Hadronic Spectrum - Multiquark States

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Many newly discovered mesons behave like charmonium states in that they preferentially decay into final states that contain a c- and a c-quark, but do not fit expectations for any of the unfilled levels of the conventional spectrum. There is a growing suspicion that at least some of these states are exotic, i.e. have a substructure that is more complex than the quark-antiquark mesons of the classical constituent quark model. Some of these candidate states have a non-zero electric charge and, thus, a minimal quark content of ud or du. In addition, states with similar properties have been observed in the b- and s-quark sectors. In this report, the experimental situation is briefly reviewed.