Differential $t\bar{t}$ cross-section measurements using boosted top quarks in the all-hadronic final state with 139 fb${}^{-1}$ of ATLAS data

Abstract

Measurements of single-, double-, and triple-differential cross-sections are presented for boosted top-quark pair-production in 13 $\text{TeV}$ proton-proton collisions recorded by the ATLAS detector at the LHC. The top quarks are observed through their hadronic decay and reconstructed as large-radius jets with the leading jet having transverse momentum ($p_{\text{T}}$) greater than 500 GeV. The observed data are unfolded to remove detector effects. The particle-level cross-section, multiplied by the $t\bar{t}\to WWb\bar{b}$ branching fraction and measured in a fiducial phase space defined by requiring the leading and second-leading jets to have $p_{\text{T}}>500$ GeV and $p_{\text{T}}>350$ GeV, respectively, is $331\pm 3\text{(stat.)}\pm 39\text{(syst.)}$ fb. This is approximately 20$\%$ lower than the prediction of $398_{-49}^{+48}$ fb by Powheg+Pythia 8 with next-to-leading-order (NLO) accuracy but consistent within the theoretical uncertainties. Results are also presented at the parton level, where the effects of top-quark decay, parton showering, and hadronization are removed such that they can be compared with fixed-order next-to-next-to-leading-order (NNLO) calculations. The parton-level cross-section, measured in a fiducial phase space similar to that at particle level, is $1.94\pm 0.02\text{(stat.)}\pm 0.25\text{(syst.)}$ pb. This agrees with the NNLO prediction of $1.96_{-0.17}^{+0.02}$ pb. Reasonable agreement with the differential cross-sections is found for most NLO models, while the NNLO calculations are generally in better agreement with the data. The differential cross-sections are interpreted using a Standard Model effective field-theory formalism and limits are set on Wilson coefficients of several four-fermion operators.

105 pages in total, author list starting page 88, 50 figures, 5 tables, published in JHEP. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/TOPQ-2018-11

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