Understanding the nature of baryon resonances

TL;DR

This paper reviews lattice QCD findings on baryon excitations, compares them with experimental data, and discusses how combining these approaches can resolve longstanding issues in understanding baryon resonances.

Contribution

It introduces a novel approach of integrating lattice QCD calculations with experimental scattering data to better understand baryon resonance structures.

Findings

Lattice QCD shows the 2s nucleon excitation at ~2 GeV, above the Roper resonance.

Coupled-channel analysis can be adapted to finite-volume lattice QCD.

This approach offers a new perspective on the missing baryon resonances problem.

Abstract

This presentation opens with a brief review of lattice QCD calculations showing the $2s$ radial excitation of the nucleon sits at approximately 2 GeV, well above the Roper resonance position. We then proceed to reconcile this observation with experimental scattering data. While the idea of dressing quark-model states in a coupled-channel analysis to describe scattering data has been around for decades, it's now possible to bring these descriptions to the finite-volume of lattice QCD for confrontation with lattice-QCD calculations. This combination of lattice QCD and experiment demands that we reconsider our preconceived notions about the quark-model and its excitation spectrum. We close with a discussion of an unanticipated resolution to the missing baryon resonances problem.