Using 106 ×106 ψ(3686) events collected with the BESIII detector, we measure multipole amplitudes for the decay ψ(3686)→γχc1,2→γγJ/ψ beyond the dominant electric-dipole amplitudes. The normalized magnetic-quadrupole (M2) amplitude for ψ(3686)→γχc1,2→γγJ/ψ and the normalized electric-octupole amplitudes for ψ(3686)→γχc2, χc2→γJ/ψ are determined. The M2 amplitudes for ψ(3686)→γχc1 and χc1,2→γJ/ψ are found to differ significantly from zero and are consistent with theoretical predictions. We also obtain the ratios of M2 contributions of ψ(3686) and J/ψ decays to χc1,2, b21/b22=1.35±0.72 and a21/a22=0.617±0.083, which agree well with theoretical expectations. By considering the multipole contributions of χc1,2, we measure the product branching fractions for the cascade decays ψ(3686)→γχc0,1,2→γγJ/ψ and search for the process ηc(2S)→γJ/ψ through ψ(3686)→γηc(2S). The product branching fraction for ψ(3686)→γχc0→γγJ/ψ is 3σ larger than published measurements, while those of ψ(3686)→γχc1,2→γγJ/ψ are consistent. No significant signal for the decay ψ(3686)→γηc(2S)→γγJ/ψ is observed, and the upper limit of the product branching fraction at the 90% confidence level is determined.
Bibliographical noteFunding Information:
This work is supported in part by National Key Basic Research Program of China under Contract No. 2015CB856700; National Natural Science Foundation of China (NSFC) under Contracts No. 11125525, No. 11235011, No. 11322544, No. 11335008, No. 11425524, No. 11475187, No. 11521505, and No. 11575198; the Chinese Academy of Sciences (CAS) Large-Scale Scientific Facility Program; the CAS Center for Excellence in Particle Physics; the Collaborative Innovation Center for Particles and Interactions; Joint Large-Scale Scientific Facility Funds of the NSFC and CAS under Contracts No. 11179007, No. U1232201, and No. U1332201; CAS under Contracts No. KJCX2-YW-N29 and No. KJCX2-YW-N45; 100 Talents Program of CAS; National 1000 Talents Program of China; Institute of Nuclear and Particle Physics (INPAC) and Shanghai Key Laboratory for Particle Physics and Cosmology; German Research Foundation under Collaborative Research Center Contract No. CRC-1044; Istituto Nazionale di Fisica Nucleare, Italy; Koninklijke Nederlandse Akademie van Wetenschappen under Contract No. 530-4CDP03; Ministry of Development of Turkey under Contract No. DPT2006K-120470; NSFC under Contracts No. 11405046 and No. U1332103; Russian Foundation for Basic Research under Contract No. 14-07-91152; The Swedish Research Council; U.S. Department of Energy under Contracts No. DE-FG02-04ER41291, No. DE-FG02-05ER41374, No. DE-SC0012069, No. DESC0010118; U.S. National Science Foundation; University of Groningen and the Helmholtzzentrum fuer Schwerionenforschung GmbH, Darmstadt; and World-Class University (WCU) Program of National Research Foundation of Korea under Contract No. R32-2008-000-10155-0.
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