On the simulated kinematic distributions of heavy meson decays

TL;DR

This paper examines the phase-space sampling algorithm of EvtGen in heavy meson decay simulations, revealing unphysical features and proposing a reweighting correction method.

Contribution

It identifies issues in EvtGen's sampling algorithm for semileptonic B decays and offers a practical reweighting solution to improve simulation accuracy.

Findings

Unphysical features in kinematic distributions due to neglected phase-space factors.

Reweighting method effectively corrects the invariant mass distribution.

Highlights importance of accurate phase-space sampling in flavour physics simulations.

Abstract

Modern measurements in flavour physics rely on accurate simulations of signal and background processes, provided by a wide range of general-purpose and specialised Monte-Carlo event generators. Due to the inclusion of a larger amount of specialised decays of heavy hadrons, EvtGen is often the tool of choice for many scenarios. We investigate the phase-space sampling algorithm of EvtGen and demonstrate that it generates unphysical features in kinematic distributions of semileptonic $B$ decays involving resonances, originating from neglected phase-space factors. We provide a short-term solution to correct the affected simulated samples through reweighting of the hadronic invariant mass distribution.