EXOTIC HADRON STATES

Abstract

Many charmonium-like and bottomonium-like XY Z resonances have been observed by the Belle, Babar, CLEO and BESIII collaborations in the past decade. They are dicult to fit in the conventional quark model and thus are considered as candidates of exotic hadrons, such as multi-quark states, meson molecules, and hybrids. In this talk, we first briefly introduce the method of QCD sum rules and then provide a short review of the mass spectra of the quarkonium-like tetraquark states and the heavy quarkonium hybrids in the QCD sum rules approach. Possible interpretations of the XY Z resonances are briefly discussed.