Professor Claire Gwenlan

Abstract:

A search for resonances produced in 7 TeV proton-proton collisions and decaying into top-quark pairs is described. In this Letter events where the top-quark decay produces two massive jets with large transverse momenta recorded with the ATLAS detector at the Large Hadron Collider are considered. Two techniques that rely on jet substructure are used to separate top-quark jets from those arising from light quarks and gluons. In addition, each massive jet is required to have evidence of an associated bottom-quark decay. The data are consistent with the Standard Model, and limits can be set on the production cross section times branching fraction of a Z′ boson and a Kaluza-Klein gluon resonance. These limits exclude, at the 95% credibility level, Z′ bosons with masses 0.70-1.00 TeV as well as 1.28-1.32 TeV and Kaluza-Klein gluons with masses 0.70-1.62 TeV. © 2013 Cern for the benefit of the ATLAS collaboration.

Abstract:

A measurement of the Λb0 lifetime and mass in the decay channel Λb0→J/ψ(μ+μ-)Λ0(pπ -) is presented. The analysis uses a signal sample of about 2200 Λb0 and Λ̄b0 decays that are reconstructed in 4.9 fb -1 of ATLAS pp collision data collected in 2011 at the LHC center-of-mass energy of 7 TeV. A simultaneous mass and decay time maximum likelihood fit is used to extract the Λb0 lifetime and mass. They are measured to be τΛb=1.449±0.036(stat) ±0.017(syst) ps and mΛb=5619.7±0. 7(stat)±1.1(syst) MeV.

Abstract:

A search for squarks and gluinos in final states containing jets, missing transverse momentum and no high-pT electrons or muons is presented. The data represent the complete sample recorded in 2011 by the ATLAS experiment in 7 TeV proton-proton collisions at the Large Hadron Collider, with a total integrated luminosity of 4.7 fb-1. No excess above the Standard Model background expectation is observed. Gluino masses below 860 GeV and squark masses below 1320 GeV are excluded at the 95% confidence level in simplified models containing only squarks of the first two generations, a gluino octet and a massless neutralino, for squark or gluino masses below 2 TeV, respectively. Squarks and gluinos with equal masses below 1410 GeV are excluded. In minimal supergravity/constrained minimal supersymmetric Standard Model models with tanâ-¡β=10, A0=0 and μ>0, squarks and gluinos of equal mass are excluded for masses below 1360 GeV. Constraints are also placed on the parameter space of supersymmetric models with compressed spectra. These limits considerably extend the region of supersymmetric parameter space excluded by previous measurements with the ATLAS detector.

Abstract:

The production of the excited charm mesons D 1(2420) and D2*(2460) in ep collisions has been measured with the ZEUS detector at HERA using an integrated luminosity of 373pb -1. The masses of the neutral and charged states, the widths of the neutral states, and the helicity parameter of D 1(2420) 0 were determined and compared with other measurements and with theoretical expectations. The measured helicity parameter of the D10 allows for some mixing of S- and D-waves in its decay to D *±π Π. The result is also consistent with a pure D-wave decay. Ratios of branching fractions of the two decay modes of the D2*(2460)0 and D2*(2460)± states were measured and compared with previous measurements. The fractions of charm quarks hadronising into D 1 and D2* were measured and are consistent with those obtained in e +e - annihilations. © 2012 Elsevier B.V.

Abstract:

Measurements are presented of differential crosss√ ections for top quark pair production in pp collisions at s = 7 TeV relative to the total inclusive top quark pair production cross-section. A data sample of 2.05 fb−1 recorded by the ATLAS detector at the Large Hadron Collider is used. Relative differential cross-sections are derived as a function of the invariant mass, the transverse momentum and the rapidity of the top quark pair system. Events are selected in the lepton (electron or muon) + jets channel. The backgroundsubtracted differential distributions are corrected for detector effects, normalized to the total inclusive top quark pair production cross-section and compared to theoretical predictions. The measurement uncertainties range typically between 10 % and 20 % and are generally dominated by systematic effects. No significant deviations from the Standard Model expectations are observed.