Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Observation of $t\bar{t}γγ$ production at $\sqrt{s}=$13 TeV with the ATLAS detector

ATLAS Collaboration

Abstract

This paper presents the first observation of top-quark pair production in association with two photons ($t\bar{t}γγ$). The measurement is performed in the single-lepton decay channel using proton-proton collision data collected by the ATLAS detector at the Large Hadron Collider. The data correspond to an integrated luminosity of 140 fb$^{-1}$ recorded during Run 2 at a centre-of-mass energy of 13 TeV. The $t\bar{t}γγ$ production cross section, measured in a fiducial phase space based on particle-level kinematic criteria for the lepton, photons, and jets, is found to be $2.42^{+0.58}_{-0.53}\, \text{fb}$, corresponding to an observed significance of 5.2 standard deviations. Additionally, the ratio of the production cross section of $t\bar{t}γγ$ to top-quark pair production in association with one photon is determined, yielding $(3.30^{+0.70}_{-0.65})\times 10^{-3}$.

Observation of $t\bar{t}γγ$ production at $\sqrt{s}=$13 TeV with the ATLAS detector

Abstract

This paper presents the first observation of top-quark pair production in association with two photons (). The measurement is performed in the single-lepton decay channel using proton-proton collision data collected by the ATLAS detector at the Large Hadron Collider. The data correspond to an integrated luminosity of 140 fb recorded during Run 2 at a centre-of-mass energy of 13 TeV. The production cross section, measured in a fiducial phase space based on particle-level kinematic criteria for the lepton, photons, and jets, is found to be , corresponding to an observed significance of 5.2 standard deviations. Additionally, the ratio of the production cross section of to top-quark pair production in association with one photon is determined, yielding .

Paper Structure

This paper contains 7 sections, 1 equation, 3 figures, 1 table.

Table of Contents

  1. Introduction
  2. ATLAS detector
  3. Modelling of signal and background processes
  4. Event selection and background estimate
  5. Systematic uncertainties
  6. Measurement of the $t\bar{t}\gamma\gamma$ cross section and $t\bar{t}\gamma\gamma$/$t\bar{t}\gamma$ cross-section ratio
  7. Conclusion

Figures (3)

  • Figure 1: Examples of leading-order Feynman diagrams for $t\bar{t}\gamma\gamma$ production in the single-lepton final state, where the photons are radiated by (a) an off-shell top quark and the charged lepton and (b) an initial-state quark and the charged lepton, respectively.
  • Figure 2: Example of input variables with large separation power, before the fit to data: (a) conversion type of the photon leading in $p_{\text{T}}$, (b) $\Delta R$ between the lepton and the subleading photon in $p_{\text{T}}$ and (c) their invariant mass. The uncertainty band corresponds to the total uncertainties before the fit to data. The lower part of the plot shows the ratio of the data to the prediction. If present, overflow events are included in the last bin of the distribution. The 'Other $\gamma\gamma$' category includes simulated events with two prompt photons from single-top quark, single and diboson processes, $t\bar{t}V$, $t\bar{t}H$, and $\Pqt{}\Paqt$ samples. The normalisation of the $t\bar{t}\gamma\gamma$ sample is rescaled using the NLO/LO $K$-factor described in Section \ref{['sec:simulations']}.
  • Figure 3: BDT distribution output after the fit to data. The uncertainty band corresponds to the total uncertainties with correlations among uncertainties taken into account as determined in the fit. The lower part of the plot shows the ratio of the data to the prediction. The 'Other $\gamma\gamma$' category includes simulated events with two prompt photons from single-top quark, single and diboson processes, $t\bar{t}V$, $t\bar{t}H$, and $\Pqt{}\Paqt$ samples.