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Register a new userObservation of Single Top Quark Production with the D0 Detector
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Reinhard Schwienhorst
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We report on the observation of single top quark production by the D0 collaboration using a dataset of 2.3 fb^-1 collected at the Fermilab Tevatron ppbar collider. Several multivariate techniques are combined to separate the single top signal from backgrounds. The measured single top cross section is 3.94+-0.88pb. The probability to measure a cross section at this value or higher in the absence of signal is 2.9*10^-7, corresponding to a 5.0 standard deviation significance for the presence of signal. The lower limit at the 95% C.L. on the CKM matrix element Vtb is |Vtb|>0.78. A separate measurement of the t-channel cross section gives 3.14 +0.94 -0.80 pb.
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Updates of electroweak single top quark production measurements by the D0 collaboration are presented using 5.4fb^-1 of proton-antiproton collision data from the Tevatron at Fermilab. Measurements of the t-channel, s-channel and combined single top quark production cross section are presented, including an updated lower limit on the CKM matrix element |V_tb|. Also reported are results from searches for gluon-quark flavor-changing neutral currents and W boson production.
Single-top production has been studied with the ATLAS detector using 0.7 fb-1 of 2011 data recorded at 7 TeV center-of-mass energy. The measurement of electroweak production of top-quarks allows probes of the Wtb vertex and a direct measurement of the CKM matrix element |V_tb|. It is also expected to be sensitive to new physics such as flavor changing neutral currents or heavy W production. The t-channel cross-section measurements are performed using both a cut-based and neural network approach, while a cut-based selection in the dilepton channel is used to derive a limit on the associated (Wt) production. An observed cross-section of 90 +32 -22 pb (65 +28 -19 pb expected) is obtained for the t-channel, which is consistent with the Standard Model expectation. For the Wt production, an observed limit of < 39.1 pb (40.6 pb expected) is derived, which corresponds to about 2.5 times the Standard Model expectation.
This paper reports on the first observation of electroweak production of single top quarks by the DZero and CDF collaborations. At Fermilabs 1.96 TeV proton-antiproton collider, a few thousand events are selected from several inverse femtobarns of data that contain an isolated electron or muon and/or missing transverse energy, together with jets that originate from the decays of b quarks. Using sophisticated multivariate analyses to separate signal from background, the DZero collaboration measures a cross section sigma(ppbar->tb+X,tqb+X) = 3.94 +- 0.88 pb (for a top quark mass of 170 GeV) and the CDF collaboration measures a value of 2.3_0.6 -0.5 pb (for a top quark mass of 175 GeV). These values are consistent with theoretical predictions at next-to-leading order precision. Both measurements have a significance of 5.0 standard deviations, meeting the benchmark to be considered unambiguous observation.
The ATLAS experiment at the LHC at CERN has analyzed 2010 and 2011 data looking for electroweak production of single top quarks in the lepton+jets and di-lepton final states. The production cross section for the t-channel process is measured to be 76 +41 -21 pb using 156 pb^-1 of 2011 data. A first limit is set on the Wt associated production process using lepton+jets and di-lepton events. The 95% CL upper limit on the Wt production cross section is 158 pb using 35 pb^-1 of 2010 data.
Single-top production processes have been studied using 0.7 fb-1 of data from 7 TeV center-of-mass energy proton-proton collisions collected with the ATLAS detector at the LHC. Single-top is electroweak top production and the standard model includes three production modes. Each contains a Wtb vertex, allowing the possibility of a direct measurement of the CKM matrix element |Vtb|. Single-top could also be sensitive to new physics, such as flavor changing neutral currents or heavy W bosons. Using cut-based selections, a limit of < 39.1 pb is set for dilepton Wt production and < 26.5 pb for s-channel production. For the t-channel measurement, both cut-based and neural network analyses are performed and the cross-section is measured to be 90 +32 -22 pb, where 65 +28 -19 pb is expected according to standard model.
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