Confirmation of the 1 - + meson exotics in the η π 0 system

Abstract The exclusive reaction π − p → η π 0 n , η → π + π − π 0 at 18 GeV / c has been studied with a partial wave analysis on a sample of 23 492 η π 0 n events from BNL experiment E852. A mass-dependent fit is consistent with a resonant hypothesis for the P + wave, thus providing evidence for a neutral exotic meson with J P C = 1 − + , a mass of 1257 ± 20 ± 25 MeV / c 2 , and a width of 354 ± 64 ± 60 MeV / c 2 . New interpretations of the meson exotics in neutral η π 0 system observed in E852 and Crystal Barrel experiments are discussed.