Jet Mass Resolutions in ATLAS using Run 2 Monte Carlo Simulation

The jet mass resolution (JMR) and its uncertainty are amongst the limiting systematic effects for precision measurements and searches for physics beyond the Standard Model. This note presents the latest ATLAS Run 2 Monte Carlo-based determination of the JMR for anti-$k_\mathrm{t}$ jets of radius $R$ = 1.0 and $R$ = 0.4 used to reconstruct events with QCD, $H$ $\rightarrow$ $b\bar{b}$, top, and $W/Z$ jet topologies in $pp$ collisions at $\sqrt{s}$ = 13 TeV. Two different approaches for correcting the JMR in Monte Carlo simulation to match that of data and propagating the relevant uncertainties are compared. The first is based on Gaussian smearing of the jet mass and the second, forward-folding, is a transformation based on information derived in $in$ $situ$ measurements using Run 2 data and simulation.The propagation of uncertainties on the JMR is studied using these two approaches in order to demonstrate the impact of the assumption that the jet mass response has a Gaussian shape. The two methods are found to provide similar results for $W$ jets, but to differ when applied to top jets.