The strangest non-strange meson is not so strange after all

TL;DR

This paper demonstrates that broad non-strange mesons like $f_0$(500) can be accurately described as resonances similar to narrower ones, challenging the assumption that broad resonances cannot fit Breit-Wigner models.

Contribution

It shows that broad resonances such as $f_0$(500) can be modeled with Breit-Wigner forms by considering the resonance pole angle, unifying their description with narrower resonances.

Findings

Broad $f_0$(500) fits Breit-Wigner resonance model.

Resonance pole angle explains background and phase differences.

Comparison with $Z$ boson and $ riangle(1232)$ supports the model.

Abstract

The broad non-strange meson $f_0$(500) is considered to be a non-Breit-Wigner resonance. It is generally assumed that if a resonance is broad it can hardly be described by a Breit-Wigner form. We show here that is not true neither for the broad Z boson, nor for the much narrower $\Delta(1232)$, and explain why the $f_0$(500) fits with them perfectly. Key differences between them boil down to a single parameter: the angle at which we see the resonance pole from the threshold, which explains the background, the residue phase, and the difference between the pole and Breit-Wigner parameters.