Observation of the Radiative Decays of <math><mi>ϒ</mi><mo>(</mo><mn>1</mn><mi>S</mi><mo>)</mo></math> to <math><msub><mi>χ</mi><mrow><mi>c</mi><mn>1</mn></mrow></msub></math>

We report the first observation of the radiative decay of the ϒ(1S) into a charmonium state. The significance of the observed signal of ϒ(1S)→γχc1 is 6.3 standard deviations including systematics. The branching fraction is calculated to be B[ϒ(1S)→γχc1]=[4.7−1.8+2.4(stat)−0.5+0.4(sys)&#215;10−5]. We also searched for ϒ(1S) radiative decays into χc0,2 and ηc(1S,2S), and set upper limits on their branching fractions. These results are obtained from a 24.9 fb−1 data sample collected with the Belle detector at the KEKB asymmetric-energy e+e− collider at a center-of-mass energy equal to the ϒ(2S) mass using ϒ(1S) tagging by the ϒ(2S)→ϒ(1S)π+π− transitions.