Search for Structure in the Nucleon Isobar Mass Spectrum from 1100 to 1800 MeV

A new high-resolution (±5 MeV) missing-mass spectrometer was used to search for minor peaks and structure in the $N^{*}$ spectrum with ∼${10}^5$ events per 2-MeV mass bin. All the widths were found to be narrower than widths obtained from $\pi p$ phase-shift analyses. For example, our result for $N^{*}\mathrm{}\left(1512\right)\mathrm{}$ is $\Gamma =88\mathrm{}\pm 2$ MeV as compared with the "table value" of 105-155 MeV. No narrow structure greater than 5% of the cross section for the known peaks was observed.