We report the observation and study of the decay J/ψ→φηη′ using 1.3×109 J/ψ events collected with the BESIII detector. Its branching fraction, including all possible intermediate states, is measured to be (2.32±0.06±0.16)×10-4. We also report evidence for a structure, denoted as X, in the φη′ mass spectrum in the 2.0-2.1 GeV/c2 region. Using two decay modes of the η′ meson (γπ+π- and ηπ+π-), a simultaneous fit to the φη′ mass spectra is performed. Assuming the quantum numbers of the X to be JP=1-, its significance is found to be 4.4σ, with a mass and width of (2002.1±27.5±21.4) MeV/c2 and (129±17±9) MeV, respectively, and a product branching fraction B(J/ψ→ηX)×B(X→φη′)=(9.8±1.2±1.7)×10-5. Alternatively, assuming JP=1+, the significance is 3.8σ, with a mass and width of (2062.8±13.1±7.2) MeV/c2 and (177±36±35) MeV, respectively, and a product branching fraction B(J/ψ→ηX)×B(X→φη′)=(9.6±1.4±2.0)×10-5. The angular distribution of J/ψ→ηX is studied and the two JP assumptions of the X cannot be clearly distinguished due to the limited statistics. In all measurements the first uncertainties are statistical and the second systematic.
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. 11335008, No. 11425524, No. 11625523, No. 11635010, and No. 11735014; the Chinese Academy of Sciences (CAS) Large-Scale Scientific Facility Program; the CAS Center for Excellence in Particle Physics (CCEPP); Joint Large-Scale Scientific Facility Funds of the NSFC and CAS under Contracts No. U1532257, No. U1532258 and No. U1832207; CAS Key Research Program of Frontier Sciences under Contracts No. QYZDJ-SSW-SLH003 and No. QYZDJ-SSW-SLH040; 100 Talents Program of CAS; the Institute of Nuclear and Particle Physics and Shanghai Key Laboratory for Particle Physics and Cosmology; German Research Foundation DFG under Contracts No. Collaborative Research Center CRC 1044, No. 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 Research Council; U.S. Department of Energy under Contracts No. DE-FG02-05ER41374, No. DE-SC-0010118, No. DE-SC-0010504, and No. DE-SC-0012069; University of Groningen (RuG) and the Helmholtzzentrum fuer Schwerionenforschung GmbH (GSI) Darmstadt; and Institute for Basic Science (Korea) under project code IBS-R016-D1.