Radiative decays of the ϒ(2S) into the three χb states

Abstract The ARGUS detector at the e + e − storage ring DORIS II has been used as a pair spectrometer to study the photon transitions in the reaction ϒ (2S)→ γχ b (1 3 P 2,1,0 ). Three photon lines were observed with energies (110.6±0.3±0.9) MeV, (131.7±0.3±1.1) MeV and (162.1±0.5±1.4) MeV, respectively. The corresponding branching ratios were found to be (9.8±2.1±2.4)%, (9.1±1.8±2.2)% and (6.4±1.4±1.6)%. Upper limits for full widths at the 90% confidence limit are 1.0 MeV for the χb (1 3 P 2 ) and 2.6 MeV for the other two states.