Experiments on low energy Bhabha scattering - search for neutral resonances in the MeV/c2 mass region

In the last years, a series of experiments on low-energy Bhabha scattering was prompted by the evidence for correlated back-to-back e+e- emission, found in heavy-ion experiments, several monoenergetic e+e- pairs, with sharp sum energies between 500 keV and 815 keV, were observed. Also reported was the detection of correlated back-to-back emission of two γ-quanta with a sum energy of 1062 keV. One is led to conclude that one deals with the decay of various excited states of a composite extended object with internal structure into e+e- or γγ-pairs. Bearing this in mind, numerous experimental groups addressed themselves to the question of whether such a hypothetical e+e- object could be created in e+e- collisions and whether it would manifest its eventual decay as a resonance in the excitation function for Bhabha scattering. (orig./HSI)