Observation of Radiative Decays of theϒ(2S)

Abstract

Evidence is reported from the CLEO detector for the ${\chi }_b\mathrm{}\left(1P\right)\mathrm{}$ states from radiative decays of the $\Upsilon \mathrm{}\left(2S\right)\mathrm{}$. Photons are detected by pair conversion in the beam pipe or a lead radiator, and the pair momenta are measured in the drift chamber. Two photon lines are well resolved, with energies 109.5±0.7±1 and 129.0±0.8±1 MeV.