Confirmation of a pi_1^0 Exotic Meson in the ηπ^0 System

Abstract

The exclusive reaction $π^- p \to ηπ^0 n$, $η\to π^+ π^- π^0$ at 18 GeV$/c$ has been studied with a partial wave analysis on a sample of 23~492 $ηπ^0 n$ 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 $J^{PC} = 1^{-+}$, a mass of $1257 \pm 20 \pm 25$ MeV$/c^2$, and a width of $354 \pm 64 \pm 60$ MeV$/c^2$. New interpretations of the meson exotics in neutral $ηπ^0$ system observed in E852 and Crystal Barrel experiments are discussed.