$Sigma^0$ production in proton nucleus collisions near threshold

The production of $Sigma^{0}$ baryons in the nuclear reaction p (3.5 GeV) + Nb (corresponding to $sqrt{s_{NN}}=3.18$ GeV) is studied with the detector set-up HADES at GSI, Darmstadt. $Sigma^{0}$s were identified via the decay $Sigma^{0} rightarrow Lambda gamma$ with subsequent decays $Lambda rightarrow p pi^{-}$ in coincidence with a $e^{+}e^{-}$ pair from either external ($gamma rightarrow e^{+} e^{-}$) or internal (Dalitz decay $gamma^{*}rightarrow e^{+} e^{-}$) gamma