Exotic Hadron Spectroscopy at B-factories
The high luminosity B factories have brought discoveries of many new exotic hadronic states, especially, charmonium- or bottomonium-like states, collectively known as “XYZ” states. Many of them have mass, which cannot be explained by the conventional quark model, and moreover, have an electric charge, which require at least four quarks. These results have established existence of hadronic states beyond the quark model. In this talk, I will summarize the results obtained by the Belle experiment and future prospect.