Search for neutral bosons in relativistic heavy-ion collisions

In this talk, I will describe results on 1,220 electron pairs produced from a ²⁰⁷Pb beam at 160A GeV in a nuclear experiment EMU 11 conducted at the CERN SPS. These electron pairs were produced at a distance of more than 50 μm from the primary interactions, which eliminates contamination due to Dalitz pairs. Results on electron pairs with invariant mass Q ranging between 1 and 100 MeV and life-time τ between 10⁻¹⁵ s and 10⁻¹² s were analyzed. After subtracting background pairs from the materialization of photons and from the decays of π₀ to photons from the data, they exhibit an enhancement at low mass Q = 6 – 20 MeV with narrow peaks at 7 ± 1 MeV, 19 ± 1 MeV and τ ≤ 10⁻¹³s. (author)