The aim of the present analysis is to determine the relative production cross sections of the Λ(1405) and Σ(1385)0 resonances in p+p collisions at Ekin = 3.5 GeV measured with HADES. Upper and lower ...limits have been determined for the ratio \documentclass12pt{minimal}
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\begin{document}$\sigma_{(\Sigma(1385)^{0}+p+K^{+})}/\sigma_{(\Lambda(1405)+p+K^{+})}=0.76_{-0.26}^{+0.54}$\end{document}. The knowledge of this ratio is an essential input for the analysis of the decay Λ(1405)→Σ±π ∓ , where an unambiguous separation of the Λ(1405) and Σ(1385)0 signals is not possible.
e+e− production was studied using the High Acceptance DiElectron Spectrometer (HADES). In pp collisions at 2.2 GeV kinetic beam energy, the exclusive η production and the Dalitz decay η → γe+e− have ...been reconstructed. The electromagnetic form factor of the latter decay was found to be in good agreement with the existing theoretical predictions. In addition, an inclusive e+e− invariant-mass spectrum from the 12C + 12C reaction at 2 AGeV is presented and compared with a simplified thermal model.
The tagged quasi-free np→npπ+π−np→npπ+π− reaction has been studied experimentally with the High Acceptance Di-Electron Spectrometer (HADES) at GSI at a deuteron incident beam energy of 1.25 ...GeV/nucleon (View the MathML sources∼2.42 GeV/c for the quasi-free collision). For the first time, differential distributions of solid statistics for π+π−π+π− production in np collisions have been collected in the region corresponding to the large transverse momenta of the secondary particles. The invariant mass and angular distributions for the np→npπ+π−np→npπ+π− reaction are compared with different models. This comparison confirms the dominance of the t -channel with ΔΔ contribution. It also validates the changes previously introduced in the Valencia model to describe two-pion production data in other isospin channels, although some deviations are observed, especially for the π+π−π+π− invariant mass spectrum. The extracted total cross section is also in much better agreement with this model. Our new measurement puts useful constraints for the existence of the conjectured dibaryon resonance at mass M∼2.38 GeVM∼2.38 GeV and with width Γ∼70 MeVΓ∼70 MeV.
The emission of e+e− pairs from C+C collisions at an incident energy of 1 GeV per nucleon has been investigated. The measured production probabilities, spanning from the π0-Dalitz to the ρ/ω ...invariant-mass region, display a strong excess above the cocktail of standard hadronic sources. The bombarding-energy dependence of this excess is found to scale like pion production, rather than like eta production. The data are in good agreement with results obtained in the former DLS experiment.
The High Acceptance DiElectron Spectrometer HADES has been recently commissioned at GSI, Darmstadt. It has been designed for systematic studies of hadron properties inside nuclear matter. We report ...first preliminary results on invariant masses e+e--pairs which were measured in 12C + 12C collisions at Ekin=2 GeVdot operatorA. The analysis methods are briefly outlined and a comparison with detailed Monte-Carlo simulations is shown.
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