Abstract: The production of a Z boson and a photon in association with a high-mass dijet system is studied using 20.2 fb(-1) of proton-proton collision data at a centre-of-mass energy of root s = 8TeV recorded with the ATLAS detector in 2012 at the Large Hadron Collider. Final states with a photon and a Z boson decaying into a pair of either electrons, muons, or neutrinos are analysed. Electroweak and total pp -> Z gamma jj cross-sections are extracted in two fiducial regions with different sensitivities to electroweak production processes. Quartic couplings of vector bosons are studied in regions of phase space with an enhanced contribution from pure electroweak production, sensitive to vector-boson scattering processes VV -> Z gamma. No deviations from Standard Model predictions are observed and constraints are placed on anomalous couplings parameterized by higher-dimensional operators using effective field theory.

Abstract: Jet energy scale measurements and their systematic uncertainties are reported for jets measured with the ATLAS detector using proton-proton collision data with a center-of-mass energy of root s = 13 TeV, corresponding to an integrated luminosity of 3.2 fb(-1) collected during 2015 at the LHC. Jets are reconstructed from energy deposits forming topological clusters of calorimeter cells, using the anti-k(t) algorithm with radius parameter R = 0.4. Jets are calibrated with a series of simulation-based corrections and in situ techniques. In situ techniques exploit the transverse momentum balance between a jet and a reference object such as a photon, Z boson, or multijet system for jets with 20 < p(T) < 2000 GeV and pseudorapidities of vertical bar eta vertical bar < 4.5, using both data and simulation. An uncertainty in the jet energy scale of less than 1% is found in the central calorimeter region (vertical bar eta vertical bar < 1.2) for jets with 100 < p(T) < 500 GeV. An uncertainty of about 4.5% is found for low-p(T) jets with p(T) = 20 GeV in the central region, dominated by uncertainties in the corrections for multiple proton-proton interactions. The calibration of forward jets (vertical bar eta vertical bar > 0.8) is derived from dijet p(T) balance measurements. For jets of p(T) = 80 GeV, the additional uncertainty for the forward jet calibration reaches its largest value of about 2% in the range vertical bar eta vertical bar > 3.5 and in a narrow slice of 2.2 < vertical bar eta vertical bar < 2.4.

Abstract: We have chosen the reactions D-s(+) -> pi(+) pi(0)a(0)(980)(f(0)(980)) investigating the isospin violating channel D-s(+) -> pi+ pi(0)f(0)(980). The reaction was chosen because by varying the pi(0)a(0)(980)(f(0)(980)) invariant mass one goes through the peak of a triangle singularity emerging from D-s(+) -> pi(K) over bar *K, followed by (K) over bar* -> (K) over bar pi(0) and the further merging of K (K) over bar to produce the a(0)(980) or f(0)(980). We found that the amount of isospin violation had its peak precisely at the value of the pi(0)a(0)(980)(f(0)(980)) invariant mass where the singularity has its maximum, stressing the role of the triangle singularities as a factor to enhance the mixing of the f(0)(980) and a(0)(980) resonances. We calculate absolute rates for the reactions and show that they are within present measurable range. The measurement of these reactions would bring further information into the role of triangle singularities in isospin violation and the a(0) – f(0) mixing, in particular, and shed further light into the nature of the low energy scalar mesons.

Abstract: A search for the associated production of the Higgs boson with a top quark pair ((tt) over barH) is reported. The search is performed in multilepton final states using a data set corresponding to an integrated luminosity of 36.1 fb(-1) of proton-proton collision data recorded by the ATLAS experiment at a center-of-mass energy root s = 13 TeV at the Large Hadron Collider. Higgs boson decays to WW*, tau tau, and ZZ* are targeted. Seven final states, categorized by the number and flavor of charged-lepton candidates, are examined for the presence of the Standard Model Higgs boson with a mass of 125 GeVand a pair of top quarks. An excess of events over the expected background from Standard Model processes is found with an observed significance of 4.1 standard deviations, compared to an expectation of 2.8 standard deviations. The best fit for the (tt) over barH production cross section is sot (tt) over barH) = 790(-210)(+230) fb, in agreement with the Standard Model prediction of 507(-50)(+35) fb. The combination of this result with other t <overline> tH searches from the ATLAS experiment using the Higgs boson decay modes to b (b) over bar, gamma gamma and ZZ* -> 4l, has an observed significance of 4.2 standard deviations, compared to an expectation of 3.8 standard deviations. This provides evidence for the (tt) over barH production mode.

Abstract: The ratio of branching fractions R(D*(-)) = B(B-0 -> D*(-) tau(+)nu(tau))/(B-0 -> D*(-) mu(+)nu(mu)) is measured using a data sample of proton-proton collisions collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb(-1). The tau lepton is reconstructed with three charged pions in the final state. A novel method is used that exploits the different vertex topologies of signal and backgrounds to isolate samples of semitauonic decays of b hadrons with high purity. Using the B-0 -> D*(-) pi(+)pi(-)pi(+) decay as the normalization channel, the ratio B(B-0 -> D*(-) tau(+)nu(tau))/B(B-0 -> D* pi(+)pi(-)pi(+)) is measured to be 1.97 +/- 0.13 +/- 0.18, where the first uncertainty is statistical and the second systematic. An average of branching fraction measurements for the normalization channel is used to derive B(B-0 -> D*(-) tau(+)nu(tau))(_)= (1.42 +/- 0.094 +/- 0.129 +/- 0.054)%, where the third uncertainty is due to the limited knowledge of B(B-0 -> D*(-) pi(+)pi(-)pi(+)). A test of lepton flavor universality is performed using the well- measured branching fraction B(B-0 -> D*(-) mu(+)nu(mu)) to compute R(D*(-))0 = 0.291 +/- 0.019 +/- 0.026 +/- 0.013, where the third uncertainty originates from the uncertainties on B(B-0 -> D*(-) pi(+)pi(-)pi(+)) and B(B-0 -> D*(-) mu(+)nu(mu)) This measurement is in agreement with the Standard Model prediction and with previous measurements.