Origin of the low-mass electron pair excess in light nucleus-nucleus collisions
Keywords
electron: pair production, electron: yield, p: spectator, nucleus nucleus: interaction, spectrometer, carbon, p p: inclusive reaction, p deuteron: inclusive reaction, differential cross section: mass dependence, isospin: dependence, bremsstrahlung, Delta(1232)_s16: semileptonic decay, Darmstadt SIS, 1.25 GeV/nucleon Author supplied: Virtual bremsstrahlung, Dileptons, Nucleon-nucleon collisions
Abstract
We report measurements of electron pair production in elementary p_s16p and d_s16p reactions at 1.25 GeV/u with the HADES spectrometer. For the first time, the electron pairs were reconstructed for n_s16p reactions by detecting the proton spectator from the deuteron breakup. We find that the yield of electron pairs with invariant mass Me_s16e- > 0.15 GeV/c2 is about an order of magnitude larger in n_s16p reactions as compared to p_s16p. A comparison to model calculations demonstrates that the production mechanism is not sufficiently described yet. The electron pair spectra measured in C_s16C reactions are compatible with a superposition of elementary n_s16p and p_s16p collisions, leaving little room for additional electron pair sources in such light collision systems.
