Search for neutral baryon resonances below pion threshold

The reaction ${p(e,e}^{\prime }{\pi }^{+}{)X}^0$ was studied with two high-resolution magnetic spectrometers to search for narrow baryon resonances. A missing mass resolution of 2.0 MeV was achieved. A search for structures in the mass region of $0.97<\mathrm{}{M}_{X^0}<1.06\mathrm{}$ GeV yielded no significant signal. The yield ratio of ${p(e,e}^{\prime }{\pi }^{+}{)X}^0{/p(e,e}^{\prime }{\pi }^{+})n$ was determined to be $(-0.35\pm 0.35)\times {10}^{-3}$ at 1.004 GeV and $(0.34\mathrm{}\pm 0.42)\times {10}^{-3}$ at 1.044 GeV. This measurement clearly demonstrated the potential of high-resolution missing mass searches in coincidence experiments.