Determination of the top-quark mass from the m(lb) distribution in dileptonic ttbar events at sqrt(s) = 8 TeV

A measurement of the top-quark mass is presented using the distribution of the invariant mass $m_{lb}$ of the lepton and the b-quark originating from top-quark decays. The analysed dataset of pp-collisions at a centre-of-mass energy $\sqrt{s}=8$ TeV was recorded by the CMS experiment at the LHC, and corresponds to an integrated luminosity of 19.7 fb$^{-1}$. Top-quark pair candidate events are selected with two opposite-charge isolated leptons, one electron and one muon, and at least two jets in the final state. Using the $m_{lb}$ shape prediction from MadGraph a top-quark mass of $172.3\pm1.3$ GeV is obtained, consistent with previous measurements and with the world average. In addition, a study is presented in which the shape and/or normalisation of the measured $m_{lb}$ distribution are used to extract the top-quark mass using different theory predictions, the MadGraph simulation as well as a fixed-order QCD calculation.