Coupled-channel study of crypto-exotic baryons with charm

Identifying a zero-range exchange of vector mesons as the driving force for the s-wave scattering of pseudo-scalar mesons off the baryon ground states, a rich spectrum of molecules is formed. We argue that chiral symmetry and large-Nc considerations determine that part of the interaction which generates the spectrum. A bound state with exotic quantum numbers is predicted at mass 2.78 GeV. It couples strongly to the (D¯sN),(D¯Λ),(D¯Σ) channels. A further charm minus-one system is predicted at mass 2.84 GeV as a result of (D¯sΛ),(D¯Ξ) interactions. We suggest the existence of strongly bound crypto-exotic baryons, which contain a charm-anti-charm pair. Such states are narrow since they can decay only via OZI-violating processes. A narrow nucleon resonance is found at mass 3.52 GeV. It is a coupled-channel bound state of the (ηcN),(D¯Σc) system, which decays dominantly into the (η′N) channel. Furthermore two isospin singlet hyperon states at mass 3.23 and 3.58 GeV are observed as a consequence of coupled-channel interactions of the (D¯sΛc),(D¯Ξc) and (ηcΛ),(D¯Ξc′) states. Most striking is the small width of about 1 MeV of the lower state. The upper state may be significantly broader due to a strong coupling to the (η′Λ) state. The spectrum of crypto-exotic charm-zero states is completed with an isospin triplet state at 3.93 GeV and an isospin doublet state at 3.80 GeV. The dominant decay modes involve again the η′ meson. The two so far observed s-wave baryons with charm one are recovered. We argue that the Λc(2880) is not a s-wave state. In addition to those states we predict the existence of about ten narrow s-wave baryon states with masses below 3 GeV. A triplet of crypto-exotic states decaying dominantly into channels with an η′ is obtained with masses 4.24 and 4.44 GeV. In the charm-two sector we predict in addition to the chiral excitations of the ground states two triplets of bound states formed by channels involving open-charm mesons. The binding energy of the latter is larger than the one of the chiral excitations.