Search for e+e− pairs with narrow sum-energy distributions in heavy-ion collisions

Abstract The investigation of e + e − pairs emitted in heavy-ion collisions at the Coulomb barrier has been continued at GSI Darmstadt with the redesigned spectrometer EPoS II. Due to its enlarged efficiency for the detection of e + e − pairs the reproducibility of the narrow line structures previously observed in the e + e − sum-energy spectra with the EPOS I spectrometer could be tested using a highly improved statistical database. No lines have been observed with the new data sets when applying the same selection criteria as in the old data. Our measurements give upper limits for the cross-sections of these lines, which are a factor of up to 10 smaller than the cross-sections deduced from the EPOS I data.