This Letter presents a search for the Standard Model Higgs boson in the decay channel H→ZZ (*) →ℓ + ℓ - ℓ '+ ℓ '- , where ℓ, ℓ ' =e or μ, using proton-proton collisions at √s=7 TeV recorded with the ATLAS detector and corresponding to an integrated luminosity of 4.8 fb -1 . The four-lepton invariant mass distribution is compared with Standard Model background expectations to derive upper limits on the cross section of a Standard Model Higgs boson with a mass between 110 GeV and 600 GeV. The mass ranges 134-156 GeV, 182-233 GeV, 256-265 GeV and 268-415 GeV are excluded at the 95% confidence level. The largest upward deviations from the background-only hypothesis are observed for Higgs boson masses of 125 GeV, 244 GeV and 500 GeV with local significances of 2.1, 2.2 and 2.1 standard deviations, respectively. Once the look-elsewhere effect is considered, none of these excesses are significant. © 2012 CERN.

A search is presented for a narrow resonance decaying to a pair of Z bosons using data corresponding to 1.02fb -1 of integrated luminosity collected by the ATLAS experiment from pp collisions at √s=7TeV. Events containing either four charged leptons (ℓℓℓℓ) or two charged leptons and two jets (ℓℓjj) are analyzed and found to be consistent with the Standard Model background expectation. Lower limits on a resonance mass are set using the Randall-Sundrum (RS1) graviton model as a benchmark. Using both ℓℓℓℓ and ℓℓjj events, an RS1 graviton with k/m-pl=0.1 and mass between 325 and 845 GeV is excluded at 95% confidence level. In addition, the ℓℓℓℓ events are used to set a model-independent fiducial cross section limit of σ fid (pp→X→ZZ)<0.92pb at 95% confidence level for any new sources of ZZ production with m ZZ greater than 300 GeV. © 2012 CERN.

A measurement is presented of the cross section for the production of a W boson with one or two jets, of which at least one must be a b-jet, in pp collisions at √s = 7 TeV. Production via top decay is not included in the signal definition. The measurement is based on 35 pb-1 of data collected with the ATLAS detector at the LHC. The W + b-jet cross section is defined for jets reconstructed with the antikt clustering algorithm with transverse momentum above 25 GeV and rapidity within ±2.1. The b-jets are identified by reconstructing secondary vertices. The fiducial cross section is measured both for the electron and muon decay channel of the W boson and is found to be 10.2 ± 1.9(stat) ± 2.6(syst) pb for one lepton flavour. The results are compared with next-to-leading order QCD calculations, which predict a cross section smaller than, though consistent with, the measured value.

A combined search for the Standard Model Higgs boson with the ATLAS experiment at the LHC using datasets corresponding to integrated luminosities from 1.04 fb-1 to 4.9 fb-1 of pp collisions collected at s=7TeV is presented. The Higgs boson mass ranges 112.9-115.5 GeV, 131-238 GeV and 251-466 GeV are excluded at the 95% confidence level (CL), while the range 124-519 GeV is expected to be excluded in the absence of a signal. An excess of events is observed around mH~126GeV with a local significance of 3.5 standard deviations (σ). The local significances of H→γγ, H→ZZ(z.ast;)→ℓ+ℓ-ℓ'+ℓ'- and H→WW(z.ast;)→ℓ+νℓ'-ν- the three most sensitive channels in this mass range, are 2.8σ, 2.1σ and 1.4σ, respectively. The global probability for the background to produce such a fluctuation anywhere in the explored Higgs boson mass range 110-600 GeV is estimated to be ~1.4% or, equivalently, 2.2σ. © 2012 CERN.

A combined search for the Standard Model Higgs boson with the ATLAS experiment at the LHC using datasets corresponding to integrated luminosities from 1.04 fb-1 to 4.9 fb-1 of pp collisions collected at s=7TeV is presented. The Higgs boson mass ranges 112.9-115.5 GeV, 131-238 GeV and 251-466 GeV are excluded at the 95% confidence level (CL), while the range 124-519 GeV is expected to be excluded in the absence of a signal. An excess of events is observed around mH~126GeV with a local significance of 3.5 standard deviations (σ). The local significances of H→γγ, H→ZZ(z.ast;)→ℓ+ℓ-ℓ'+ℓ'- and H→WW(z.ast;)→ℓ+νℓ'-ν- the three most sensitive channels in this mass range, are 2.8σ, 2.1σ and 1.4σ, respectively. The global probability for the background to produce such a fluctuation anywhere in the explored Higgs boson mass range 110-600 GeV is estimated to be ~1.4% or, equivalently, 2.2σ. © 2012 CERN.