Problem Of Missing Resonances Research Articles

Excited state baryon spectroscopy from lattice QCD

We present a calculation of the Nucleon and Delta excited state spectra on dynamical anisotropic clover lattices. A method for operator construction is introduced that allows for the reliable identification of the continuum spins of baryon states, overcoming the reduced symmetry of the cubic lattice. Using this method, we are able to determine a spectrum of single-particle states for spins up to and including $J=\frac{7}{2}$, of both parities, the first time this has been achieved in a lattice calculation. We find a spectrum of states identifiable as admixtures of $SU(6)\ensuremath{\bigotimes}O(3)$ representations and a counting of levels that is consistent with the nonrelativistic $qqq$ constituent quark model. This dense spectrum is incompatible with quark-diquark model solutions to the ``missing resonance problem'' and shows no signs of parity doubling of states.

Screened potential and the baryon spectrum

We show that in a quark model scheme the use of a screened potential, suggested by lattice QCD, instead of an infinitely rising one with the interquark distance, provides a more adequate description of the high-energy baryon spectrum. In particular an almost perfect parallelism between the predicted and observed number of states comes out throwing new light about the so-called missing resonance problem.