P. Katrenko et al. (Belle Collaboration)WEI-SHU HOU2021-07-282021-07-282020319007https://www.scopus.com/inward/record.uri?eid=2-s2.0-85083545972&doi=10.1103%2fPhysRevLett.124.122001&partnerID=40&md5=18d174b67cea62ce4c02dd93602e00d0https://scholars.lib.ntu.edu.tw/handle/123456789/574661We report the first observation of the radiative decay of the ψ(1S) into a charmonium state. The significance of the observed signal of ψ(1S)→γχc1 is 6.3 standard deviations including systematics. The branching fraction is calculated to be B[ψ(1S)→γχc1]=[4.7-1.8+2.4(stat)-0.5+0.4(sys)×10-5]. We also searched for ψ(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 ψ(2S) mass using ψ(1S) tagging by the ψ(2S)→ψ(1S)π+π- transitions. ? 2020 authors. Published by the American Physical Society.Atomic physics; Asymmetric energy; Belle detectors; Branching fractions; Data sample; E+e- collider; Radiative decay; Standard deviation; Upper limits; Physics; article; taxonomy[SDGs]SDG7journal article10.1103/PhysRevLett.124.122001322818352-s2.0-85083545972