Origin of the low-mass electron pair excess in light nucleus-nucleus collisions

We report measurements of electron pair production in elementary p+p and d+p reactions at 1.25 GeV/u with the HADES spectrometer. For the first time, the electron pairs were reconstructed for n+p reactions by detecting the proton spectator from the deuteron breakup. We find that the yield of electron pairs with invariant mass Me+e−>0.15 GeV/c2 is about an order of magnitude larger in n+p reactions as compared to p+p . A comparison to model calculations demonstrates that the production mechanism is not sufficiently described yet. The electron pair spectra measured in C+C reactions are compatible with a superposition of elementary n+p and p+p collisions, leaving little room for additional electron pair sources in such light collision systems.

Note:

11 pages, 2 figures, \usepackage{epsfig}

13.40.Hq
25.75.Dw
25.75.-q
Virtual bremsstrahlung
Dileptons
Nucleon-nucleon collisions
Nucleon–nucleon collisions
electron: pair production
electron: yield
p: spectator

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Figures(2)

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