On improving NLO merging for $t\bar{t}W$ production

Abstract

We introduce an improvement to the FxFx matrix element merging procedure for $pp\to t\bar{t}W$ production at NLO in QCD with one and/or two additional jets. The main modification is an improved treatment of jets that are not logarithmically enhanced in the low transverse-momentum regime. We provide predictions for the inclusive cross section and the $t\bar{t}W$ differential distributions including parton-shower effects. Taking also the NLO EW corrections into account, this results in the most-accurate predictions for this process to date. We further proceed to include the on-shell LO decays of the $t\bar{t}W$ including the tree-level spin correlations within the narrow-width approximation, focusing on the multi-lepton signatures studied at the LHC. We find a $\sim 30\%$ increase over the NLO QCD prediction and large non-flat $K$-factors to differential distributions.

Comments: 21 pages, 8 figures, 4 tables