Observation of an Isoscalar Resonance with Exotic J(PC)=1(-+) Quantum Numbers in J/psi -> gamma eta eta '

Using a sample of (10.09 +/- 0.04) x 10(9) J/psi events collected with the BESIII detector operating at the BEPCII storage ring, a partial wave analysis of the decay J/psi -> gamma eta eta ' is performed. The first observation of an isoscalar state with exotic quantum numbers J(PC) = 1(-+), denoted as eta(1) (1855), is reported in the process J/psi -> gamma eta(1) (1855) with eta(1) (1855) -> eta eta '. Its mass and width are measured to be (1855 +/- 9(-1)(+6) MeV/c(2) 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 19 sigma.

Automated summary

This study observed the decay process of J/psi -> gamma eta eta' and discovered a new isoscalar state with exotic quantum numbers, eta(1) (1855), with measured mass and width.