Session E9: Physics of the Top Quark I

Single-Top Quark Search Results with Early ATLAS Data

We present the first studies using ATLAS data to investigate the single-top quark t-channel production at the LHC. The data were collected from proton-proton collisions occurring at 7 TeV center-of-mass energy. Selections based on the kinematical signature of the single-top quark process in simulated events are used to isolate the signal while removing background events in data. To distinguish this process from others such as the $t\bar{t}$ process, W+jets and QCD, we require an energetic final state including two jets, one of which must be tagged as a b-jet, one lepton, and missing energy. We report the results of this preliminary study and discuss the implications for future analyses.   

Measurement of single top quark production cross section at CDF

We report a measurement of the single top quark production cross section based on 6.4/fb of data collected by the CDF experiment at the Fermilab Tevatron. The signal is separated from the background using a Bayesian Neural Network. The CKM matrix element value $\vert $Vtb$\vert $ will be extracted from this measurement.   

Single Top Quark Production at D0 Using Boosted Decision Trees

We present improved cross section measurements of single top quarks with the D0 experiment at the Fermilab Tevatron. The measurements have been performed using Boosted Decision Trees with 5.4 fb$^{-1}$ of data.   

Measurement of the Single Top Quark Production Cross Sections at D0

We present new measurements of s-channel and t-channel production cross sections for single top quarks at the D0 experiment using 5.4 fb$^{-1}$ of data from Fermilab's proton-antiproton Tevatron collider.   

Measurement of CP Violation In Single Top Production

We present the study of CP violation in single top quark production at the D0 experiment at the Fermilab Tevatron. CP violation in the top electroweak interaction results in different single top quark production cross sections for top and antitop quarks. We consider the asymmetry in the total number of leptons ($\ell^+$ and $\ell^-$) in the final state. We perform the search separately in the electron+jets and muon+jets final states using 5.4 fb$^{-1}$ of data.   

Measurement of the top quark pair production cross section in pp collisions at 7 TeV center of mass energy using secondary vertex b-tagging

We present a measurement of top quark pair production cross section using 36 pb$^{-1}$ of data collected by the CMS detector in $pp$ collisions at a center-of-mass energy of 7 TeV. We select events containing one isolated muon, high missing transverse energy and at least three energetic jets. After using a data driven method to estimate the amount of QCD in our preselected data, further separation of the signal from the W boson background was attained through the identification of the $b$-jets in the events by reconstructing secondary vertices. The cross section is extracted from the excess of tagged events with at least three jets over the background prediction.   

Measurement of the top quark pair production cross section in $pp$ collisions at 7 TeV center of mass energy using electrns, jets and $b$-tags

We present a measurement of top quark pair production cross section using 36 pb$^{-1}$ of data collected by the CMS detector in pp collisions at a center-of-mass energy of 7~TeV. We select events containing one isolated electron, high missing transverse energy and at least three energetic jets. Data driven methods are used to estimate the amount of QCD and $W+$jets in our preselected data, and these backgrounds are then suppressed through the identification of the $b$-jets by reconstructing secondary vertices. The cross section is extracted from the excess of tagged events with at least three jets over the background prediction.   

Measurement of the top quark pair production cross section with early ATLAS data

We present a measurement of the ttbar production cross section at a center of mass energy of 7 TeV performed by the ATLAS Collaboration. We select events with only one charged lepton (electron or muon), large transverse missing energy, and at least 3 jets. The data used for this analysis corresponds to integrated luminosity of 35 pb$^{-1}$. The likelihood method is used to distinguish the ttbar production from background. We also use information about the presence of b-quark jets to improve the separation between signal and background.   

Top pair production in the channel $t\bar{t}{\rightarrow}W(e/{\mu}+{\nu}_{e,{\mu}})W({\tau}_{\rm had}+{\nu}_{{\tau}_{\rm had}})bb$ at ATLAS

The measurement of the $t\overline{t}$ cross section in the $t\overline{t}\rightarrow l+\tau+X$ channel is an important test of the Standard Model. If the charged Higgs Boson exists as required by MSSM, and its mass is lower than that of top quark mass, then the top quark can have a significant branching ratio to $t\rightarrow H^{\pm}+b$. For large $\tan\beta$ the charged Higgs decays mainly to $\tau\nu$, making this channel sensitive to beyond the standard model physics. Also, the busy environment created by top quark decays will be an important test of ATLAS's $\tau$ particle identification. The status of this measurement using a boosted decision tree for $\tau$ identification with $7TeV$ ATLAS data will be presented.