Abstract: A search for the leptonic charge asymmetry (A(c)(l)) of top-quark-antiquark pair production in association with a W boson (t (t) over barW) is presented. The search is performed using final states with exactly three charged light leptons (electrons or muons) and is based on root s = 13TeV proton-proton collision data collected with the ATLAS detector at the Large Hadron Collider at CERN during the years 2015-2018, corresponding to an integrated luminosity of 139 fb(-1). A profile-likelihood fit to the event yields in multiple regions corresponding to positive and negative differences between the pseudorapidities of the charged leptons from top-quark and top-antiquark decays is used to extract the charge asymmetry. At reconstruction level, the asymmetry is found to be -0.12 +/- 0.14 (stat.) +/- 0.05 (syst.). An unfolding procedure is applied to convert the result at reconstruction level into a charge-asymmetry value in a fiducial volume at particle level with the result of -0.11 +/- 0.17 (stat.) +/- 0.05 (syst.). The Standard Model expectations for these two observables are calculated using Monte Carlo simulations with next-to-leading-order plus parton shower precision in quantum chromodynamics and including next-to-leading-order electroweak corrections. They are -0.084(-0.003)(+0.005) (scale) +/- 0.006 (MC stat.) and -0.063(-0.004)(+0.007) (scale) +/- 0.004 (MC stat.) respectively, and in agreement with the measurements.

Abstract: A search for pair-produced vector-like quarks using events with exactly one lepton (e or mu), at least four jets including at least one b-tagged jet, and large missing transverse momentum is presented. Data from proton-proton collisions at a centre-of-mass energy of root s =13 TeV, recorded by the ATLAS detector at the LHC from 2015 to 2018 and corresponding to an integrated luminosity of 139 fb(-1), are analysed. Vector-like partners T and B of the top and bottom quarks are considered, as is a vector-like X with charge +5/3, assuming their decay into a W, Z, or Higgs boson and a third-generation quark. No significant deviations from the Standard Model expectation are observed. Upper limits on the production cross-section of T and B quark pairs as a function of their mass are derived for various decay branching ratio scenarios. The strongest lower limits on the masses are 1.59 TeV assuming mass-degenerate vector-like quarks and branching ratios corresponding to the weak-isospin doublet model, and 1.47 TeV (1.46 TeV) for exclusive T -> Zt (B/X -> Wt) decays. In addition, lower limits on the T and B quark masses are derived for all possible branching ratios.

Abstract: The very rare D*(2007)(0) -> mu(+) mu(-) decay is searched for by analysing B- -> pi (-) mu(+) mu(-) decays. The analysis uses a sample of beautymesons produced in protonproton collisions collected with the LHCb detector between 2011 and 2018, corresponding to an integrated luminosity of 9 fb(-1). The signal signature corresponds to simultaneous peaks in the mu(+) mu(-) and pi(-) mu(+) mu(-) invariant masses. No evidence for an excess of events over background is observed and an upper limit is set on the branching fraction of the decay at B(D-*(2007)(0) -> mu(+) mu(-)) < 2.6 x 10(-8) at 90% confidence level. This is the first limit on the branching fraction of D*(2007)(0) -> mu(+) mu(-) decays and the most stringent limit on D* (2007)(0) decays to leptonic final states. The analysis is the first search for a rare charm-meson decay exploiting production via beauty decays.

Abstract: Measurements of differential cross sections are presented for inclusive isolated photon production in pp collisions at a centre-of-mass energy of 13TeV provided by the LHC and using 139 fb(-1) of data recorded by the ATLAS experiment. The cross sections are measured as functions of the photon transverse energy in different regions of photon pseudorapidity. The photons are required to be isolated by means of a fixed-cone method with two different cone radii. The dependence of the inclusive-photon production on the photon isolation is investigated by measuring the fiducial cross sections as functions of the isolation-cone radius and the ratios of the differential cross sections with different radii in different regions of photon pseudorapidity. The results presented in this paper constitute an improvement with respect to those published by ATLAS earlier: the measurements are provided for different isolation radii and with a more granular segmentation in photon pseudorapidity that can be exploited in improving the determination of the proton parton distribution functions. These improvements provide a more in-depth test of the theoretical predictions. Next-to-leading-order QCD predictions from JETPHOX and SHERPA and next-to-next-to-leading-order QCD predictions from NNLOJET are compared to the measurements, using several parameterisations of the proton parton distribution functions. The measured cross sections are well described by the fixed-order QCD predictions within the experimental and theoretical uncertainties in most of the investigated phase-space region.

Abstract: Using a proton-proton collision data sample collected by the LHCb detector and corresponding to an integrated luminosity of 5.7 fb(-1), the lifetime of the light B-s(0) mass eigenstate, tau(L), is measured using the B-s(0) -> J/psi eta decay mode to be tau(L) = 1.445 +/- 0.016(stat) +/- 0.008(syst) ps. A combination of this result with a previous LHCb analysis using an independent dataset corresponding to 3 fb(-1) of integrated luminosity gives tau(L) = 1.452 +/- 0.014 +/- 0.007 +/- 0.002 ps, where the first uncertainty is statistical, the second due to the uncorrelated part of the systematic uncertainty and the third due to the correlated part of the systematic uncertainty.