant mass of the lepton and the photon ($m(\ell,\gamma)$), the angular separation of the lepton and the photon ($\Delta R(\ell,\gamma)$), and the angular separation of the leading jet and the photon ($\Delta R(j_1, \gamma)$) (lower row). The lower panels show the ratio of the observation to the prediction. The systematic uncertainties are shown as a shaded band. |
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Figure 3:
Fit result of the multijet template obtained with loosely isolated leptons and the electroweak background to the measured ${{m_{\mathrm {T}}} (\mathrm{W})}$ distribution with isolated leptons in the $ {N_\text {jet}} =$ 2, $ {N_\text {b jet}} =$ 0 selection for electrons (left) and muons (right). The lower panels show the ratio of the observation to the prediction. The systematic uncertainties are shown as a shaded band. |
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Figure 3-a:
Fit result of the multijet template obtained with loosely isolated leptons and the electroweak background to the measured ${{m_{\mathrm {T}}} (\mathrm{W})}$ distribution with isolated leptons in the $ {N_\text {jet}} =$ 2, $ {N_\text {b jet}} =$ 0 selection for electrons (left) and muons (right). The lower panels show the ratio of the observation to the prediction. The systematic uncertainties are shown as a shaded band. |
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Figure 3-b:
Fit result of the multijet template obtained with loosely isolated leptons and the electroweak background to the measured ${{m_{\mathrm {T}}} (\mathrm{W})}$ distribution with isolated leptons in the $ {N_\text {jet}} =$ 2, $ {N_\text {b jet}} =$ 0 selection for electrons (left) and muons (right). The lower panels show the ratio of the observation to the prediction. The systematic uncertainties are shown as a shaded band. |
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Figure 4:
Distribution of the invariant mass of the lepton and the photon ($m(\ell,\gamma)$) in the $ {N_\text {jet}} \geq $ 3, $ {N_\text {b jet}} =$ 0 selection for the e channel (left) and the $\mu$channel (right). The lower panels show the ratio of the observation to the prediction. The systematic uncertainties are shown as a shaded band. |
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Figure 4-a:
Distribution of the invariant mass of the lepton and the photon ($m(\ell,\gamma)$) in the $ {N_\text {jet}} \geq $ 3, $ {N_\text {b jet}} =$ 0 selection for the e channel (left) and the $\mu$channel (right). The lower panels show the ratio of the observation to the prediction. The systematic uncertainties are shown as a shaded band. |
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Figure 4-b:
Distribution of the invariant mass of the lepton and the photon ($m(\ell,\gamma)$) in the $ {N_\text {jet}} \geq $ 3, $ {N_\text {b jet}} =$ 0 selection for the e channel (left) and the $\mu$channel (right). The lower panels show the ratio of the observation to the prediction. The systematic uncertainties are shown as a shaded band. |
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Figure 5:
Predicted yields and observation in the control regions in the $ {N_\text {jet}} =$ 3 and $ {N_\text {jet}} \geq $ 4 selections for post-fit values of the nuisance parameters. The lower panels show the ratio of the observation to the prediction. The shaded bands show the systematic uncertainty in the background prediction. |
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Figure 6:
Predicted yields and observation in the signal regions in the $ {N_\text {jet}} =$ 3 and $ {N_\text {jet}} \geq $ 4 selections for post-fit values of the nuisance parameters. The lower panels show the ratio of the observation to the prediction. The systematic uncertainties are shown as a shaded band. |
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Figure 7:
Summary of the measured cross sections normalized to the NLO cross section prediction for signal regions binned in the e-channel, $\mu $-channel and the combined single lepton measurement. The light brown band indicates the theory uncertainty in the prediction. |
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Figure 8:
The distribution of ${p_{T}(\gamma)}$ (left), ${|\eta (\gamma)|}$ (right), and ${\Delta R(\ell,\gamma)}$ (bottom) in the $ {N_\text {jet}} \geq $ 3 selection after background subtraction. The lower panel displays the relative uncertainty, where the inner and outer bands show the statistical and total uncertainties, respectively. |
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Figure 8-a:
The distribution of ${p_{T}(\gamma)}$ (left), ${|\eta (\gamma)|}$ (right), and ${\Delta R(\ell,\gamma)}$ (bottom) in the $ {N_\text {jet}} \geq $ 3 selection after background subtraction. The lower panel displays the relative uncertainty, where the inner and outer bands show the statistical and total uncertainties, respectively. |
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Figure 8-b:
The distribution of ${p_{T}(\gamma)}$ (left), ${|\eta (\gamma)|}$ (right), and ${\Delta R(\ell,\gamma)}$ (bottom) in the $ {N_\text {jet}} \geq $ 3 selection after background subtraction. The lower panel displays the relative uncertainty, where the inner and outer bands show the statistical and total uncertainties, respectively. |
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Figure 8-c:
The distribution of ${p_{T}(\gamma)}$ (left), ${|\eta (\gamma)|}$ (right), and ${\Delta R(\ell,\gamma)}$ (bottom) in the $ {N_\text {jet}} \geq $ 3 selection after background subtraction. The lower panel displays the relative uncertainty, where the inner and outer bands show the statistical and total uncertainties, respectively. |
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Figure 9:
The unfolded differential cross sections for ${p_{T}(\gamma)}$ (left), ${|\eta (\gamma)|}$ (right), and ${\Delta R(\ell,\gamma)}$ (bottom). The lower panel displays the ratio of simulation to the observation. The inner and outer bands show the statistical and total uncertainties, respectively. |
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Figure 9-a:
The unfolded differential cross sections for ${p_{T}(\gamma)}$ (left), ${|\eta (\gamma)|}$ (right), and ${\Delta R(\ell,\gamma)}$ (bottom). The lower panel displays the ratio of simulation to the observation. The inner and outer bands show the statistical and total uncertainties, respectively. |
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Figure 9-b:
The unfolded differential cross sections for ${p_{T}(\gamma)}$ (left), ${|\eta (\gamma)|}$ (right), and ${\Delta R(\ell,\gamma)}$ (bottom). The lower panel displays the ratio of simulation to the observation. The inner and outer bands show the statistical and total uncertainties, respectively. |
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Figure 9-c:
The unfolded differential cross sections for ${p_{T}(\gamma)}$ (left), ${|\eta (\gamma)|}$ (right), and ${\Delta R(\ell,\gamma)}$ (bottom). The lower panel displays the ratio of simulation to the observation. The inner and outer bands show the statistical and total uncertainties, respectively. |
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Figure 10:
The covariance matrices of the unfolded differential measurement for ${p_{T}(\gamma)}$ (left), ${|\eta (\gamma)|}$ (right), and ${\Delta R(\ell,\gamma)}$ (bottom). |
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Figure 10-a:
The covariance matrices of the unfolded differential measurement for ${p_{T}(\gamma)}$ (left), ${|\eta (\gamma)|}$ (right), and ${\Delta R(\ell,\gamma)}$ (bottom). |
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Figure 10-b:
The covariance matrices of the unfolded differential measurement for ${p_{T}(\gamma)}$ (left), ${|\eta (\gamma)|}$ (right), and ${\Delta R(\ell,\gamma)}$ (bottom). |
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Figure 10-c:
The covariance matrices of the unfolded differential measurement for ${p_{T}(\gamma)}$ (left), ${|\eta (\gamma)|}$ (right), and ${\Delta R(\ell,\gamma)}$ (bottom). |
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Figure 11:
Results of one-dimensional scans for the Wilson coefficients ${c_{\mathrm{t} \mathrm{Z}}}$ (left) and ${c_{\mathrm{t} \mathrm{Z}}^{I}}$ (right), and for the two-dimensional plane (bottom). The shading quantified by the color scale on the right reflects the negative log-likelihood ratio with respect to the best-fit value that is designated by the star. The green and orange lines indicate the 68 and 95% CL contours from the fit, respectively. The allowed areas are those between the two green contours and that inside the orange contour. The dot shows the SM prediction. |
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Figure 11-a:
Results of one-dimensional scans for the Wilson coefficients ${c_{\mathrm{t} \mathrm{Z}}}$ (left) and ${c_{\mathrm{t} \mathrm{Z}}^{I}}$ (right), and for the two-dimensional plane (bottom). The shading quantified by the color scale on the right reflects the negative log-likelihood ratio with respect to the best-fit value that is designated by the star. The green and orange lines indicate the 68 and 95% CL contours from the fit, respectively. The allowed areas are those between the two green contours and that inside the orange contour. The dot shows the SM prediction. |
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Figure 11-b:
Results of one-dimensional scans for the Wilson coefficients ${c_{\mathrm{t} \mathrm{Z}}}$ (left) and ${c_{\mathrm{t} \mathrm{Z}}^{I}}$ (right), and for the two-dimensional plane (bottom). The shading quantified by the color scale on the right reflects the negative log-likelihood ratio with respect to the best-fit value that is designated by the star. The green and orange lines indicate the 68 and 95% CL contours from the fit, respectively. The allowed areas are those between the two green contours and that inside the orange contour. The dot shows the SM prediction. |
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Figure 11-c:
Results of one-dimensional scans for the Wilson coefficients ${c_{\mathrm{t} \mathrm{Z}}}$ (left) and ${c_{\mathrm{t} \mathrm{Z}}^{I}}$ (right), and for the two-dimensional plane (bottom). The shading quantified by the color scale on the right reflects the negative log-likelihood ratio with respect to the best-fit value that is designated by the star. The green and orange lines indicate the 68 and 95% CL contours from the fit, respectively. The allowed areas are those between the two green contours and that inside the orange contour. The dot shows the SM prediction. |
| Tables | |
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Table 1:
Event generator and orders of accuracy for each simulated process. |
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Table 2:
Overview of signal and control regions. For ZG, WG, and misDY the regions with suffixes 3 (4p) have a modified jet multiplicity requirement of $ {N_\text {jet}} =$ 3 ($ {N_\text {jet}} \geq $ 4). |
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Table 3:
Extracted scale factors for the contribution from misidentified electrons for the three data taking periods, and the ${{\mathrm{Z}} \gamma}, {\mathrm{W} \gamma}$ scale factors. |
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Table 4:
Summary of systematic uncertainties. The first column indicates the source of the uncertainty. The second column shows the correlation between the data taking periods, where the check symbol indicates 100% correlation. The third column shows the typical pre-fit uncertainties in the simulated yields of the signal region. The last column gives the corresponding systematic uncertainty in the ${{\mathrm{t} \mathrm{\bar{t}}} \gamma}$ cross section using the fit result. |
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Table 5:
Binning choices in the differential measurements. |
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Table 6:
Summary of the 1D confidence intervals at 68 and 95% CL. |
| Summary |
|
A measurement of top quark pair production in association with a photon using a data sample of proton-proton collisions at $\sqrt{s} = $ 13 TeV, corresponding to an integrated luminosity of 137 fb$^{-1}$, collected with the CMS detector at the LHC has been presented. The analysis was performed in the three- and at least four-jet final states. A data driven approach is used to estimate the background in the signal regions. The measured inclusive cross section is $\sigma^{\textrm{fid.}}({\mathrm{t\bar{t}}\gamma} ) = $ 800 $\pm$ 46 (syst) $\pm$ 7 (stat) fb and is in good agreement with the standard model prediction. Absolute and normalized differential cross sections for the transverse momentum of the ${p_{\mathrm{T}}}(\gamma)$, ${|\eta(\gamma)|}$, and ${\Delta R(\ell,\gamma)}$ are measured. The measurement is also interpreted in terms of Wilson coefficients in the context of SMEFT. The confidence intervals for the Wilson coefficients ${c_{\mathrm{t}\mathrm{Z}}} $ and ${c_{\mathrm{t}\mathrm{Z}}^{I}} $ are the strongest to date. |
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