Abstract
Precise measurements of top quark couplings are presented. The measurements cover the single top tW cross section, the top-quark branching-fraction ratio R=B(t → Wb)/B(t → Wq) and the CKM matrix element Vtb from the single top cross sections. Top quark polarisation in the t-channel single-top quark production and dilepton tt, and W-helicity fraction measurements along with searches of top quark anomalous couplings in lepton plus jet channel are also presented. Finally measurements of top quark pair production in association with a W or Z boson or a photon are presented.
Highlights
The top quark is the heaviest known fundamental particle
The differential cross section connecting the three fractions can be written in terms of the cos(θ∗) variable, where θ∗ is the angle between the charged lepton in the W rest frame with respect to the direction of the W in the top quark rest frame
We report the exclution limits calculated for anomalous coupling with 7 TeV data [11], using both electron and muon channels in figure 2
Summary
The top quark is the heaviest known fundamental particle. Because of its high mass, the top quark decays before hadronization and it can be studied as a free particle. The selected events are used to measure the tt cross section through a likelihood fit on the jet multiplicity constraining the signal and background contributions. Same sign dilepton events are used for the measurement of the ttW process, where one lepton originates from the leptonic decay of one of the two top quarks and the other from the decay of the W. The polarization and spin correlation are studied at CMS in terms of angular asymmetries in the dilepton decay channel [9]. In the single top analysis the asymmetry is defined using the angle between the charged lepton and the recoiling jet in the t-channel [10], since the light quark recoiling against the top quark tend to have a direction parallel to the spin direction of the top.
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