Dielectron production in Ar_s16KCl collisions at 1.76A GeV
Keywords
INSPIRE: threshold, nuclear matter: effect, omega(783), heavy ion: scattering, argon, potassium: chlorine, electron: pair production, electron positron: mass spectrum, dilepton: yield, vector meson: yield, mass spectrum: transverse, angular distribution, helicity, rapidity spectrum, HADES, experimental results, Darmstadt SIS, 1.76 GeV/nucleon
Abstract
We present results on dielectron production in Ar_s16KCl collisions at 1.76A GeV. For the first time $omega$ mesons could be reconstructed in a heavy-ion reaction at a bombarding energy which is well below the production threshold in free nucleon-nucleon collisions. The omega multiplicity has been extracted and compared to the yields of other particles, in particular of the phi meson. At intermediate e_s16e- invariant masses, we find a strong enhancement of the pair yield over a reference spectrum from elementary nucleon-nucleon reactions suggesting the onset of non-trivial effects of the nuclear medium. Transverse-mass spectra and angular distributions have been reconstructed in three invariant mass bins. In the former unexpectedly large slopes are found for high-mass pairs. The latter, in particular the helicity-angle distributions, are largely consistent with expectations for a pair cocktail dominated at intermediate masses by delta Dalitz decays.
