Abstract
Measurements are made of differential cross-sections of highly boosted pair-produced top quarks as a function of top-quark and $t\bar{t}$ system kinematic observables using proton--proton collisions at a center-of-mass energy of $\sqrt{s} = 13$ TeV. The data set corresponds to an integrated luminosity of $36.1$ fb$^{-1}$, recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. Events with two large-radius jets in the final state, one with transverse momentum $p_{\rm T} > 500$ GeV and a second with $p_{\rm T}>350$ GeV, are used for the measurement. The top-quark candidates are separated from the multijet background using jet substructure information and association with a $b$-tagged jet. The measured spectra are corrected for detector effects to a particle-level fiducial phase space and a parton-level limited phase space, and are compared to several Monte Carlo simulations by means of calculated $\chi^2$ values. The cross-section for $t\bar{t}$ production in the fiducial phase-space region is $292 \pm 7 \ \rm{(stat)} \pm 76 \rm{(syst)}$ fb, to be compared to the theoretical prediction of $384 \pm 36$ fb.
Highlights
The large top-quark pair-production cross-section at the Large Hadron Collider (LHC) allows detailed studies of the characteristics of the production of top-antitop quark pairs, providing an opportunity to further test the Standard Model (SM)
The previous measurements and these results provide a coherent picture that the current NLO Monte Carlo models for tt production and decay overestimate the production of highly boosted top quarks
Measurements of differential cross-sections of highly boosted pair-produced top quarks in 13 TeV pp collisions are presented in a data sample of 36.1 fb−1 collected by the ATLAS detector at the LHC
Summary
The large top-quark pair-production cross-section at the Large Hadron Collider (LHC) allows detailed studies of the characteristics of the production of top-antitop (tt) quark pairs, providing an opportunity to further test the Standard Model (SM). Measurements of partonlevel differential cross-sections are presented, where the detector-level distributions are unfolded to the top quark at the parton-level in a limited phase-space region These allow comparisons to the higher-order calculations that are currently restricted to stable top quarks [1,2,3]. These differential cross-sections are similar to those studied in dijet measurements at large jet transverse momentum [23,24] and are sensitive to effects of initialand final-state radiation (ISR and FSR), to different parton distribution functions (PDF) and to different schemes for matching matrix-element calculations to parton shower models.
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