Monte Carlo Top Quark Mass Calibration

The most precise top quark mass measurements use kinematic reconstruction methods, determining the top mass parameter of a Monte Carlo event generator, m^MCt. Due to the complicated interplay of hadronization and parton shower dynamics in Monte Carlo event generators relevant for kinematic reconstruction, relating m^MCt to field theory masses is a non-trivial task. In this talk we report on a calibration procedure to determine this relation using hadron level QCD predictions for 2-Jettiness in e+e− annihilation, an observable which has kinematic top mass sensitivity and a close relation to the invariant mass of the particles coming from the top decay. The theoretical ingredients of the QCD prediction are reviewed. Fitting e+e− 2-Jettiness calculations at NLL/NNLL order to \Pythia~8.205, we find that m^MCt agrees with the MSR mass m^MSRt,1GeV within uncertainties. At NNLL we find m^MCt=m^MSRt,1GeV+(0.18±0.22)GeV. m^MCt can differ from the pole mass mpolet by up to 600MeV, and using the pole mass generally leads to larger uncertainties. At NNLL we find m^MCt=m^polet+(0.57±0.28)GeV as the fit result. In contrast, converting mMSRt,1GeV obtained at NNLL to the pole mass gives a result for m^polet that is substantially larger and incompatible with the fit result. We also explain some theoretical aspects relevant for employing the C-parameter as an alternative calibration observable.