On the momentum correlation of (e+e−) pairs observed in U + U and U + Pb collisions

Abstract First results on the energy and angular dependence of the (e + e − ) pairs, emitted from U + U and U + Pb collisions at a beam energy of 5.9 MeV/u, are presented. The (e + e − ) coincidence measurements were carried out utilizing a double-Orange s-spectrometer, which allows to determine the momentum vectors of the positrons and electrons and, hence, their opening angle θ e + e − . The (e + e − ) sum-energy spectrum obtained for θ e + e − =(180±20)°, which is equivalent to an invariant mass spectrum, indicates multiple-line structures in the energy range between 500 keV and 950 keV for both collision systems. The most pronounced line appears at a sum energy of ∼ 810 keV, corresponding to an invariant mass of ∼ 1.83 MeV / c 2 . No evidence for line structures was found for angles 40° ⩽ θ e + e − ⩽ 170°. The energies of the lines are consistent with our previous observations in the single p positron spectra.