Measurement of jet activity in top quark events using the $e\mu$ final state with two $b$-tagged jets in $pp$ collisions at $\sqrt{s}=8$ TeV with the ATLAS detector

Abstract

Measurements of the jet activity in $t\bar{t}$ events produced in proton--proton collisions at $\sqrt{s}=8$ TeV are presented, using $20.3$fb${}^{-1}$ of data collected by the ATLAS experiment at the Large Hadron Collider. The events were selected in the dilepton $e\mu$ decay channel with two identified $b$-jets. The numbers of additional jets for various jet transverse momentum ($p_T$) thresholds, and the normalised differential cross-sections as a function of $p_T$ for the five highest-$p_T$ additional jets, were measured in the jet pseudorapidity range $|\eta |<4.5$. The gap fraction, the fraction of events which do not contain an additional jet in a central rapidity region, was measured for several rapidity intervals as a function of the minimum $p_T$ of a single jet or the scalar sum of $p_T$ of all additional jets. These fractions were also measured in different regions of the invariant mass of the $e\mu b\bar{b}$ system. All measurements were corrected for detector effects, and found to be mostly well-described by predictions from next-to-leading-order and leading-order $t\bar{t}$ event generators with appropriate parameter choices. The results can be used to further optimise the parameters used in such generators.

42 pages plus author list + cover pages (49 pages total), 19 figures, 11 tables, published in JHEP. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/TOPQ-2015-04/

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• Off-shell Top Quarks with One Jet at the LHC: A comprehensive analysis at NLO QCD
• Measurement of normalized differential $\mathrm{t}\overline{\mathrm{t}}$ cross sections in the dilepton channel from pp collisions at $\sqrt{s}=$ 13 TeV
• Measurement of lepton differential distributions and the top quark mass in $t\bar{t}$ production in $pp$ collisions at $\sqrt{s}=8$ TeV with the ATLAS detector
• Top-Quark Physics: Status and Prospects
• Measurements of differential cross sections of top quark pair production in association with jets in $pp$ collisions at $\sqrt{s}=13$ TeV using the ATLAS detector
• Direct top-quark decay width measurement in the $t\bar{t}$ lepton+jets channel at $\sqrt{s}$=8 TeV with the ATLAS experiment
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