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 R_b 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 R_b = 1.02 ± 0.01 (stat.) ± 0.07 (syst.) and σ_tt̄= 178 ± 3 (stat.) ± 19 (syst.) pb. Lower limits on R_b and on the CKM matrix element |V_tb| are set with the measured value of R_b to R_b > 0.88 and |V_tb| > 0.94 at 95% confidence level.