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10.1140-epjc-s10052-016-4501-2.pdf (1.61 MB)

Addendum to ‘measurement of the tt¯ production cross-section using eµ events with b-tagged jets in pp collisions at vs= 7 and 8 TeV with the ATLAS detector’

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posted on 2023-06-09, 06:07 authored by Benedict AllbrookeBenedict Allbrooke, Lily AsquithLily Asquith, Alessandro CerriAlessandro Cerri, C A Chavez Barajas, Antonella De SantoAntonella De Santo, Fabrizio SalvatoreFabrizio Salvatore, I Santoyo Castillo, K Suruliz, Mark SuttonMark Sutton, Iacopo Vivarelli, The ATLAS Collaboration
The ATLAS measurement of the inclusive top quark pair (tt¯) cross-section stt¯ in proton–proton collisions at vs=8 TeV has been updated using the final 2012 luminosity calibration. The updated cross-section result is: stt¯=242.9±1.7±5.5±5.1±4.2pb, where the four uncertainties arise from data statistics, experimental and theoretical systematic effects, knowledge of the integrated luminosity and of the LHC beam energy. The result is consistent with theoretical QCD calculations at next-to-next-to-leading order. The measurement of the ratio of tt¯ cross-sections at vs=8 TeV and vs=7 TeV, and the vs=8 TeV fiducial measurement corresponding to the experimental acceptance of the leptons, have also been updated. The most precise measurement of the tt¯ cross-section (stt¯) in proton–proton collisions at vs=8 TeV from the ATLAS Collaboration was made using events with an opposite-charge electron–muon pair and one or two b-tagged jets [1], and used a preliminary calibration of the integrated luminosity. The luminosity calibration has been finalised since [2] with a total uncertainty of 1.9%, corresponding to a substantial improvement on the previous uncertainty of 2.8%. Since the uncertainty on the integrated luminosity contributed 3.1% of the total 4.3% uncertainty on the stt¯ measurement reported in [1], a significant improvement in the measurement is possible by using the new luminosity calibration, as documented in this Addendum. The new calibration corresponds to an integrated luminosity of 20.2 fb-¹ for the vs=8 TeV sample, a decrease of 0.2%. The cross-section was recomputed taking into account the effects on both the conversion of the tt¯ event yield to a cross-section, and the background estimates, giving a result of: stt¯=242.9±1.7±5.5±5.1±4.2pb, where the four uncertainties arise from data statistics, experimental and theoretical systematic effects, knowledge of the integrated luminosity, and of the LHC beam energy, giving a total uncertainty of 8.8 pb (3.6 %). The result is consistent with the theoretical prediction of 252.9-14.5+13.3 pb, calculated at next-to-next-to-leading-order with next-to-next-to-leading-logarithmic soft gluon terms with the top++ 2.0 program [3] as discussed in detail in Ref. [1]. The updated value of the ratio of cross-sections Rtt¯=stt¯(8 TeV)/stt¯(7 TeV) is: Rtt¯=1.328±0.024±0.015±0.038±0.001, with uncertainties defined as above, adding in quadrature to a total of 0.047. The largest uncertainty comes from the uncertainties on the integrated luminosities, considered to be uncorrelated between the vs=7 TeV and vs=8 TeV datasets. This result is 2.1s below the expectation of 1.430±0.013 calculated from top++ 2.0 as discussed in Ref. [1]. The updated fiducial cross-sections, for a tt¯ decay producing an eµ pair within a given fiducial region, are shown in Table 1, updating Table 5 of Ref. [1]. The results are given both for the analysis requirements of pT>25GeV and |?|<2.5 for both leptons, and for a reduced acceptance of pT>30GeV and |?|<2.4. They are given separately for the two cases where events with either one or both leptons coming from t?W?t?l rather than the direct decay t?W?l(l=e or µ) are included, or where the contributions involving t decays are subtracted. The results shown for the vs=7 TeV data sample are unchanged with respect to those in Ref. [1]. The results for the top quark pole mass and limits on light supersymmetric top squarks presented in Ref. [1] are derived from vs=7 TeV and vs=8 TeV cross-section measurements taken together, and would be only slightly improved by the luminosity update described here.




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European Physical Journal C: Particles and Fields




Springer Verlag





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