Abstract: Measurements of ZZ production in the l(+)l(-)l'(+)l'(-) channel in proton-proton collisions at 13 TeV center-of-mass energy at the Large Hadron Collider are presented. The data correspond to 36.1 fb(-1) of collisions collected by the ATLAS experiment in 2015 and 2016. Here l and l ' stand for electrons or muons. Integrated and differential ZZ -> l(+)l(-)l'(+)l'(-) cross sections with Z -> l(+)l(-) candidate masses in the range of 66 GeV to 116 GeV are measured in a fiducial phase space corresponding to the detector acceptance and corrected for detector effects. The differential cross sections are presented in bins of twenty observables, including several that describe the jet activity. The integrated cross section is also extrapolated to a total phase space and to all standard model decays of Z bosons with mass between 66 GeV and 116 GeV, resulting in a value of 17.3 +/- 0.9 [+/- 0.6(start) +/- 0.5 (syst) +/- 0.6 (lumi)] pb. The measurements are found to be in good agreement with the standard model. A search for neutral triple gauge couplings is performed using the transverse momentum distribution of the leading Z boson candidate. No evidence for such couplings is found and exclusion limits are set on their parameters.

Abstract: This paper presents a study of WW gamma and WZ gamma triboson production using events from proton-proton collisions at a centre-of-mass energy of root s = 8 TeV recorded with the ATLAS detector at the LHC and corresponding to an integrated luminosity of 20.2 fb(-1). The WW gamma production cross-section is determined using a final state containing an electron, a muon, a photon, and neutrinos (e upsilon μupsilon gamma). Upper limits on the production cross-section of the e upsilon μupsilon gamma final state and theWW gamma and WZ gamma final states containing an electron or a muon, two jets, a photon, and a neutrino (e upsilon j j gamma or μupsilon j j gamma) are also derived. The results are compared to the cross-sections predicted by the Standard Model at next-to-leading order in the strong-coupling constant. In addition, upper limits on the production cross-sections are derived in a fiducial region optimised for a search for newphysics beyond the Standard Model. The results are interpreted in the context of anomalous quartic gauge couplings using an effective field theory. Confidence intervals at 95% confidence level are derived for the 14 coupling coefficients to which WW gamma and WZ gamma production are sensitive.

Abstract: A study of the decays B-s(0) -> mu(+)mu(-) and B-0 -> mu(+)mu(-) has been performed using data corresponding to an integrated luminosity of 25 fb(-1) of 7 and 8 TeV proton-proton collisions collected with the ATLAS detector during the LHC Run 1. For the B-0 dimuon decay, an upper limit on the branching fraction is set at B(B-0 -> mu(+)mu(-)) < 4.2 x 10(-10) at 95% confidence level. For B-s(0), the branching fraction B(B-s(0) -> mu(+)mu(-)) = (0.9(-0.8)(+1.1)) x 10(-9) is measured. The results are consistent with the Standard Model expectation with a p value of 4.8%, corresponding to 2.0 standard deviations.

Abstract: The inclusive production of four isolated charged leptons in pp collisions is analysed for the presence of hard double-parton scattering, using 20.2 fb(-1) of data recorded in the ATLAS detector at the LHC at centre-of-mass energy root s = 8 TeV. In the four-lepton invariant-mass range of 80 < m(4l) < 1000 GeV, an artificial neural network is used to enhance the separation between single- and double-parton scattering based on the kinematics of the four leptons in the final state. An upper limit on the fraction of events originating from double-parton scattering is determined at 95% confidence level to be f(DPS) = 0.042, which results in an estimated lower limit on the effective cross section at 95% confidence level of 1.0 mb.

Abstract: Inclusive four-jet events produced in proton-proton collisions at a centre-of mass energy of root s = 7 TeV are analysed for the presence of hard double-parton scattering using data corresponding to an integrated luminosity of 37.3 pb(-1), collected with the ATLAS detector at the LHC. The contribution of hard double-parton scattering to the production of four -jet events is extracted using an artificial neural network, assuming that hard double-parton scattering can be approximated by an uncorrelated overlaying of dijet events. For events containing at least four jets with transverse momentum PT >= 20 GeV and pseudorapidity vertical bar eta vertical bar <= 4.4, and at least one having pT >= 42.5 GeV, the contribution of hard double-parton scattering is estimated to be fDps = 0.092(-0.011)(+0.0005) (stat.) (+0.03337)(-0.011) (syst.). After combining this measurement with those of the inclusive dijet and four -jet cross -sections in the appropriate phase space regions, the effective cross-section, sigma(eff,) was determined to be sigma(eff) = 14.9(-1.0)(+1.2) (stat.) (+5.1)(-3.8) (syst.) mb. This result is consistent within the quoted uncertainties with previous measurements of sigma(eff), performed at centre-of-mass energies between 63 GeV and 8 TeV using various final states, and it corresponds to 21(-6%)(+7) of the total inelastic cross-section measured at root s = 7 TeV. The distributions of the observables sensitive to the contribution of hard double-parton scattering, corrected for detector effects, are also provided.