Scattering in the pion-nucleon negative parity channel in lattice QCD

TL;DR

This study uses lattice QCD to analyze the negative parity pion-nucleon system, revealing new energy levels and insights into the nucleon spectrum through combined baryon and meson-baryon operators.

Contribution

It introduces a combined operator approach and variational analysis to better understand the negative parity nucleon spectrum in lattice QCD.

Findings

Discovery of a new energy level in the negative parity channel

Significant differences from simple 3-quark correlation results

Estimation of phase shifts for elastic s-wave scattering

Abstract

We study the coupled pion-nucleon system (negative parity, isospin 1/2) based on a lattice QCD simulation for nf=2 mass degenerate light quarks. Both, standard 3-quarks baryon operators as well as meson-baryon (4+1)-quark operators are included. This is an exploratory study for just one lattice size and lattice spacing and at a pion mass of 266 MeV. Using the distillation method and variational analysis we determine energy levels of the lowest eigenstates. Comparison with the results of simple 3-quark correlation studies exhibits drastic differences and a new level appears. A clearer picture of the negative parity nucleon spectrum emerges. For the parameters of the simulation we may assume elastic s-wave scattering and can derive values of the phase shift.