Baryon spectroscopy

Understand

About 120 baryons and baryon resonances are known, from the abundant nucleon with $u$ and $d$ light-quark constituents up to the recently discovered $\Omega_b^-=bss$, and the $\Xi_b^-=bsd$ which contains one quark of each generation.

• In spite of this impressively large number of states, the underlying mechanisms leading to the excitation spectrum are not yet understood.
• Heavy-quark baryons suffer from a lack of known spin-parities.
• In the light-quark sector, quark-model calculations have met with considerable success in explaining the low-mass excitations spectrum but some important aspects like the mass degeneracy of positive-parity and negative-parity baryon excitations are not yet satisfactorily understood.