Based on 448.1×106 ψ(3686) events collected with the BESIII detector, the decays ψ(3686)→γχcJ,χcJ→γγ(J=0,1,2) are studied. The decay branching fractions of χc0,2→γγ are measured to be B(χc0→γγ)=(1.93±0.08±0.05±0.05)×10-4 and B(χc2→γγ)=(3.10±0.09±0.07±0.11)×10-4, which correspond to two-photon decay widths of Γγγ(χc0)=2.03±0.08±0.06±0.13 keV and Γγγ(χc2)=0.60±0.02±0.01±0.04 keV with a ratio of R=Γγγ(χc2)/Γγγ(χc0)=0.295±0.014±0.007±0.027, where the uncertainties are statistical, systematic and associated with the uncertainties of B(ψ(3686)→γχc0,2) and the total widths Γ(χc0,2), respectively. For the forbidden decay of χc1→γγ, no signal is observed, and an upper limit on the two-photon width is obtained to be Γγγ(χc1)<5.3 eV at the 90% confidence level. The ratio of the two-photon widths between helicity-zero and helicity-Two components in the decay χc2→γγ is also measured to be f0/2=Γγγλ=0(χc2)/Γγγλ=2(χc2)=(0.0±0.6±1.2)×10-2, where the uncertainties are statistical and systematic, respectively.
Bibliographical noteFunding Information:
The BESIII collaboration thanks the staff of BEPCII and the IHEP computing center for their strong support. 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 Nos. 11235011, 11322544, 11335008, 11425524, 11635010; the Chinese Academy of Sciences (CAS) Large-Scale Scientific Facility Program; the CAS Center for Excellence in Particle Physics (CCEPP); the Collaborative Innovation Center for Particles and Interactions (CICPI); Joint Large-Scale Scientific Facility Funds of the NSFC and CAS under Contracts Nos. U1232201, U1332201, U1532257, U1532258; CAS under Contracts Nos. KJCX2-YW-N29, KJCX2-YW-N45; 100 Talents Program of CAS; National 1000 Talents Program of China; INPAC and Shanghai Key Laboratory for Particle Physics and Cosmology; German Research Foundation DFG under Contracts Nos. Collaborative Research Center CRC 1044, FOR 2359; Istituto Nazionale di Fisica Nucleare, Italy; Koninklijke Nederlandse Akademie van Wetenschappen (KNAW) under Contract No. 530-4CDP03; Ministry of Development of Turkey under Contract No. DPT2006K-120470; National Science and Technology fund; The Swedish Resarch Council; U.S. Department of Energy under Contracts Nos. DE-FG02-05ER41374, DE-SC-0010118, DE-SC-0010504, DE-SC-0012069; University of Groningen (RuG) and the Helmholtzzentrum fuer Schwerionenforschung GmbH (GSI), Darmstadt; WCU Program of National Research Foundation of Korea under Contract No. R32-2008-000-10155-0.
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