Cigdem Issever

Abstract:

We report a measurement of the cross section of single top-quark production in the t-channel using 1.04 fb-1 of pp collision data at s=7 TeV recorded with the ATLAS detector at the LHC. Selected events feature one electron or muon, missing transverse momentum, and two or three jets, exactly one of them identified as originating from a b quark. The cross section is measured by fitting the distribution of a multivariate discriminant constructed with a neural network, yielding σt=83±4(stat.)-19 +20(syst.) pb, which is in good agreement with the prediction of the Standard Model. Using the ratio of the measured to the theoretically predicted cross section and assuming that the top-quark-related CKM matrix elements obey the relation |Vtb|≫|Vts|, |Vtd|, the coupling strength at the W-t-b vertex is determined to be |Vtb|=1.13-0.13 +0.14. If it is assumed that |Vtb|≤1 a lower limit of |Vtb|>0.75 is obtained at the 95% confidence level. © 2012 CERN.

Abstract:

This Letter presents measurements of l±νγ and l+l-γ (l=e, μ) production in 1.02fb-1 of pp collision data recorded at s=7TeV with the ATLAS detector at the LHC in the first half of 2011. Events dominated by Wγ and Zγ production with leptonic decays of the W and Z bosons are selected, and their production cross sections and kinematic properties are measured in several ranges of the photon transverse energy. The results are compared to Standard Model predictions and are used to determine limits on anomalous WWγ and ZZγ/Zγγ couplings. © 2012 CERN.

Abstract:

A measurement of the cross section of top quark pair production in proton-proton collisions recorded with the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy of 7 TeV is reported. The data sample used corresponds to an integrated luminosity of 2.05 fb-1. Events with an isolated electron or muon and a τ lepton decaying hadronically are used. In addition, a large missing transverse momentum and two or more energetic jets are required. At least one of the jets must be identified as originating from a b quark. The measured cross section, σtt-=186±13(stat.)±20(syst.)±7(lumi.) pb, is in good agreement with the Standard Model prediction. © 2012 CERN.

Abstract:

A search for a heavy Standard Model Higgs boson decaying via H→ZZ→ℓ+ℓ-qq̄, where ℓ=e or μ, is presented. The search uses a data set of pp collisions at s=7TeV, corresponding to an integrated luminosity of 4.7fb-1 collected in 2011 by the ATLAS detector at the CERN LHC. No significant excess of events above the estimated background is found. Upper limits at 95% confidence level on the production cross section of a Higgs boson with a mass in the range between 200 and 600GeV are derived. A Standard Model Higgs boson with a mass in the range 300GeV≤mH≤322GeV or 353GeV≤mH≤410GeV is excluded at 95% CL. The corresponding expected exclusion range is 351GeV≤mH≤404GeV at 95% CL. © 2012 CERN.

Abstract:

A search for a Standard Model Higgs boson decaying via H→ZZ→ℓ+ℓ-νν-, where ℓ represents electrons or muons, is presented. It is based on proton-proton collision data at s=7TeV, collected by the ATLAS experiment at the LHC during 2011 and corresponding to an integrated luminosity of 4.7fb-1. The data agree with the expected Standard Model backgrounds. Upper limits on the Higgs boson production cross section are derived for Higgs boson masses between 200 GeV and 600 GeV and the production of a Standard Model Higgs boson with a mass in the range 319-558 GeV is excluded at the 95% confidence level. © 2012 CERN.