Anatomy of Roper Resonance

TL;DR

This paper reviews the historical development and complex pole structure of the Roper resonance, highlighting its unique nature as a single resonance with multiple pole positions across different Riemann sheets.

Contribution

It provides a comprehensive historical overview and analysis of the Roper resonance's pole structure, emphasizing its distinctive features in hadron physics.

Findings

The Roper resonance has two pole positions on different Riemann sheets.

Historical development of understanding the Roper resonance is summarized.

The resonance's unique properties are highlighted in the context of hadron physics.

Abstract

Sixty years ago, the first excited state of a proton/neutron was ``born.'' During this time, we learned a lot about it, specifically - how unique this case is: a single resonance with two pole positions on different Riemann sheets. Let me present a brief history to remind readers how development progressed. Sure, history is sometimes something that never happened, described by those who were never there...