Abstract
We present a Monte Carlo generator that implements significant theoretical improvements in the simulation of top-quark pair production and decay at the LHC. Spin correlations and off-shell effects in top-decay chains are described in terms of exact matrix elements for $p p \to \ell^+\nu_{\scriptscriptstyle\ell}\, l^-\bar{\nu}_{\scriptscriptstyle l} b \bar{b}$ at NLO QCD, where the leptons $\ell$ and $l$ belong to different families, and $b$ quarks are massive. Thus, the contributions from $t\bar{t}$ and $Wt$ single-top production as well as their quantum interference are fully included. Matrix elements are matched to the Pythia8 parton shower using a recently proposed method that allows for a consistent treatment of resonances in the POWHEG framework. These theoretical improvements are especially important for the interpretation of precision measurements of the top-quark mass, for single-top analyses in the $Wt$ channel, and for $t\bar{t}$ and $Wt$ backgrounds in the presence of jet vetoes or cuts that enhance off-shell effects. The new generator is based on a process-independent interface of the OpenLoops amplitude generator with the POWHEGBOX framework.
Highlights
Model (SM), and for measurements of fundamental parameters such as the top-quark mass
Spin correlations and off-shell effects in top-decay chains are described in terms of exact matrix elements for pp → +ν l−νl b bat order α4αS2 plus full next-to-leading order (NLO) QCD corrections, where the leptons and l belong to different families, and b quarks are massive
Matrix elements are matched to the Pythia8 parton shower using a recently proposed method that allows for a consistent treatment of resonances in the POWHEG framework
Summary
Model (SM), and for measurements of fundamental parameters such as the top-quark mass. A generator based on the POWHEG method and pp → +ν l−νl b bmatrix elements at NLO in the 5FNS has been presented in Ref. In this paper we present a NLO+PS generator, that we dub bb4l in the following, based on exact O(αs2α4) and O(αs3α4) matrix elements for pp → +ν l−νl b bin the 4FNS matched to Pythia8 [60,61] using the resonanceaware POWHEG method. This new generator combines, for the first time, the following physics features:. The POWHEG-BOX-RES framework together with the bb4l generator can be downloaded at http://powhegbox. mib.infn.it
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