Abstract
Measurements of the branching ratios of top quark decays into leptons and jets using events with $t \overline{t}$ (top antitop) pairs are reported. Events were recorded with the ATLAS detector at the LHC in pp collisions at a center-of-mass energy of 7 TeV. The collected data sample corresponds to an integrated luminosity of 4.6 ${\mathrm{fb}}^{-1}$. The measured top quark branching ratios agree with the Standard Model predictions within the measurement uncertainties of a few percent.
Highlights
In the Standard Model (SM), 100% of the top quark decays contain a W boson and a down-type quark
In the SM the branching ratio to the different leptons is the same since the decay proceeds via a W boson, but in models of new physics, e.g. supersymmetry (SUSY), final states with τ leptons can be enhanced or suppressed [5]; measuring the inclusive cross section using final states with τ leptons can be a good probe for new physics
The measured values of the top quark branching ratios will deviate with respect to the SM predictions if the data sample selected to extract tt events contains final states without two W bosons
Summary
In the Standard Model (SM), 100% of the top quark decays contain a W boson and a down-type quark. Limits on the top quark branching ratio to a charged Higgs boson and a b-quark have been published by the CDF [6], D0 [7,8], ATLAS [9,10] and CMS [11] collaborations Another example of a final state that can change the observed branching ratios is the pair production of supersymmetric partners of the top quark (~t) decaying into bνττ~ followed by the τ~ decay into a τ lepton and the gravitino, predicted by gauge-mediated SUSY breaking models [12]. Branching ratios for semileptonic and purely hadronic top quark decays are obtained by combining these seven final states assuming that only SM processes contribute to the background and the top branching ratios to leptons and jets add up to one
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