(Top) The spectrum showing electromagnetic transitions between levels. The states that have been observed are labeled with masses taken from the Particle Data Book  and unobserved states are shown unlabelled with masses given by Godfrey and Isgur . The unlabeled arrows show electric dipole transitions and the labeled transition (green arrow) is the transition observed by the BABAR collaboration in their discovery of the . The dashed line indicates the threshold above which will have large decay rate to final states. (Bottom) The inclusive photon spectrum observed by BABAR is shown, including the background components (green, blue) that must be subtracted to obtain the signal (red) .