J. Hofmann, M. F. M. Lutz
Abstract
Identifying the t-channel exchange of vector mesons as the driving force for the s-wave scattering of pseudo-scalar mesons off the baryon ground states, a surprisingly rich spectrum of molecules is formed. We argue that chiral symmetry and large- N_c considerations determine that part of the interaction which generates the spectrum. All channels that are required by the existence of (u,d,s,c) quarks are considered. A bound state with exotic quantum numbers is predicted at mass 2.78 GeV. It couples strongly to the (bar D_s N),(bar D Lambda),(bar D Sigma) channels. A further charm minus-one system is predicted at mass 2.84 GeV as a result of (bar D_s Lambda), (bar D Xi) 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 (eta_c N), (bar D Sigma_c) system, which decays dominantly into the (eta' N) channel. Furthermore two isospin singlet hyperon states at mass 3.23 GeV and 3.58 GeV are observed as a consequence of coupled-channel interactions of the (bar D_s Lambda_c), (bar D Xi_c) and (eta_c Lambda),(bar D Xi_c') 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 (eta' Lambda) state. The two so far observed s-wave baryons with charm one are recovered. We argue that the Lambda_c(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.