Off-shell single-top production at NLO matched to parton showers
Rikkert Frederix, Stefano Frixione, Andrew S. Papanastasiou, Stefan Prestel, Paolo Torrielli
TL;DR
This work provides a first resonance-aware MC@NLO treatment of t-channel single-top hadroproduction with full off-shell and non-resonant top-width effects, matched to two major parton showers. It demonstrates how phase-space remapping and FKS subtraction can be adapted to handle colored intermediate resonances and quantifies the impact of off-shellness and shower modelling on a broad set of observables. By systematically comparing full off-shell W^+ b j predictions to on-shell tj and MadSpin approaches, the paper reveals substantial shower- and decay-related effects, and highlights the limitations of approximations in precision top-quark studies. The study offers a general framework applicable to other matrix elements with colored resonances and underscores the importance of shower choice and resonance handling for accurate phenomenology at the LHC.
Abstract
We study the hadroproduction of a $Wb$ pair in association with a light jet, focusing on the dominant $t$-channel contribution and including exactly at the matrix-element level all non-resonant and off-shell effects induced by the finite top-quark width. Our simulations are accurate to the next-to-leading order in QCD, and are matched to the HERWIG6 and PYTHIA8 parton showers through the MC@NLO method. We present phenomenological results relevant to the 8 TeV LHC, and carry out a thorough comparison to the case of on-shell $t$-channel single-top production. We formulate our approach so that it can be applied to the general case of matrix elements that feature coloured intermediate resonances and are matched to parton showers.