Eur. Phys. J. C (2016) 76: 691
https://doi.org/10.1140/epjc/s10052-016-4538-2

Regular Article - Theoretical Physics

An NLO+PS generator for tt̅ and Wt production and decay including non-resonant and interference effects

¹ Università di Milano-Bicocca and INFN, Sezione di Milano-Bicocca, Piazza della Scienza 3, 20126, Milan, Italy
² INFN, Sezione di Milano-Bicocca, Piazza della Scienza 3, 20126, Milan, Italy
³ Physics Institute, Universität Zürich, Zurich, Switzerland

^* e-mail: lindert@physik.uzh.ch

Received: 9 August 2016
Accepted: 28 November 2016
Published online: 18 December 2016

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 pp → ℓ⁺ν_ℓl^-ν̅_lbb̅ at order α⁴α_s² plus full NLO QCD corrections, where the leptons ℓ and l belong to different families, and b quarks are massive. Thus, the contributions from tt̅ and Wt single-top production, plus contributions without top resonances and all relevant quantum interferences between different channels 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 tt̅ 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 POWHEG-BOX framework.