Sensitive search for resonances in low-energy e+e- scattering

We have searched for resonances in e+e- scattering in a range of positron kinetic energies from 1.9 to 2.5 MeV (1.75-1.88 MeV invariant energy). Such resonances would exist if the anomalous electron-positron pairs observed in heavy-ion collisions were due to two-body decay of a neutral object. Our 97% confidence limit excludes resonances with an energy-integrated cross section greater than 0.3 to 2.4 beV/sr, depending upon the incident positron energy. For scalar resonances, this corresponds to a lower limit on the lifetime that varies from 8 × 10-14 to 5 × 10-13 sec. These are the most sensitive limits to date.