Quark models for mesons

Abstract

With the advance of experiment, many high excited states of meson are identified. It is found that many of them are difficult to fit into conventional q$ar{q}$q¯ meson spectra. Various explanations are proposed. One of them is the four-quark states or molecules of two mesons. In the framework of quark model, by taking into account of multi-body interaction, four-quark states are studied. The results show that the scalar mesons: f0(600), f0(980) and Y(2175) can be well described by four-quark states. Furthermore, unquenched quark model, which incorporates the four-quark components in the conventional q$ar{q}$ q¯ states, is constructed for mesons. By readjusting the model parameters, the model can give a good description of mesons. The model is also used to study the newly discovered XYZ particles.