Low lying $qqqq\bar{q}$ states in the baryon spectrum

Abstract

The coupling to light mesons leads to large widths and shifts of the energy of the excited states in the baryon spectrum from the predictions of the constituent quark model with three valence quarks. This coupling may be modelled by admixtures of sea-quark $qqq(q\bar{q}{)}^n$ configurations in the resonances. A schematic flavor and spin dependent interaction model, similar to the one which reproduces the low lying part of the experimental baryon spectrum in the valence quark model, is shown to bring the lowest $qqqq\bar{q}$ states with L=1 and positive parity below the states with L=0. Because of the partial overlap with the corresponding $qqq$ states this suggests that most of the low lying states in the baryon resonance spectrum have substantial $qqqq\bar{q}$ admixtures.

Comments: Substantially revised version, with confining interaction modified and flavor SU(3) breaking effects partly taken into account. 46 pages, LaTeX, 10 Postscript figures, to be published in Nucl. Phys. A