Georg Viehhauser

Abstract:

This Letter presents evidence for the associated production of a W boson and a top quark using 2.05 fb-1 of pp collision data at s=7TeV accumulated with the ATLAS detector at the LHC. The analysis is based on the selection of the dileptonic final states with events featuring two isolated leptons, electron or muon, with significant transverse missing momentum and at least one jet. An approach based on boosted decision trees has been developed to improve the discrimination of single top-quark Wt events from background. A template fit to the final classifier distributions is performed to determine the cross-section. The result is incompatible with the background-only hypothesis at the 3.3σ level, the expected sensitivity assuming the Standard Model production rate being 3.4σ. The corresponding cross-section is determined and found to be σWt=16.8±2.9(stat)±4.9(syst)pb, in good agreement with the Standard Model expectation. From this result the CKM matrix element |Vtb|=1.03-0.19+0.16 is derived assuming that the Wt production through |Vts| and |Vtd| is small. © 2012 CERN.

Abstract:

This Letter presents evidence for the associated production of a W boson and a top quark using 2.05 fb -1 of pp collision data at s=7TeV accumulated with the ATLAS detector at the LHC. The analysis is based on the selection of the dileptonic final states with events featuring two isolated leptons, electron or muon, with significant transverse missing momentum and at least one jet. An approach based on boosted decision trees has been developed to improve the discrimination of single top-quark Wt events from background. A template fit to the final classifier distributions is performed to determine the cross-section. The result is incompatible with the background-only hypothesis at the 3.3σ level, the expected sensitivity assuming the Standard Model production rate being 3.4σ. The corresponding cross-section is determined and found to be σ Wt =16.8±2.9(stat)±4.9(syst)pb, in good agreement with the Standard Model expectation. From this result the CKM matrix element |Vtb|=1.03-0.19+0.16 is derived assuming that the Wt production through |V ts | and |V td | is small. © 2012 CERN.

Abstract:

© 2012 CERN. Published by Elsevier B.V. A search for the Standard Model Higgs boson in proton-proton collisions with the ATLAS detector at the LHC is presented. The datasets used correspond to integrated luminosities of approximately 4.8 fb -1 collected at √s = 7 TeV in 2011 and 5.8 fb -1 at √s = 8 TeV in 2012. Individual searches in the channels H → ZZ(*) → 4l, H → γγ and H → WW(*) eνμν in the 8 TeV data are combined with previously published results of searches for H → ZZ (*) , WW (*) , bb and τ + τ - in the 7 TeV data and results from improved analyses of the H → ZZ(*) →4l and H → γγ channels in the 7 TeV data. Clear evidence for the production of a neutral boson with a measured mass of 126.0±0.4 (stat)±0.4 (sys) GeV is presented. This observation, which has a significance of 5.9 standard deviations, corresponding to a background fluctuation probability of 1.7×10 -9 , is compatible with the production and decay of the Standard Model Higgs boson.

Abstract:

A search for the Standard Model Higgs boson in the H→WW({star operator})→ℓνℓν (ℓ=e, μ) decay mode is presented. The search is performed using proton-proton collision data corresponding to an integrated luminosity of 4.7 fb-1 at a centre-of-mass energy of 7 TeV collected during 2011 with the ATLAS detector at the Large Hadron Collider. No significant excess of events over the expected background is observed. An upper bound is placed on the Higgs boson production cross section as a function of its mass. A Standard Model Higgs boson with mass in the range between 133 GeV and 261 GeV is excluded at 95% confidence level, while the expected exclusion range is from 127 GeV to 233 GeV. © 2012 CERN.