Richard Nickerson

Abstract:

A search for a heavy Standard Model Higgs boson decaying via H→ZZ→ℓ+ℓ-qq̄, where ℓ=e, μ, is presented. The search is performed using a data set of pp collisions at √s=7 TeV, corresponding to an integrated luminosity of 1.04 fb-1 collected in 2011 by the ATLAS detector at the CERN LHC collider. No significant excess of events above the estimated background is found. Upper limits at 95% confidence level on the production cross section (relative to that expected from the Standard Model) of a Higgs boson with a mass in the range between 200 and 600 GeV are derived. Within this mass range, there is at present insufficient sensitivity to exclude a Standard Model Higgs boson. For a Higgs boson with a mass of 360 GeV, where the sensitivity is maximal, the observed and expected cross section upper limits are factors of 1.7 and 2.7, respectively, larger than the Standard Model prediction. © 2011 CERN.

Abstract:

The cross section for the production of W bosons with subsequent decay W→τντ is measured with the ATLAS detector at the LHC. The analysis is based on a data sample that was recorded in 2010 at a proton-proton center-of-mass energy of s=7 TeV and corresponds to an integrated luminosity of 34 pb-1. The cross section is measured in a region of high detector acceptance and then extrapolated to the full phase space. The product of the total W production cross section and the W→τντ branching ratio is measured to be σW→τντtot=11.1±0.3(stat)±1.7(syst)±0.4(lumi) nb. © 2011 CERN.

Abstract:

A measurement is presented of the inclusive cross-section for b-jet production in association with a Z boson in pp collisions at a centre-of-mass energy of s=7 TeV. The analysis uses the data sample collected by the ATLAS experiment in 2010, corresponding to an integrated luminosity of approximately 36 pb-1. The event selection requires a Z boson decaying into high pT electrons or muons, and at least one b-jet, identified by its displaced vertex, with transverse momentum pT>25 GeV and rapidity |y|<2.1. After subtraction of background processes, the yield is extracted from the vertex mass distribution of the candidate b-jets. The ratio of this cross-section to the inclusive Z cross-section (the average number of b-jets per Z event) is also measured. Both results are found to be in good agreement with perturbative QCD predictions at next-to-leading order. © 2011 CERN.

Abstract:

The ATLAS detector at the LHC is used to search for high-mass states, such as heavy charged gauge bosons (Wʹ), decaying to a charged lepton (electron or muon) and a neutrino. Results are presented based on the analysis of pp collisions at a center-of-mass energy of 7 TeV corresponding to an integrated luminosity of 4.7 fb−1. No excess beyond Standard Model expectations is observed. AWʹ with Sequential Standard Model couplings is excluded at the 95% credibility level for masses up to 2.55 TeV. Excited chiral bosons (W*) with equivalent coupling strength are excluded for masses up to 2.42 TeV.