Top quark mass calibration for Monte-Carlo event generators

The most precise top quark mass measurements use kinematic reconstruction methods, determining the top mass parameter of a Monte Carlo event generator, mMCt. Due to the complicated interplay of hadronization and parton shower dynamics in Monte Carlo event generators, relating mMCt to field theory masses is a non-trivial task. In this talk we present 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 has a close relation to the invariant mass of the particles coming from the top decay. The theoretical ingredients of the QCD prediction are explained. Fitting e+e- 2-Jettiness calculations at NLL/NNLL order to PYTHIA 8.205, we find that mMCt agrees with the MSR mass at the scale 1 GeV within uncertainties, mMCt ≃ mMSRt;1GeV, but differs from the pole mass by 900/600MeV.