Light hadron spectroscopy

Calculation of the hadron spectrum has been a central goal of Lattice QCD for 20 years. A precision calculation of the hadron spectrum would be a validation of QCD, and a validation of Lattice QCD as a calculational technique. It would give us con dence when we apply lattice QCD to calculating other quantities. In addition we would be able to clarify the nature of observed hadrons and predict where others might be found. True precision hadron mass calculations have been performed for heavy-quarkonium systems [1{3], and are beginning to appear for heavy-light systems [4]. Despite some monumental e orts such as that by the GF-11 group [5], the light hadron spectrum remains considerably less well determined than one might hope for. This is unfortunate, since this part of the hadron spectrum is the most complex and least well understood. The reasons for this situation are well known. The light hadrons (with possible exception of the glueballs) are large, their size being determined by the pion Compton wavelength, so that large lattices are needed. Small lattice spacings are needed to make contact with the continuum limit. The u and d quark masses are small, making the Dirac operator ill-conditioned and expensive to invert. There are a large number of excited states, which makes it di cult to isolate the ground state contribution to (almost) any hadron propagator. At small quark masses, hadron propagators be-