A Study of the ttW Background Modelling for ttH Analyses

In this document we compare Monte Carlo generator distributions of the ttW processes at particle level, using simulations produced by ATLAS and CMS. The aim is to compare the modelling and associated theory uncertainties of this important background for ttH measurements targeting final states where the Higgs boson decays to electrons, muons or hadronically decaying tau leptons, in preparation for a full Run-2 ATLAS+CMS combination. As a first step, the pre-fit modelling and theory uncertainties as used in the experimental measurements are compared across a collection of characteristic variable distributions after applying the relevant analysis selections in CMS-PAS-HIG-17-004 and ATLAS-CONF-2019-045.