Abstract
We introduce an improvement to the FxFx matrix element merging procedure for pp → toverline{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 toverline{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 toverline{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 ∼30% increase over the NLO QCD prediction and large non-flat K-factors to differential distributions.
Highlights
The ttW process is studied theoretically in detail beyond NLO in QCD at the production level, which corresponds to the parton-unfolded level of the experimental analyses
The inclusion of the parton shower is crucial especially to describe the jet-related observables. This is done in two independent studies [10, 19], where the ttW production is evaluated at NLO including the O(αS3 α) and O(αSα3) corrections, followed by LO decays of the ttW resonances and matched to the parton shower
For this second part we focus on the cross section of the various multi-lepton signatures at the fiducial region and jet-related differential distributions in order to point out the effects of the FxFx merging
Summary
In the real emission diagrams entering the O(αS3 α) corrections, one can distinguish two types of contributions: the contributions where the extra emission is attached to a QCD vertex and the ones where it is attached to an EW vertex. The Sudakov factors include the real unresolved and soft virtual corrections resummed at LL and the parton shower will add emissions to the 0-jet sample below the merging scale The effects introduced this way mimic the higher order corrections for the ttW jQCD contributions but not for the ttW jWeak ones. For clustering with massive particles, the mass enters the lower bound on the respective clustering scale, which means that in phasespace configurations for which there are large QCD soft and/or collinear logarithms, the QCD partons are always clustered before the Weak bosons or top quarks This results in ttW jQCD contributions and not Weak jets. The effects of this implementation in the differential distributions, like the one in figure 2 will be shown and discussed in detail in section 4.1, after we introduce the input parameters and the calculation setup
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