A search for radiative decays of the P-wave spin singlet charmonium resonance hc is performed based on 4.48×108 ψ′ events collected with the BESIII detector operating at the BEPCII storage ring. Events of the reaction channels hc→γη′ and γη are observed with a statistical significance of 8.4σ and 4.0σ, respectively, for the first time. The branching fractions of hc→γη′ and hc→γη are measured to be B(hc→γη′)=(1.52±0.27±0.29)×10-3 and B(hc→γη)=(4.7±1.5±1.4)×10-4, respectively, where the first errors are statistical and the second are systematic uncertainties.
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 No.11125525, No.11235011, No.11322544, No.11335008, No.11425524, No.11521505, No.Y61137005C; 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 No.11179007, No.U1232201, No.U1332201; CAS under Contracts No.KJCX2-YW-N29, No.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 Contract No.Collaborative Research Center CRC-1044; 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; Russian Foundation for Basic Research under Contract No.14-07-91152; The Swedish Resarch Council; U.S. Department of Energy under Contracts No.DE-FG02-05ER41374, No.DE-SC-0010504, No.DE-SC0012069, No.DESC0010118; U.S. National Science Foundation; 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.