Measurement of differential cross sections in $t\bar t$ and $t\bar t+$jets production in the lepton+jets decay mode in $pp$ collisions at $\sqrt s=$ 13 TeV using 140 fb$^{-1}$ of ATLAS data

Differential cross sections for top-quark pair production, inclusively and in association with jets, are measured in $pp$ collisions at a centre-of-mass energy of 13 TeV with the ATLAS detector at the LHC using an integrated luminosity of 140 fb$^{-1}$. The events are selected with one charged lepton (electron or muon) and at least four jets. The differential cross sections are presented at particle level as functions of several jet observables, including angular correlations, jet transverse momenta and invariant masses of the jets in the final state, which characterize the kinematics and dynamics of the top-antitop system and the hard QCD radiation in the system with associated jets. The typical precision is $(5-15)\%$ for the absolute differential cross sections and $(2-4)\%$ for the normalised differential cross sections. Next-to-leading-order and next-to-next-to-leading-order QCD predictions are found to provide in general an adequate description of the rate and shape of the jet-angular observables. The description of the transverse momentum and invariant mass observables is improved when next-to-next-to-leading-order QCD corrections are included.