Illustration: Alan Stonebraker; bottom panel courtesy of P. Grenier and the BaBar collabora

Figure 1: (Top) The $bb¯$ spectrum showing electromagnetic transitions between levels. The states that have been observed are labeled with masses taken from the Particle Data Book [16] and unobserved states are shown unlabelled with masses given by Godfrey and Isgur [9]. The unlabeled arrows show electric dipole transitions and the labeled transition (green arrow) is the $M1$ transition observed by the BABAR collaboration in their discovery of the $ηb$. The dashed line indicates the threshold above which $bb¯$ will have large decay rate to $B-B¯$ 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 $ηb$ signal (red) [3].