Status of Nucleon Resonances with Masses $M<M_N+M_π$

Abstract

We discuss different interpretations of peaks observed a few years ago by Tatischeff et al. in missing mass spectra of the reaction $pp->pi^+pX$, which were declared as new exited nucleon states with small masses. A study of the possible production of such states in the process $γp->pi^+N^*->pi^+ +γγn$ by analyzing the invariant mass spectrum of $γγn$ is proposed. It is shown that the data, obtained recently at MAMI-B, can allow to analyze this process and to get information about an existence of exited nucleon states with small masses.