Confirmation of a pi_1^0 Exotic Meson in the \eta \pi^0 System

TL;DR

This study provides evidence for a neutral exotic meson with quantum numbers $J^{PC} = 1^{-+}$ in the $ar{ ext{eta}} ext{pi}^0$ system, based on partial wave analysis of high-energy pion-proton reactions.

Contribution

First experimental confirmation of a neutral $1^{-+}$ exotic meson in the $ar{ ext{eta}} ext{pi}^0$ system using partial wave analysis.

Findings

Evidence for a $J^{PC} = 1^{-+}$ meson at 1257 MeV/c^2

Measured width of the meson as 354 MeV/c^2

Consistent with previous observations in other experiments

Abstract

The exclusive reaction $\pi^- p \to \eta \pi^0 n$, $\eta \to \pi^+ \pi^- \pi^0$ at 18 GeV$/c$ has been studied with a partial wave analysis on a sample of 23~492 $\eta \pi^0 n$ 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 $\eta \pi^0$ system observed in E852 and Crystal Barrel experiments are discussed.