Probing chiral symmetry of nucleon by threshold $\eta \pi$ production
  Double meson production of the eta and pion at the threshold region is investigated in order to determine chiral property of the nucleon.   The eta can be used as a probe for the negative parity nucleon $N^* \equiv N^*(1535)$ produced in the intermediate state.   The coupling of the low energy pion in the final state is then used to extract the sign of the Yukawa coupling, $\gpRR$, which distinguishes the two realizations of chiral symmetry, either naive or mirror, for the nucleon. 
Daisuke Jido, Atsushi Hosaka and Makoto Oka