Georg Viehhauser

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 inner detector is used to reconstruct secondary vertices due to hadronic interactions of primary collision products, so probing the location and amount of material in the inner region of ATLAS. Data collected in 7 TeV pp collisions at the LHC, with a minimum bias trigger, are used for comparisons with simulated events. The reconstructed secondary vertices have spatial resolutions ranging from ∼ 200μm to 1 mm. The overall material description in the simulation is validated to within an experimental uncertainty of about 7%. This will lead to a better understanding of the reconstruction of various objects such as tracks, leptons, jets, and missing transverse momentum. © 2012 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.