Observation of an Isoscalar Resonance with Exotic JPC=1-+ Quantum Numbers in J /ψ →γηη′

Abstract

Using a sample of (10.09±0.04)×109 J/ψ events collected with the BESIII detector operating at the BEPCII storage ring, a partial wave analysis of the decay J/ψ→γηη′ is performed. The first observation of an isoscalar state with exotic quantum numbers JPC=1-+, denoted as η1(1855), is reported in the process J/ψ→γη1(1855) with η1(1855)→ηη′. Its mass and width are measured to be (1855±9-1+6) MeV/c2 and (188±18-8+3) MeV, respectively, where the first uncertainties are statistical and the second are systematic, and its statistical significance is estimated to be larger than 19σ.