UC Berkeley

A determination of the top-quark mass is presented using 20.2 fb−1 of 8 TeV proton-proton collision data produced by the Large Hadron Collider and collected by the ATLAS experiment. The normalised differential cross section of top-quark pair production in association with an energetic jet is measured in the lepton+jets final state and unfolded to parton and particle levels. The unfolded distribution at parton level can be described using next-to-leading-order QCD predictions in terms of either the top-quark pole mass or the running mass as defined in the (modified) minimal subtraction scheme. A comparison between the experimental distribution and the theoretical prediction allows the top-quark mass to be extracted in the two schemes. The value obtained for the pole-mass scheme is:mtpole=171.1±0.4stat±0.9syst−0.3+0.7theoGeV$$ {m}_t^{\mathrm{pole}}=171.1\pm 0.4\left(\mathrm{stat}\right)\pm 0.9{\left(\mathrm{syst}\right)}_{-0.3}^{+0.7}\left(\mathrm{theo}\right)\;\mathrm{GeV} $$The extracted value in the running-mass scheme is:mtmt=162.9±0.5stat±1.0syst−1.2+2.1theoGeV.$$ {m}_t\left({m}_t\right)=162.9\pm 0.5\left(\mathrm{stat}\right)\pm 1.0{\left(\mathrm{syst}\right)}_{-1.2}^{+2.1}\left(\mathrm{theo}\right)\kern0.33em \mathrm{GeV}. $$The results for the top-quark mass using the two schemes are consistent, when translated from one scheme to the other.