Probing hadronic polarizations with dilepton anisotropies

We investigate the production of e ⁺ e ^? pairs from p + Be and nucleus-nucleus collisions from 2 GeV/A to 200 GeV/A within a covariant transport approach and focus on the dilepton angular anisotropies as a function of the dilepton invariant mass. Whereas the low mass regime yields information about the Dalitz decays of the Δ, η and ω, above M ≈ 0.5 GeV the angular anisotropies provide additional information about the π ⁺ π ^? → ρ ⁰ → e ⁺ e ^? channel in the medium. The anisotropy coefficient is found to change its sign for M > 0.5 GeV in case of nucleus-nucleus reactions when increasing the bombarding energy from 2 GeV/A to 200 GeV/A which sheds some light on the ππ → ρ dynamics.