A precise interpretation for the top quark mass parameter in ATLAS Monte Carlo simulation

This note relates the top quark mass parameter in simulated pp collisions with a 13 TeV centre-of-mass-energy produced by ATLAS to a well-defined field-theoretical mass scheme. A calibration for the top mass parameter in simulation is obtained by fitting the simulated jet mass distribution of large--radius jets containing hadronically-decaying top quark with large transverse momentum, with a particle-level calculation at next-to-leading-log precision. The relation between the top mass parameter in the nominal \POWHEG + \PYTHIA simulation and the MSR mass scheme is determined to be: \Delta^{MSR} = m_{t}^{\text{MC}} - m_{t}^{\text{MSR}} (1 \GeV) = 80^{+350}_{-400} \MeV, where the uncertainty is dominated by contributions from uncalculated higher orders in the NLL calculation, the fit methodology and underlying event modelling.