# Physical properties of resonances as the building blocks of multichannel scattering amplitudes

## TL;DR

This paper introduces a simple, physically motivated formula for multichannel resonant scattering that accurately predicts scattering amplitude features near resonances, including overlapping ones, without background fitting.

## Contribution

It presents a novel, straightforward formula linking resonant properties to scattering amplitudes, enhancing understanding of resonance behavior without complex background modeling.

## Key findings

- Accurately predicts residue phase from other resonant parameters.
- Describes scattering amplitude shapes near resonances effectively.
- Explains features of complex models by enforcing unitarity.

## Abstract

We propose a simple formula for multichannel resonant scattering with parameters related to physical resonant properties. It can be used to predict residue phase from other resonant parameters and describe the shape of scattering amplitudes close to the resonance without any background contributions or fitting. It works well even for overlapping resonances. Imposing unitarity to the proposed formula enabled us to explain some puzzling features of much more advanced models.