Abstract:

There are hundreds elementary particles and the discovery of a new one is usually not an extraordinary event. However, as its name is meant to imply, the resonance that was recently reported by Belle and confirmned by CDF is peculiar in that it does not easily fit into any known scheme. This state is narrow and is seen in its decay to , which suggests that it is one of the "missing" charmonium states. However, its mass and decay properties do not match well potential model expectations for any of the usual charmonium suspects. The also has the intriguing feature that its mass is equal within rather small errors to the sum of the masses of the and mesons. This suggests that it may not be a meson, but is instead a molecular-like bound state. In this talk I will present the evidence for the , describe what we know about its properties in the context of expectations for various possible charmonium states, and discuss strategies for future investigations.