QCD multijet events, where DY corresponds to processes such as $\qqbar\to\ell^{+}\ell^{-}$. Smaller contributions arise from single top quark production and rare SM processes, such as triboson and Higgs boson production, and top quark pair production in association with vector bosons. We rely on a combination of measurements in data CRs and Monte Carlo (MC) simulation to estimate contributions of each source of background. The MC simulation is also used to model the signal.

=800 The version 2.3.3 and 2.4.2 event generators [@Alwall:2014hca] are used at leading order (LO) precision to generate simulated [$\PW$+jets]{}and DY+jets events with up to 4 additional partons for the analysis of 2016 and 2017 data, respectively. Exclusive event samples binned in jet multiplicity are used to enhance the statistical power of the simulation at higher values of jet multiplicity that are relevant to the phase space probed by this search. Production of top quark pairs, diboson and triboson events, and rare SM processes, such as single top quarks or top quark pairs associated with bosons, are generated at next-to-leading order (NLO) precision with and v2 [@Nason:2004rx; @Frixione:2007vw; @Alioli:2010xd; @Re:2010bp]. Showering and hadronization of partons are carried out using the  8.205 and 8.230 packages [@Sjostrand:2014zea] for the 