Dielectron production in Ar+KCl collisions at 1.76A GeV

Understand

We present results on dielectron production in Ar+KCl 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+e- 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.