Search for narrow nucleon resonances below pion threshold in the H(e,e'π+)X and 2H(e,e'p)X reactions

In two series of high-resolution coincidence experiments at the three-spectrometer facility at MAMI, the H(e,e'π⁺)X and ²H(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/c² full width at half maximum in the proton experiment and 0.9 1.3 MeV/c² in the deuteron experiment. The experiments covered the missing-mass region from the neutron mass up to about 1050 and 1100 MeV/c², 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.