We report on measurements of low-mass electron pairs in 450 GeV p-Be, p-Au, and 200 GeV/nucleon S-Au collisions at central rapidities. For the proton induced interactions, the low-mass spectra are, within the systematic errors, satisfactorily explained by electron pairs from hadron decays, whereas in the S-Au system an enhancement over the hadronic contributions by a factor of 5.0±0.7(stat)±2.0(syst) in the invariant mass range 0.2<m<1.5GeV/c2 is observed. The properties of the excess suggest that it arises from two-pion annihilation ππ→e+e−.
CENTRAL EVENTS.
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A search for direct electron pairs was performed at the 6.4 TeV 32 S emulsion interactions at CERN. A total of 81 directly produced electron pairs have been observed, with an average number per interaction of about two. The results have been analysed in the light of the predictions of quantum electrodynamical calculations. A simple interpretation for the extracted results based on the virtual mass distribution is presented. The experimental results are in partial agreement with the present theories. The virtual mass distribution does not show a 1/m behaviour.
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