Partial wave analysis of J/ψ →γη η

Using a sample of (10.09±0.04)×109 J/ψ events collected with the BESIII detector, a partial wave analysis of J/ψ→γη η is performed. The masses and widths of the observed resonances and their branching fractions are reported. The main contribution is from J/ψ→γf0(2020) with f0(2020)→η η , which is found with a significance of greater than 25σ. The product branching fraction B(J/ψ→γf0(2020)) B(f0(2020)→η η ) is measured to be (2.63±0.06(stat.)+0.31-0.46(syst.))×10-4