Low-lying 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(qq) 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 qqqqq 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 qqqqq admixtures.The lowest negative parity states in the baryon spectrum are the Λ(1405), 1 2 − and Λ(1520), 3 2 − resonances, which in the quark model with 3 valence quarks are described as a flavor singlet multiplet [9]. The qqq valence quark model with the pion exchange type hyperfine interaction correctly predicts the low energy of this multiplet, but cannot explain its spin-orbit splitting [4]. The bound state version of the Skyrme model predicts both the low energy and the spin-orbit splittings of this multiplet correctly, however [10,11]. This suggests that this multiplet should have a relatively large qqqqq component. The Λ(1405) may even have a dominantKN component [12], and a separate

Mixing of the low-lying three- and five-quarkΩstates with negative parity

“…This is different from the results of previous models [38,39] without considering the mixing between three-and five-quark configurations, which predicted the lowest Ω excitation state to be of spin 1/2. To summarize: In all interaction models the lowest states are found to be those with spin 3/2 and and lie at ∼ 1750 ± 50 MeV.…”

Prediction of NarrowN*andΛ*Resonances with Hidden Charm above 4 GeV

“…Gk, 13.30.Eg, 13.75.Jz Up to now, all established baryons can be ascribed into 3-quark (qqq) configurations [1], although some of them were suggested to be meson-baryon dynamically generated states [2][3][4][5][6][7][8] or states with large (qqqqq) components [9][10][11]. A difficulty to pin down the nature of these baryon resonances is that the predicted states from various models are around the same energy region and there are always some adjustable ingredients in each model to fit the experimental data.…”

Penta-Quark States with Strangeness, Hidden Charm and Beauty

“…However, the well established states (marked as four-star) only include six Σ states, two Ξ states and one Ω state. Especially, only ground state of Ω is confirmed as Ω(1670) 3 …”

“…Furthermore, these multiquark components can naturally explain the problem in the three-quark model. For instance, the mass order reverse problem is easily solved by including large penta-quark components in these baryon states [2][3][4][5].…”

“…On theoretical side, the unquenched quark model provides totally different predictions of 1/2 − strangeness baryons. For example, the classical quenched quark models [44] predict the 1/2 − Σ * and Ξ * to be around 1650 MeV and 1760 MeV, respectively, while the unquenched quark models expect them to be around 1400 MeV and 1550 MeV [3,4,13], or 1450 MeV and 1620 MeV [45][46][47], respectively. It is necessary to check the predictions of hyperon resonances in these unquenched quark models with new data.…”