The cusp effect in eta' --> eta pi pi decays

TL;DR

This paper investigates the cusp effect in eta' decays to eta pi pi, using an adapted effective field theory approach to predict a significant impact on the decay spectrum due to final-state interactions.

Contribution

It introduces a generalized non-relativistic effective field theory framework for eta' decays, extending methods used for pi pi scattering in kaon decays.

Findings

Cusp effect causes over 8% change in decay spectrum below pi+ pi- threshold.

Effective field theory adaptation allows precise modeling of eta' decay interactions.

Predicted observable impact facilitates future experimental verification.

Abstract

Strong final-state interactions create a pronounced cusp in eta' --> eta pi0 pi0 decays. We adapt and generalize the non-relativistic effective field theory framework developed for the extraction of pi pi scattering lengths from K --> 3 pi decays to this case. The cusp effect is predicted to have an effect of more than 8% on the decay spectrum below the pi+ pi- threshold.