Faculty of Arts and Sciences
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Publication Measurement of the W-boson mass in pp collisions at s√=7TeV with the ATLAS detectorFranklin, Melissa; Huth, John; Morii, MasahiroPublication Measurement of WW/WZ→ℓνqq′ production with the hadronically decaying boson reconstructed as one or two jets in pp collisions at s√=8 TeV with ATLAS, and constraints on anomalous gauge couplingsFranklin, Melissa; Huth, John; Morii, MasahiroThis paper presents a study of the production of WW or WZ boson pairs, with one W boson decaying to eν or μν and one W or Z boson decaying hadronically. The analysis uses 20.2 fb−1 of s√=8 TeV pp collision data, collected by the ATLAS detector at the Large Hadron Collider. Cross-sections for WW/WZ production are measured in high-pT fiducial regions defined close to the experimental event selection. The cross-section is measured for the case where the hadronically decaying boson is reconstructed as two resolved jets, and the case where it is reconstructed as a single jet. The transverse momentum distribution of the hadronically decaying boson is used to search for new physics. Observations are consistent with the Standard Model predictions, and 95% confidence intervals are calculated for parameters describing anomalous triple gauge-boson couplings.Publication Search for pair production of vector-like top quarks in events with one lepton, jets, and missing transverse momentum in s√=13 TeV pp collisions with the ATLAS detectorFranklin, Melissa; Huth, John; Morii, MasahiroThe results of a search for vector-like top quarks using events with exactly one lepton, at least four jets, and large missing transverse momentum are reported. The search is optimised for pair production of vector-like top quarks in the Z(→νν)t+X decay channel. LHC pp collision data at a centre-of-mass energy of s√=13 TeV recorded by the ATLAS detector in 2015 and 2016 are used, corresponding to an integrated luminosity of 36.1 fb−1. No significant excess over the Standard Model expectation is seen and upper limits on the production cross-section of a vector-like T quark pair as a function of the T quark mass are derived. The observed (expected) 95% CL lower limits on the T mass are 870 GeV (890 GeV) for the weak-isospin singlet model, 1.05 TeV (1.06 TeV) for the weak-isospin doublet model and 1.16 TeV (1.17 TeV) for the pure Zt decay mode. Limits are also set on the mass as a function of the decay branching ratios, excluding large parts of the parameter space for masses below 1 TeV.Publication Measurement of b-hadron pair production with the ATLAS detector in proton-proton collisions at s√=8 TeVFranklin, Melissa; Huth, John; Morii, MasahiroA measurement of b-hadron pair production is presented, based on a data set corresponding to an integrated luminosity of 11.4 fb−1 of proton--proton collisions recorded at s√=8 TeV with the ATLAS detector at the LHC. Events are selected in which a b-hadron is reconstructed in a decay channel containing J/ψ→μμ, and a second b-hadron is reconstructed in a decay channel containing a muon. Results are presented in a fiducial volume defined by kinematic requirements on three muons based on those used in the analysis. The fiducial cross section is measured to be 17.7±0.1(stat.)±2.0(syst.) nb. A number of normalised differential cross sections are also measured, and compared to predictions from the Pythia8, Herwig++, MadGraph5\_aMC@NLO+Pythia8 and Sherpa event generators, providing new constraints on heavy flavour production.Publication Search for dark matter at s√=13 TeV in final states containing an energetic photon and large missing transverse momentum with the ATLAS detectorFranklin, Melissa; Huth, John; Morii, MasahiroResults of a search for physics beyond the Standard Model in events containing an energetic photon and large missing transverse momentum with the ATLAS detector at the Large Hadron Collider are reported. As the number of events observed in data, corresponding to an integrated luminosity of 36.1 fb−1 of proton-proton collisions at a centre-of-mass energy of 13 TeV, is in agreement with the Standard Model expectations, exclusion limits in models where dark-matter candidates are pair-produced are determined. For dark-matter production via an axial-vector or a vector mediator in the s-channel, this search excludes mediator masses below 750-1200 GeV for dark-matter candidate masses below 230-480 GeV at 95% confidence level, depending on the couplings. In an effective theory of dark-matter production, the limits restrict the value of the suppression scale M∗ to be above 790 GeV at 95% confidence level. A limit is also reported on the production of a high-mass scalar resonance by processes beyond the Standard Model, in which the resonance decays to Zγ and the Z boson subsequently decays into neutrinos.Publication Measurement of the k t splitting scales in Z → ℓℓ events in pp collisions at S =8 √s TeV with the ATLAS detectorFranklin, Melissa; Huth, John; Morii, MasahiroA measurement of the splitting scales occuring in the k t jet-clustering algorithm is presented for final states containing a Z boson. The measurement is done using 20.2 fb−1 of proton-proton collision data collected at a centre-of-mass energy of [Math Processing Error] TeV by the ATLAS experiment at the LHC in 2012. The measurement is based on chargedparticle track information, which is measured with excellent precision in the p T region relevant for the transition between the perturbative and the non-perturbative regimes. The data distributions are corrected for detector effects, and are found to deviate from state-of-the-art predictions in various regions of the observables.Publication Measurements of electroweak Wjj W j j production and constraints on anomalous gauge couplings with the ATLAS detectorFranklin, Melissa; Huth, John; Morii, MasahiroPublication Measurement of the t ¯ t production cross section in the τ + jets final state in p p collisions at √ s = 8 TeV using the ATLAS detector(American Physical Society (APS), 2017-04-07) Franklin, Melissa; Huth, John; Morii, MasahiroPublication Search for a new heavy gauge boson resonance decaying into a lepton and missing transverse momentum in 36 fb−1 of pp collisions at s√= 13 TeV with the ATLAS experimentFranklin, Melissa; Huth, John; Morii, MasahiroThe results of a search for new heavy W′ bosons decaying to an electron or muon and a neutrino using proton-proton collision data at a centre-of-mass energy of s√=13 TeV are presented. The dataset was collected in 2015 and 2016 by the ATLAS experiment at the Large Hadron Collider and corresponds to an integrated luminosity of 36.1 fb−1. As no excess of events above the Standard Model prediction is observed, the results are used to set upper limits on the W′ boson cross-section times branching ratio to an electron or muon and a neutrino as a function of the W′ mass. Assuming a W′ boson with the same couplings as the Standard Model W boson, W′ masses below 5.1 TeV are excluded at the 95% confidence level.Publication Search for long-lived, weakly interacting particles that decay to displaced hadronic jets in proton-proton collisions at √ s = 8 TeV with the ATLAS detectorFranklin, Melissa; Huth, John; Morii, Masahiro