Measurement of the top quark decay branching fraction ratio R_b = B(t → Wb)/B(t → Wq) and of the inclusive production cross section pp → tt in the dilepton channel at ATLAS

Abstract

The top quark branching fraction ratio Rb and the inclusive production cross section σ tt̄ are measured in the dilepton channel using 4.6 fb-1 of proton-proton collisions at the centre-of-mass energy √ s = 7 TeV collected with the ATLAS detector at the Large Hadron Collider at CERN. Template fits to the distribution of the number of b-tagged jets find Rb = 1.02 ± 0.01 (stat.) ± 0.07 (syst.) and σtt̄= 178 ± 3 (stat.) ± 19 (syst.) pb. Lower limits on Rb and on the CKM matrix element |Vtb| are set with the measured value of Rb to Rb > 0.88 and |Vtb| > 0.94 at 95% confidence level