Search for Narrow Nucleon Resonances below Pion Threshold in the H(E,E ' Pi(+))X and H-2(E,E ' P)X Reactions

In two series of high-resolution coincidence experiments at the three-spectrometer facility at MAMI, the H(e,e' pi(+)) X and H-2(e,e' p) X reactions were studied to search for narrow nucleon resonances below pion threshold. The missing-mass resolution was 0.6-1.6 MeV/c(2) full width at half maximum in the proton experiment and 0.9-1.3 MeV/c(2) in the deuteron experiment. The experiments covered the missing-mass region from the neutron mass up to about 1050 and 1100 MeV/c(2), respectively. None of our measurements showed a signal for narrow resonances to a level of down to 10(-4) with respect to the neutron peak in the missing-mass spectra.