With the 13 TeV LHC run, both ATLAS and CMS collaborations have measured the p p > t t V (V=Z,W) cross sections and these processes are studied either independently or as irreducible backgrounds to ttH searches. In both these studies a tension between theoretical predictions and data is observed for ttW. With the increasing luminosity the latest results allow us to distinguish between the different signatures (same sign dilepton, trilepton, etc.) and therefore compare the results with the theoretical predictions at different jet multiplicities. This increases the challenge to the experimental as well as the theoretical side for a better understanding of this process.
From the theoretical point of view, ttW production is recently calculated at NLO+NNLL accuracy at the cross section and differential level, with the NLO standing for both QCD and EW corrections. The role of including the resummation as well as the subleading EW corrections will be discussed. Furthermore once moving to the decay level, which is necessary for more realistic comparisons, this accuracy cannot be maintained. For this reason the discussion will include ideas on the best way to simulate the process up to the final signatures.
From the experimental point of view, recent ttH multileptons preliminary analyses from both ATLAS and CMS have studied ttW process as an unconstrained background. CMS measured ttW signal strength, while ATLAS extracted ttW normalization factors simultaneously with ttH signal extraction. ATLAS observed a mismodeling in charge asymmetry as well as in high b-jet multiplicities in regions where ttW process is enriched. ttH signal strength extraction is performed by ascribing systematic uncertainties to these observed mismodelings. The latest ATLAS ttH multileptons measurement will be discussed with a detailed focus on ttW background modeling and associated systematics used.