Molecular and Exotic Dibaryons and Other Hadrons

Abstract

Experimental evidence has been growing for the existence of both molecular and exotic dibaryons. The former are dominated by hadron and the latter by quark-gluon degrees of freedom. Exotic dihadrons are of particular interest because their properties are closely related to the parameters and non-perturbative properties of QCD models. Molecular structures provide information about confinement. Purely exotic models, such as bag and valence quark models, ignore the multi-hadron phase of confinement. Multi-configuration quark models and R-matrix boundary condition models better represent the medium range repulsive effects leading to confinement, predicting higher excitation energies of the exotic resonances. The ^1S_0 exotic predicted at 2.70 GeV mass has been identified in pp spin observables, implying that there are several more even and odd parity exotics in the NN system between 2.6 and 3.0 GeV. The method also predicts exotic strange and doubly strange dibaryons (including a di-lambda unbound by about 0.13 GeV) and exotics in baryon and meson channels. The R-matrix formalism also describes the properties of molecular structures and enables a classification of these into several types. Observed and predicted examples of each type are discussed, including the recently observed d'.