Excited baryons from Bayesian priors and overlap fermions

TL;DR

This study uses Bayesian methods and overlap fermions on lattice QCD to accurately determine excited baryon states, including the Roper resonance, showing results consistent with experimental observations.

Contribution

It introduces a Bayesian constrained-fitting approach with overlap fermions to extract excited baryon states on the lattice, achieving unprecedented clarity for the Roper resonance.

Findings

First clear observation of the Roper state as the first excited nucleon.

Level ordering of low-lying baryons matches experimental data.

Cross-overs between excited states occur in the pion mass range 300-400 MeV.

Abstract

Using the constrained-fitting method based on Bayesian priors, we extract the masses of the two lowest states of octet and decuplet baryons with both parities. The calculation is done on quenched 16^3x28 lattices of a=0.2 fm using an improved gauge action and overlap fermions, with the pion mass as low as 180 MeV. The Roper state N(1440)1/2+ is clearly observed for the first time as the 1st-excited state of the nucleon from the standard interpolating field. Together with other baryons, our preliminary results indicate that the level-ordering of the low-lying baryon states on the lattice is largely consistent with experiment. The realization is helped by cross-overs between the excited 1/2+ and 1/2- states in the region of pion mass from 300 to 400 MeV.