$\Sigma^{0}$ identification in proton induced reactions on a nuclear target

Abstract

We have studied the production of neutral Σ 0 baryons in the reaction p+Nb at an incident proton energy of E kin = 3.5 GeV. The measurement has been performed with the HADES spectrometer at GSI, Darmstadt. Σ 0 → Λ 0 γ and Σ 0 → Λe + e − decays were identified via the charged decay Λ → pπ − coincident to e + e − pairs from external or internal gamma conversion. A total of net 220 Σ 0 candidates has been extracted. We present here the analysis method and the signal verification in simulations.

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

“…For this reason, dielectrons have been identified by requiring two RICH rings, at least one fully reconstructed e ± track and one neighbouring incomplete tracklet detected in front of the magnetic field in the first two MDCs. The missing momentum of the incomplete tracklet has been estimated by applying a most probable hypothesis as described in detail in [29] which partly exploits results and constraints from kinematically similar π 0 Dalitz decays. In this way, the observed incomplete dielectrons are combined into most probable photon signals with a resolution of δE γ (FWHM) = 57 ± 2 MeV [29].…”

“…The missing momentum of the incomplete tracklet has been estimated by applying a most probable hypothesis as described in detail in [29] which partly exploits results and constraints from kinematically similar π 0 Dalitz decays. In this way, the observed incomplete dielectrons are combined into most probable photon signals with a resolution of δE γ (FWHM) = 57 ± 2 MeV [29].…”

“…After weighting and normalisation, both methods lead to the same background yield within 10%. The side band samples used to construct the pπ − background are combined with the reconstructed e ± pairs to obtain the background to the Σ 0 candidates (for details see [29]). The inclusive four-particle pπ − e ± invariant mass distribution is shown in the inset of Fig.…”