Dr Babak Abi

Abstract:

This paper presents a search for the t-channel exchange of an R-parity violating scalar top quark (t) in the e±μ∓ continuum using 2.1 fb−1 of data collected by the ATLAS detector in √s = 7 TeV pp collisions at the Large Hadron Collider. Data are found to be consistent with the expectation from the Standard Model backgrounds. Limits on R-parity-violating couplings at 95 % C.L. are calculated as a function of the scalar top mass (mt). The upper limits on the production cross section for pp→eμX, through the t-channel exchange of a scalar top quark, ranges from 170 fb for mt = 95 GeV to 30 fb for mt = 1000 GeV.

Abstract:

This Letter reports a measurement of the WW production cross section in √s=7 TeV pp collisions using data corresponding to an integrated luminosity of 1.02 fb-1 collected with the ATLAS detector. Using leptonic decays of oppositely charged W bosons, the total measured cross section is σ(pp→WW)=54.4±4.0(stat.)±3.9(syst.)±2.0(lumi.) pb, consistent with the Standard Model prediction of σ(pp→WW)=44.4±2.8 pb. Limits on anomalous electroweak triple-gauge couplings are extracted from a fit to the transverse-momentum distribution of the leading charged lepton in the event. © 2012 CERN.

Abstract:

This Letter reports a measurement of the WW production cross section in √s=7 TeV pp collisions using data corresponding to an integrated luminosity of 1.02 fb^-1 collected with the ATLAS detector. Using leptonic decays of oppositely charged W bosons, the total measured cross section is σ(pp→WW)=54.4±4.0(stat.)±3.9(syst.)±2.0(lumi.) pb, consistent with the Standard Model prediction of σ(pp→WW)=44.4±2.8 pb. Limits on anomalous electroweak triple-gauge couplings are extracted from a fit to the transverse-momentum distribution of the leading charged lepton in the event. © 2012 CERN.

Abstract:

A search for the production of single top-quarks via flavour-changing neutral-currents is presented. Data collected with the ATLAS detector at a centre-of-mass energy of √s=7 TeV, corresponding to an integrated luminosity of 2.05 fb-1, are used. Candidate events with a semileptonic top-quark decay signature are classified as signal- or background-like events by using several kinematic variables as input to a neural network. No signal is observed in the neural network output distribution and a Bayesian upper limit is placed on the production cross-section. The observed upper limit at 95% confidence level on the cross-section multiplied by the t→Wb branching fraction is measured to be σqg→t×B(t→Wb)<3.9 pb. This upper limit is converted using a model-independent approach into upper limits on the coupling strengths κugt/Λ<6.9{dot operator}10-3 TeV-1 and κcgt/Λ<1.6{dot operator}10-2 TeV-1, where Λ is the new physics scale, and on the branching fractions B(t→ug)<5.7{dot operator}10-5 and B(t→cg)<2.7{dot operator}10-4. © 2012 CERN.