Observation of the electromagnetic doubly OZI-suppressed decay J /ψ →φπ0

Using a sample of 1.31 billion J/ψ events accumulated with the BESIII detector at the BEPCII collider, we report the observation of the decay J/ψ→φπ0, which is the first evidence for a doubly Okubo-Zweig-Iizuka suppressed electromagnetic J/ψ decay. A clear structure is observed in the K+K- mass spectrum around 1.02 GeV/c2, which can be attributed to interference between J/ψ→φπ0 and J/ψ→K+K-π0 decays. Due to this interference, two possible solutions are found. The corresponding measured values of the branching fraction of J/ψ→φπ0 are [2.94±0.16(stat)±0.16(syst)]×10-6 and [1.24±0.33(stat)±0.30(syst)]×10-7.