Nucleon excitations in 2+1 flavor QCD

Abstract

A determination of the excited state spectrum of hadrons presents a significant challenge to the first-principles approach of Lattice QCD. Here a brief overview of the correlation-matrix methods developed recently by the CSSM Lattice Collaboration for the isolation of excited states of the nucleon is presented. The utility of the method is shown by exploring the first twelve states of the nucleon in the positive parity channel. Of particular interest is the Roper resonance, the first positive-parity excited-state of the nucleon. A low-lying Roper state is observed in full QCD calculations for the first time, showing significant curvature as the chiral regime is approached. The negative parity results are also explored, where the extracted first negative parity excited state approaches the physical value. © 2012 American Institute of Physics.