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

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 ${\sigma }_{t\bar{t}}=850\pm 3(stat.)\pm 18(syst.)\pm 20(lumi.)$ 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, $R_{t\bar{t}/Z}=1.145\pm 0.003(stat.)\pm 0.021(syst.)\pm 0.002(lumi.)$ is consistent with the Standard Model prediction using the PDF4LHC21 PDF set.

41 pages in total, author list starting page 24, 4 figures, 2 tables, submitted to Phys. Lett. B. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/TOPQ-2023-21/

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• TOP2024: an overview of experimental results
• Measurement of the top-quark production cross-section and charge asymmetry at LHCb
• Inclusive top cross sections in ATLAS