Determination of the top-quark mass from top-quark pair events with the matrix element method at next-to-leading order

In 2004 the matrix element method was used in a pioneering work by the Tevatron experiment 𝐷⁢0 to determine the top-quark mass from a handful of events. Since then the method has matured into a powerful analysis tool. While the first applications were restricted to leading-order accuracy, the extension to next-to-leading order (NLO) accuracy has also been studied. In this article we explore the potential of the matrix element method at NLO to determine the top-quark mass using events with pair-produced top quarks. We simulate a toy experiment by generating unweighted events with a fixed input mass and apply the matrix element method to construct an estimator for the top-quark mass. Two different setups are investigated; unweighted events obtained from the fixed-order cross section at NLO accuracy as well as events obtained using POWHEG matched to a parton shower. The latter lead to a more realistic simulation and allow to study the impact of higher-order corrections as well as the robustness of the approach. We find that the matrix element method in NLO accuracy leads to a significant reduction of the theoretical uncertainties compared to leading order. In view of the high-luminosity phase of the LHC, this observation is especially relevant in analyses which are no longer dominated by statistical uncertainties.