Observation and study of the decay $J/\psi\rightarrow\phi\eta\eta'$

Abstract

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.