Σ0 production in proton nucleus collisions near threshold

Abstract The production of Σ 0 baryons in the nuclear reaction p (3.5 GeV) + Nb (corresponding to s N N = 3.18 GeV) is studied with the detector set-up HADES at GSI, Darmstadt. Σ 0 s were identified via the decay Σ 0 → Λ γ with subsequent decays Λ → p π − in coincidence with a e + e − pair from either external ( γ → e + e − ) or internal (Dalitz decay γ ⁎ → e + e − ) gamma conversions. The differential Σ 0 cross section integrated over the detector acceptance, i.e. the rapidity interval 0.5 y 1.1 , has been extracted as Δ σ Σ 0 = 2.3 ± ( 0.2 ) s t a t ± ( − 0.6 + 0.6 ) s y s ± ( 0.2 ) n o r m mb, yielding the inclusive production cross section in full phase space σ Σ 0 t o t a l = 5.8 ± ( 0.5 ) s t a t ± ( − 1.4 + 1.4 ) s y s ± ( 0.6 ) n o r m ± ( 1.7 ) e x t r a p o l mb by averaging over different extrapolation methods. The Λ a l l / Σ 0 ratio within the HADES acceptance is equal to 2.3 ± ( 0.2 ) s t a t ± ( − 0.6 + 0.6 ) s y s . The obtained rapidity and momentum distributions are compared to transport model calculations. The Σ 0 yield agrees with the statistical model of particle production in nuclear reactions.