Monte Carlo Simulation of Hard Radiation in Decays in Beyond the Standard Model Physics in Herwig++

TL;DR

This paper implements a POWHEG-based correction in Herwig++ to improve the simulation of hard radiation in decays relevant to Beyond the Standard Model physics, affecting observable distributions and event selection.

Contribution

It introduces a novel application of the POWHEG formalism to decay processes in Herwig++, enhancing the accuracy of radiation modeling in BSM scenarios.

Findings

The correction impacts the shapes of key experimental observables.

It modifies the number of events passing selection criteria.

Validation on Standard Model top decays confirms the approach's effectiveness.

Abstract

We use the POWHEG formalism in the Herwig++ event generator to match QCD real-emission matrix elements with the parton shower for a range of decays relevant to Beyond the Standard Model physics searches. Applying this correction affects the shapes of experimental observables and so changes the number of events passing selection criteria. To validate this approach, we study the impact of the correction on Standard Model top quark decays. We then illustrate the effect of the correction on Beyond the Standard Model scenarios by considering the invariant-mass distribution of dijets produced in the decay of the lightest Randall-Sundrum graviton and transverse momentum distributions for decays in Supersymmetry. We consider only the effect of the POWHEG correction on the simulation of the hardest emission in the shower and ignore the normalisation factor required to correct the total widths and branching ratios to next-to-leading order accuracy.