Abstract: A technique is presented to measure the efficiency with which c-jets are mistagged as b-jets (mistagging efficiency) using t (t) over bar events, where one of theW bosons decays into an electron or muon and a neutrino and the other decays into a quark-antiquark pair. The measurement utilises the relatively large and known W -> cs branching ratio, which allows ameasurement to be made in an inclusive c-jet sample. The data sample used was collected by the ATLAS detector at root s = 13 TeV and corresponds to an integrated luminosity of 139 fb(-1). Events are reconstructed using a kinematic likelihood technique which selects the mapping between jets and t (t) over bar decay products that yields the highest likelihood value. The distribution of the b-tagging discriminant for jets from the hadronic W decays in data is compared with that in simulation to extract the mistagging efficiency as a function of jet transverse momentum. The total uncertainties are in the range 3-17%. The measurements generally agree with those in simulation but there are some differences in the region corresponding to the most stringent b-jet tagging requirement.

Abstract: A measurement of the energy asymmetry in jet-associated top-quark pair production is presented using 139 fb(-1) of data collected by the ATLAS detector at the Large Hadron Collider during pp collisions at root s = 13 TeV. The observable measures the different probability of top and antitop quarks to have the higher energy as a function of the jet scattering angle with respect to the beam axis. The energy asymmetry is measured in the semileptonic t (t) over bar decay channel, and the hadronically decaying top quark must have transverse momentum above 350 GeV. The results are corrected for detector effects to particle level in three bins of the scattering angle of the associated jet. The measurement agrees with the SM prediction at next-to-leading-order accuracy in quantum chromodynamics in all three bins. In the bin with the largest expected asymmetry, where the jet is emitted perpendicular to the beam, the energy asymmetry is measured to be -0.043 +/- 0.020, in agreement with the SM prediction of -0.037 +/- 0.003. Interpreting this result in the framework of the Standard Model effective field theory (SMEFT), it is shown that the energy asymmetry is sensitive to the top-quark chirality in four-quark operators and is therefore a valuable new observable in global SMEFT fits.

Abstract: The inclusive Higgs boson production cross-section is measured in the di-photon and the ZZ -> 4l decay channels using 31.4 and 29.0 fb-1 of pp collision data respectively, collected with the ATLAS detector at a centre-of-mass energy of <mml:msqrt>s</mml:msqrt>=13.6 TeV. To reduce the model dependence, the measurement in each channel is restricted to a particle-level phase space that closely matches the channel's detector-level kinematic selection, and it is corrected for detector effects. These measured fiducial cross-sections are sigma fid,gamma gamma= 76-13+14</mml:msubsup> fb, and sigma fid,4l= 2.80<mml:mspace width=“0.166667em”></mml:mspace>+/- <mml:mspace width=“0.166667em”></mml:mspace>0.74 fb, in agreement with the corresponding Standard Model predictions of 67.6 +/- 3.7 fb and 3.67 +/- 0.19 fb. Assuming Standard Model acceptances and branching fractions for the two channels, the fiducial measurements are extrapolated to the full phase space yielding total cross-sections of sigma (pp -> H)=67-11+12 pb and 46 +/- 12 pb at 13.6 TeV from the di-photon and ZZ -> 4l measurements respectively. The two measurements are combined into a total cross-section measurement of sigma (pp -> H)=58.2 +/- 8.7 pb, to be compared with the Standard Model prediction of sigma <mml:msub>(pp -> H)SM=59.9 +/- 2.6 pb.