Nucleon resonance phenomenology from lattice QCD


The CLAS program at Jefferson Lab will focus on the low-lying odd-parity spin-1/2 and 3/2 baryon resonances of the nucleon. These baryons offer an interesting forum for investigating QCD and model predictions. Lattice QCD investigations of the electromagnetic properties of the low-lying odd-parity states of the nucleon and their transitions to the nucleon ground state will give us the first insights into the structure of orbitally excited baryons as predicted by QCD. The electromagnetic properties of these resonances may be very different from that predicted by model calculations where the angular momentum of the resonance is restricted to constituent quark degrees of freedom alone. Significant progress has been made on the exploration of these low-lying odd-parity baryons with improved lattice QCD actions. We have developed methods for removing even-parity ground-state contaminations from two-point correlation functions at both zero and finite momenta. We have investigated the properties of two odd-parity interpolating fields based on the established interpolating fields for the nucleon ground state. Isolation of the lowest-lying odd-parity state is very encouraging for future studies of odd-parity N → N* electromagnetic transition form factors. We are currently exploring new methods for investigating the properties of the odd-parity j = 3/2 nucleon resonance. Creating and isolating this resonance is computationally intensive, and we are evaluating new methods aimed at reducing the computational demands to a manageable level. Preliminary results display good splitting between the spin-3/2 nucleon resonance and the ground state and indicate future studies of the electromagnetic transition moments of these resonances are feasible

NUPP 2000