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SpringerOpen, The European Physical Journal C, 6(80), 2020

DOI: 10.1140/epjc/s10052-020-7907-9

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Measurement of the $t\bar{t}$ production cross-section and lepton differential distributions in $eμ $ dilepton events from $pp$ collisions at $\sqrt{s}=13\,\text {TeV}$ with the ATLAS detector

Journal article published in 2020 by Georges Aad ORCID, Braden Abbott, Dale Charles Abbott, A. Abed Abud, Adam Abed Abud, Kira Abeling, Deshan Kavishka Abhayasinghe, Syed Haider Abidi, Ossama Sherif Alexander AbouZeid, Nicola L. Abraham, Halina Abramowicz, Henso Abreu, Yiming Abulaiti, Bobby S. Acharya, Baida Achkar and other authors.
This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

AbstractThe inclusive top quark pair ($t\bar{t}$ t t ¯ ) production cross-section $σ _{t\bar{t}}$ σ t t ¯ has been measured in proton–proton collisions at $\sqrt{s}=13\,\text {TeV}$ s = 13 TeV , using 36.1 fb$^{-1}$ - 1 of data collected in 2015–2016 by the ATLAS experiment at the LHC. Using events with an opposite-charge $eμ $ e μ pair and b-tagged jets, the cross-section is measured to be: $\begin{aligned} σ _{t\bar{t}} = 826.4 ± 3.6\,\mathrm {(stat)}\ ± 11.5\,\mathrm {(syst)}\ ± 15.7\,\mathrm {(lumi)}\ ± 1.9\,\mathrm {(beam)}\,\mathrm {pb}, \end{aligned}$ σ t t ¯ = 826.4 ± 3.6 ( stat ) ± 11.5 ( syst ) ± 15.7 ( lumi ) ± 1.9 ( beam ) pb , where the uncertainties reflect the limited size of the data sample, experimental and theoretical systematic effects, the integrated luminosity, and the LHC beam energy, giving a total uncertainty of 2.4%. The result is consistent with theoretical QCD calculations at next-to-next-to-leading order. It is used to determine the top quark pole mass via the dependence of the predicted cross-section on $m_t^{\mathrm{pole}}$ m t pole , giving $m_t^{\mathrm{pole}}=173.1^{+2.0}_{-2.1}\,\text {GeV}$ m t pole = 173 . 1 - 2.1 + 2.0 GeV . It is also combined with measurements at $\sqrt{s}=7\,\text {TeV}$ s = 7 TeV and $\sqrt{s}=8\,\text {TeV}$ s = 8 TeV to derive ratios and double ratios of $t\bar{t}$ t t ¯ and Z cross-sections at different energies. The same event sample is used to measure absolute and normalised differential cross-sections as functions of single-lepton and dilepton kinematic variables, and the results are compared with predictions from various Monte Carlo event generators.