Robert Edwards

Results and Frontiers in Lattice Baryon Spectroscopy

The Lattice Hadron Physics Collaboration (LHPC) baryon spectroscopy effort is reviewed. To date the LHPC has performed exploratory Lattice QCD calculations of the low‐lying spectrum of Nucleon and Delta baryons. These calculations demonstrate the effectiveness of our method by obtaining the masses of an unprecedented number of excited states with definite quantum numbers. Future work of the project is outlined.

Hadronic Resonances from Lattice QCD

The determination of the pattern of hadronic resonances as predicted by Quantum Chromodynamics requires the use of non‐perturbative techniques. Lattice QCD has emerged as the dominant tool for such calculations, and has produced many QCD predictions which can be directly compared to experiment. The concepts underlying lattice QCD are outlined, methods for calculating excited states are discussed, and results from an exploratory Nucleon and Delta baryon spectrum study are presented.

First-principles calculation of excited state spectra in QCD

Recent progress at understanding the excited state spectra of mesons and baryons is described. I begin by outlining the application of the variational method to compute the spectrum of QCD, and then present results for the excited meson spectrum, with continuum quantum numbers of the states clearly delineated. I emphasise the need to extend the calculation to encompass multi‐hadron contributions, and describe a recent calculation of the I = 2ππ energy‐dependent phase shifts as a precursor to the study of channels with resonant behavior. I conclude with recent results for the low lying baryon spectrum, and the prospects for future calculations.

Group Theoretical Construction of Baryon Operators using All-to-All Quark Propagators

We describe a method to construct irreducible baryon operators using all-to-all quark propagators. It was demonstrated earlier that a large basis of exten ded baryon operators on anisotropic, quenched lattices can be used to reliably extract the masses of 5 or more excited states in the nucleon channel. All-to-all quark propagators are expected to be needed when studying these excited states on light, dynamical configurations because c ontributions from multi-particle states are expected to be significant. The dilution method is used to approximate the all-to-all quark propagators. Low-lying eigenmodes can also be used if necessary. For efficient computation of matrix elements of the interpolating operators, the algori thms should exploit the fact that many extended baryon operators can be obtained from the different linear combinations of three-quark colour-singlet operators. The sparseness of the diluted no ise vectors also afford several computation simplifications. Some preliminary results are present ed for nucleon effective masses.

Hadron spectrum with domain-wall valence quarks on an improved staggered sea

The hadron spectrum is computed in full QCD using domain-wall valence fermions on an improved staggered sea, for pion masses down to around

Pion form factor in Lattice QCD with light pions

350{approx}(/rm MeV)

An a

. Emphasis is laid on the low-lying baryon spectrum. All possible baryon correlators obtainable from local and quasi-local quark sources are computed, using lattice group-theory methods Results are presented for the lowest-lying states in each isospin channel.

_{0}

Exotic and higher spin (> 1) mesons are still not throughly investigated in lattice QCD. Using a set of derivative based operators we report our exploratory study of these mesons in charmonium region. We use a 12^3 x 48 anisotropic (xi = 3) clover lattice with temporal lattice spacing a^-1 = 6.05 GeV. Techniques developed in this exploratory study will be utilized in our future comprehensive study of light hybrid mesons that are to be explored in the 12 GeV GlueX experiment at Jefferson Laboratory.