Exotic ηπ state in annihilation at rest into π−π0η pspectator

Abstract With antiprotons stopped in liquid deuterium, the p n annihilation channel π − π 0 η was studied using a final sample of 52 576 events obtained for a spectator proton momentum ηπ P-wave is clearly apparent by its interferences with the dominant ρ − (770) and a 2 (1320) two-meson resonances. A partial wave analysis of the data yields evidence for resonant behaviour of the ηπ P-wave, which has the non- q q quantum numbers I G =1 − , J PC =1 −+ . The extracted Breit-Wigner resonance parameters are m =(1400±20±20) MeV/c 2 and Γ =(310±50 +50 −30 ) MeV/c 2 .