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Alexander, G.

Publications and source records attributed to Alexander, G..

At least 577 records · Page 32
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DOE OSTI2012

Measurement of τ polarization in W→τν decays with the ATLAS detector in pp collisions at $\sqrt{s} =7~\mathrm{TeV}$

Here in this paper, a measurement of τ polarization in W→τν decays is presented. It is measured from the energies of the decay products in hadronic τ decays with a single final state charged particle. The data, corresponding to an integrated luminosity of 24 pb -1 , were collected by the ATLAS experiment at the Large Hadron Collider in 2010. The measured value of the τ polarization is P τ = -1.06 ± 0.04 (stat)$+0.05\atop{-0.07}$ (syst), in agreement with the Standard Model prediction, and is consistent with a physically allowed 95 % CL interval [-1,-0.91]. Measurements of τ polarization have not previously been made at hadron colliders.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

Measurement of $t\bar{t}$ production with a veto on additional central jet activity in pp collisions at $\sqrt{s}=7$ TeV using the ATLAS detector

A measurement of the jet activity in $t\bar{t}$ events produced in proton–proton collisions at a centre-of-mass energy of 7 TeV is presented, using 2.05 fb -1 of integrated luminosity collected by the ATLAS detector at the Large Hadron Collider. The $t\bar{t}$ events are selected in the dilepton decay channel with two identified b-jets from the top quark decays. Events are vetoed if they contain an additional jet with transverse momentum above a threshold in a central rapidity interval. The fraction of events surviving the jet veto is presented as a function of this threshold for four different central rapidity interval definitions. An alternate measurement is also performed, in which events are vetoed if the scalar transverse momentum sum of the additional jets in each rapidity interval is above a threshold. In both measurements, the data are corrected for detector effects and compared to the theoretical models implemented in MC@NLO, Powheg, Alpgen and Sherpa. The experimental uncertainties are often smaller than the spread of theoretical predictions, allowing deviations between data and theory to be observed in some regions of phase space.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

Measurement of the top quark mass with the template method in the $t\bar{t} \to\mathrm{lepton}+\mathrm{jets}$ channel using ATLAS data

The top quark mass has been measured using the template method in the $t\bar{t} →lepton + jets channel based on data recorded in 2011 with the ATLAS detector at the LHC. The data were taken at a proton-proton centre-of-mass energy of √s = 7 TeV and correspond to an integrated luminosity of 1.04 fb -1 . The analyses in the e + jets and μ + jets decay channels yield consistent results. Here the top quark mass is measured to be m top = 174.5±0.6 stat ±2.3 syst GeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

Measurement of the charge asymmetry in top quark pair production in pp collisions at $\sqrt{s}=7\ \mathrm{TeV}$ using the ATLAS detector

A measurement of the top-antitop production charge asymmetry A C is presented using data corresponding to an integrated luminosity of 1.04 fb -1 of pp collisions at √s = 7 TeV collected by the ATLAS detector at the LHC. Events are selected with a single lepton (electron or muon), missing transverse momentum and at least four jets of which at least one jet is identified as coming from a b-quark. A kinematic fit is used to reconstruct the tt event topology. After background subtraction, a Bayesian unfolding procedure is performed to correct for acceptance and detector effects. The measured value of A C is A C =-0.019±0.028 (stat.)±0.024 (syst.), consistent with the prediction from the MC@NLO Monte Carlo generator of A C = 0.006±0.002. Measurements of A C in two ranges of invariant mass of the top-antitop pair are also shown.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

Search for lepton flavour violation in the eμ continuum with the ATLAS detector in $\sqrt{s} = 7~\mbox{TeV}$ pp collisions at the LHC

This paper presents a search for the t-channel exchange of an R-parity violating scalar top quark ($\sim\atop{t}$) 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 (m$_t^-$). 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 m$_t^-$ = 95 GeV to 30 fb for m$_t^-$ = 1000 GeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗