Experiments on Low Energy Bhabha Scattering Search for Neutral Resonances in the MeV/c² Mass Region

Abstract

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 [1–3]. As summarized in the previous contribution [4], 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 [5]. 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 (or, in the excitation function for anihilation-in-flight) [6–22]. For the sake of clarity, the list of references is restricted to experimental works only, already published or submitted for publication.