The top anti-top quark production cross-section is measured in the lepton+jets channel using proton–proton collision data at a centre-of-mass energy of √s=13 TeV collected with the ATLAS detector at the LHC. The dataset corresponds to an integrated luminosity of 139 fb−1. Events with exactly one charged lepton and four or more jets in the final state, with at least one jet containing b-hadrons, are used to determine the t ̄tproduction cross-section through a profile-likelihood fit. The inclusive cross-section is measured to be σinc=830±0.4(stat.)±36 (syst.)±14 (lumi.) pb with a relative uncertainty of 4.6%. The result is consistent with theoretical calculations at next-to-next-to-leading order in perturbative QCD. The fiducial t ̄tcross-section within the experimental acceptance is also measured.©2020 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP3.1. IntroductionThe top quark is the heaviest elementary particle in the Stan-dard Model (SM), with a mass mtclose to the electroweak sym-metry breaking scale [1,2]. Studies of top-quark production and decays provide a precise probe of the SM as well as its exten-sions [3]. At the CERN Large Hadron Collider (LHC), top quarks are primarily produced in quark–antiquark pairs (t ̄t) and form an im-portant background in many searches for physics beyond the SM. Thus, a precise measurement of the t ̄tcross-section, and compar-ison with theoretical predictions of high precision, are a critical part of the LHC physics programme.A theoretical calculation of the t ̄tcross-section, σt ̄t, is available at next-to-next-to-leading order (NNLO) in quantum chromody-namics (QCD). It includes the resummation of the next-to-next-to-leading logarithmic (NNLL) soft-gluon terms [4–9] and predicts σt ̄t=832+20−29(scale)±35(PDF+αS)pb in proton–proton (pp) collisions at a centre-of-mass energy of 13 TeV, as calculated by theTop++(v2.0) program [10], using the MSTW2008 NNLO PDF set [11,12]as the central PDF set and assuming mt=172.5GeV. The scale uncertainty was determined from the envelope of pre-dictions with the QCD renormalisation and factorisation scales varied independently up or down by a factor of two. The com-bined uncertainty due to the parton distribution functions (PDFs) and the strong coupling constant, αS, was calculated following the PDF4LHC prescription [13]with the MSTW2008 NNLO, CT10 NNLO [14,15] and NNPDF2.3 5fFFN NNLO [16]PDF sets.E-mail address:atlas .publications @cern .ch.Measurements of inclusive σt ̄tat 7, 8 and 13 TeV were per-formed by both the ATLAS [17–19] and CMS [20–24] collabo-rations. All measurements are consistent with NNLO+NNLL QCD predictions. Additionally, the CMS Collaboration performed a mea-surement of σt ̄tat √s=5.02 TeV [25]. At √s=13 TeV, the ATLAS Collaboration used a data sample of 36.1 fb−1and events with an opposite-charge electron–muon pair in the final state to ob-tain σt ̄t=826.4 ±3.6(stat.)±11.5(syst.)±15.7(lumi.)±1.9(beam)pb [26], giving a total relative uncertainty of 2.4%.This Letter documents measurements of the t ̄tcross-sections in the full phase space (inclusive) and in a phase space defined to be close to the experimental measurement range (fiducial) at √s=13 TeV, using the full ppdataset collected during 2015–2018. It targets the lepton+jets t ̄tdecay mode, where one Wboson origi-nating from the top quark decays leptonically and the other Wbo-son decays hadronically, i.e.t ̄t→W+W−b ̄b→νq ̄q′b ̄b, producing a final state with one high-momentum electron or muon and four jets, two of which are b-quark-initiated jets.1A small contribution from t ̄tevents with both Wbosons decaying leptonically produc-ing the same final state due to one lepton being out of acceptance is treated as signal. A profile-likelihood fit to data in three non-overlapping regions is employed to perform the measurement.The study presented in this letter probes a final state that is complementary to the one explored in Ref. [26] and is sensitive to different t ̄tmodelling uncertainties, e.g. uncertainties related to quark jets, the understanding of which is mandatory for a large 1Events involving W→τνdecays with a subsequent decay of the τ-lepton into eνeντor μνμντare included in the signal.

Aad G., A.B. (2020). Measurement of the t ̄t production cross-section in the lepton+jets channel at √s=13 TeV with the ATLAS experiment. PHYSICS LETTERS. SECTION B, 810, 1-22 [10.1016/j.physletb.2020.135797].

Measurement of the t ̄t production cross-section in the lepton+jets channel at √s=13 TeV with the ATLAS experiment

Alberghi G. L.;Alfonsi F.;Bellagamba L.;Bindi M.;Boscherini D.;Cabras G.;Caforio D.;Carratta G.;De Castro S.;Di Sipio R.;Fabbri F.;Fabbri L.;Franchini M.;Gabrielli A.;Giacobbe B.;Lasagni Manghi F.;Macchiolo A.;Massa L.;Monzani S.;Polini A.;Rinaldi L.;Romano M.;Sbarra C.;Sbrizzi A.;Semprini-Cesari N.;Sioli M.;Todome K.;Valentinetti S.;Villa M.;Vittori C.;Vivarelli I.;Zoccoli A.;
2020

Abstract

The top anti-top quark production cross-section is measured in the lepton+jets channel using proton–proton collision data at a centre-of-mass energy of √s=13 TeV collected with the ATLAS detector at the LHC. The dataset corresponds to an integrated luminosity of 139 fb−1. Events with exactly one charged lepton and four or more jets in the final state, with at least one jet containing b-hadrons, are used to determine the t ̄tproduction cross-section through a profile-likelihood fit. The inclusive cross-section is measured to be σinc=830±0.4(stat.)±36 (syst.)±14 (lumi.) pb with a relative uncertainty of 4.6%. The result is consistent with theoretical calculations at next-to-next-to-leading order in perturbative QCD. The fiducial t ̄tcross-section within the experimental acceptance is also measured.©2020 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP3.1. IntroductionThe top quark is the heaviest elementary particle in the Stan-dard Model (SM), with a mass mtclose to the electroweak sym-metry breaking scale [1,2]. Studies of top-quark production and decays provide a precise probe of the SM as well as its exten-sions [3]. At the CERN Large Hadron Collider (LHC), top quarks are primarily produced in quark–antiquark pairs (t ̄t) and form an im-portant background in many searches for physics beyond the SM. Thus, a precise measurement of the t ̄tcross-section, and compar-ison with theoretical predictions of high precision, are a critical part of the LHC physics programme.A theoretical calculation of the t ̄tcross-section, σt ̄t, is available at next-to-next-to-leading order (NNLO) in quantum chromody-namics (QCD). It includes the resummation of the next-to-next-to-leading logarithmic (NNLL) soft-gluon terms [4–9] and predicts σt ̄t=832+20−29(scale)±35(PDF+αS)pb in proton–proton (pp) collisions at a centre-of-mass energy of 13 TeV, as calculated by theTop++(v2.0) program [10], using the MSTW2008 NNLO PDF set [11,12]as the central PDF set and assuming mt=172.5GeV. The scale uncertainty was determined from the envelope of pre-dictions with the QCD renormalisation and factorisation scales varied independently up or down by a factor of two. The com-bined uncertainty due to the parton distribution functions (PDFs) and the strong coupling constant, αS, was calculated following the PDF4LHC prescription [13]with the MSTW2008 NNLO, CT10 NNLO [14,15] and NNPDF2.3 5fFFN NNLO [16]PDF sets.E-mail address:atlas .publications @cern .ch.Measurements of inclusive σt ̄tat 7, 8 and 13 TeV were per-formed by both the ATLAS [17–19] and CMS [20–24] collabo-rations. All measurements are consistent with NNLO+NNLL QCD predictions. Additionally, the CMS Collaboration performed a mea-surement of σt ̄tat √s=5.02 TeV [25]. At √s=13 TeV, the ATLAS Collaboration used a data sample of 36.1 fb−1and events with an opposite-charge electron–muon pair in the final state to ob-tain σt ̄t=826.4 ±3.6(stat.)±11.5(syst.)±15.7(lumi.)±1.9(beam)pb [26], giving a total relative uncertainty of 2.4%.This Letter documents measurements of the t ̄tcross-sections in the full phase space (inclusive) and in a phase space defined to be close to the experimental measurement range (fiducial) at √s=13 TeV, using the full ppdataset collected during 2015–2018. It targets the lepton+jets t ̄tdecay mode, where one Wboson origi-nating from the top quark decays leptonically and the other Wbo-son decays hadronically, i.e.t ̄t→W+W−b ̄b→νq ̄q′b ̄b, producing a final state with one high-momentum electron or muon and four jets, two of which are b-quark-initiated jets.1A small contribution from t ̄tevents with both Wbosons decaying leptonically produc-ing the same final state due to one lepton being out of acceptance is treated as signal. A profile-likelihood fit to data in three non-overlapping regions is employed to perform the measurement.The study presented in this letter probes a final state that is complementary to the one explored in Ref. [26] and is sensitive to different t ̄tmodelling uncertainties, e.g. uncertainties related to quark jets, the understanding of which is mandatory for a large 1Events involving W→τνdecays with a subsequent decay of the τ-lepton into eνeντor μνμντare included in the signal.
2020
Aad G., A.B. (2020). Measurement of the t ̄t production cross-section in the lepton+jets channel at √s=13 TeV with the ATLAS experiment. PHYSICS LETTERS. SECTION B, 810, 1-22 [10.1016/j.physletb.2020.135797].
Aad G., Abbott B., Abbott D.C., Abed Abud A., Abeling K., Abhayasinghe D.K., Abidi S.H., AbouZeid O.S., Abraham N.L., Abramowicz H., Abreu H., Abulait...espandi
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