Automation of NLO processes and decays and POWHEG matching in WHIZARD

TL;DR

This paper reports on the automation of NLO calculations and their matching with parton showers in the WHIZARD event generator, enhancing precision for collider process simulations, especially for e+e- and lepton collider scenarios.

Contribution

It introduces automated NLO process implementation and POWHEG matching in WHIZARD, including divergence handling and phase space generation, with applications to lepton collider processes.

Findings

Successful automation of NLO calculations in WHIZARD.

First NLO studies for polarized lepton collisions at ILC.

Matching of NLO with parton shower improves differential observable predictions.

Abstract

We give a status report on the automation of next-to-leading order processes within the Monte Carlo event generator WHIZARD, using GoSam and OpenLoops as provider for one-loop matrix elements. To deal with divergences, WHIZARD uses automated FKS subtraction, and the phase space for singular regions is generated automatically. NLO examples for both scattering and decay processes with a focus on e+e- processes are shown. Also, first NLO-studies of observables for collisions of polarized leptons beams, e.g. at the ILC, will be presented. Furthermore, the automatic matching of the fixed-order NLO amplitudes with emissions from the parton shower within the POWHEG formalism inside WHIZARD will be discussed. We also present results for top pairs at threshold in lepton collisions, including matching between a resummed threshold calculation and fixed-order NLO. This allows the investigation of more exclusive differential observables.