Abstract
We present a new Monte Carlo event generator for the production of a top-quark pair in association with a $W^\pm$ boson at hadron colliders in the POWHEG-BOX framework. We consider the next-to-leading-order QCD corrections to the $pp\to t\bar{t} W^\pm$ cross section, corresponding to the $\mathcal{O}(\alpha_s^3\alpha)$ and $\mathcal{O}(\alpha_s\alpha^3)$ terms in the perturbative expansion of the parton-level cross section, and model the decays of $W$ and top quarks at leading order retaining spin correlations. The fixed-order QCD calculation is further interfaced with the Pythia8 parton-shower event generator via the POWHEG method as implemented in the POWHEG-BOX. The corresponding code is now part of the public repository of the POWHEG-BOX. We perform a comparison of different event generators for both the case of inclusive production and the case of the two same-sign leptons signature at the Large Hadron Collider operating at a center-of-mass energy of $13$ TeV. We investigate theoretical uncertainties in the modelling of the fiducial volume stemming from missing higher-order corrections, the different parton shower matching schemes, and the modelling of decays. We find that the subleading contribution at $\mathcal{O}(\alpha_s\alpha^3)$ is particularly sensitive to differences in the matching scheme and higher-order parton shower effects. We observe that in particular jet observables can differ quite visibly although these differences play only a subordinate role in the description of physical observables once all contributions are combined.
Highlights
The production of top-quark pairs in association with electroweak gauge bosons (W, Z, γ) can be measured at the Large Hadron Collider (LHC) and future hadron colliders (HL-LHC, FCC-hh, and CppC) in a multitude of decay channels and provides new avenues to test the consistency of the Standard Model (SM) in processes that have been beyond the energy reach of existing colliders or statistically limited until recently
In this paper we have presented a new NLO partonshower Monte Carlo event generator for the hadronic production of a top-quark pair in association with a WÆ boson taking into account the dominant NLO corrections at Oðα3sαÞ and Oðαsα3Þ
Motivated by the current tension [6] between the stateof-the-art SM predictions for the ttWÆ cross section and the corresponding measurement derived when ttWÆ is extracted from a combined signal and background fit in ttH analyses, we performed a detailed generator comparison involving the POWHEG-BOX, MG5_aMC@NLO, and Sherpa
Summary
The production of top-quark pairs in association with electroweak gauge bosons (W, Z, γ) can be measured at the Large Hadron Collider (LHC) and future hadron colliders (HL-LHC, FCC-hh, and CppC) in a multitude of decay channels and provides new avenues to test the consistency of the Standard Model (SM) in processes that have been beyond the energy reach of existing colliders or statistically limited until recently. These processes represent some of the most important backgrounds for Higgs-boson precision measurements and searches of new physics beyond the Standard Model (BSM) In this context, the hadronic production of WÆ bosons in association with top-quark pairs is interesting both from a phenomenological and a theoretical point of view. In this paper we continue the investigation of modeling uncertainties of the ttWÆ process, by presenting a study based on a new implementation of the pp → ttWÆ production in the POWHEG-BOX framework [37]. As part of our study, we perform a detailed comparison between different NLO parton-shower Monte Carlo event generators at both the inclusive and the fiducial level in order to address modeling uncertainties.
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