Measurement of the $t\bar{t}$ cross section and its ratio to the $Z$ production cross section using $pp$ collisions at $\sqrt{s} = 13.6$ TeV with the ATLAS detector

The ATLAS collaboration
Phys.Lett.B 848 (2024) 138376, 2024.

Abstract
The inclusive top-quark-pair production cross section $\sigma_{t\bar{t}}$ and its ratio to the $Z$-boson production cross section have been measured in proton--proton collisions at $\sqrt{s} = 13.6$ TeV, using 29 fb${}^{-1}$ of data collected in 2022 with the ATLAS experiment at the Large Hadron Collider. Using events with an opposite-charge electron-muon pair and $b$-tagged jets, and assuming Standard Model decays, the top-quark-pair production cross section is measured to be $\sigma_{t\bar{t}} = 850 \pm 3\mathrm{(stat.)}\pm 18\mathrm{(syst.)}\pm 20\mathrm{(lumi.)}$ pb. The ratio of the $t\bar{t}$ and the $Z$-boson production cross sections is also measured, where the $Z$-boson contribution is determined for inclusive $e^+e^-$ and $\mu^+\mu^-$ events in a fiducial phase space. The relative uncertainty on the ratio is reduced compared to the $t\bar{t}$ cross section, thanks to the cancellation of several systematic uncertainties. The result for the ratio, $R_{t\bar{t}/Z} = 1.145 \pm 0.003\mathrm{(stat.)}\pm 0.021\mathrm{(syst.)}\pm 0.002\mathrm{(lumi.)}$ is consistent with the Standard Model prediction using the PDF4LHC21 PDF set.

  • $Z$-boson phase-space

    10.17182/hepdata.143515.v1/t1

    The fiducial phase-space definition for the $Z$-boson measurement. Born-level leptons are used.

  • Cross section and ratio results

    10.17182/hepdata.143515.v1/t2

    The measured $t\bar{t}$ cross section and the ratio of the cross sections of $t\bar{t}$ and the $Z$-boson. Full phase-space is...

  • Pre-fit yields

    Data from Figure 2 (left)

    10.17182/hepdata.143515.v1/t3

    Table with pre-fit yields in the four regions used in the measurement

  • Post-fit yields

    Data from Figure 2 (right)

    10.17182/hepdata.143515.v1/t4

    Table with post-fit yields in the four regions used in the measurement. The correlations of the nuisance parameters, as obtained...

  • Cross section ratio theory comparison

    Data from Figure 4

    10.17182/hepdata.143515.v1/t5

    Ratio of the $t\bar{t}$ to the $Z$-boson cross section compared to the predictions for several sets of parton distribution functions....

  • $t\bar{t}$ cross section nuisance parameter ranking

    Data from Figure 5 of the Auxiliary material

    10.17182/hepdata.143515.v1/t6

    Nuisance parameter ranking plot for the $t\bar{t}$ signal-strength. Only the 10 most important nuisance parameters are shown. The impact of...

  • Cross section ratio nuisance parameter ranking

    Data from Figure 6 of the Auxiliary material

    10.17182/hepdata.143515.v1/t7

    Nuisance parameter ranking plot for the ratio of the $t\bar{t}$ and $Z$-boson signal-strengths. Only the 10 most important nuisance parameters...

  • $Z$-boson cross section nuisance parameter ranking

    Data from Figure 7 of the Auxiliary material

    10.17182/hepdata.143515.v1/t8

    Nuisance parameter ranking plot for the $Z$-boson signal-strength. Only the 10 most important nuisance parameters are shown. The impact of...

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