Search

The aim of the present analysis is to determine the relative production cross sections of the Λ(1405) and Σ(1385) resonances in p+p collisions at E = 3.5 GeV measured with HADES. Upper and lower limits have been determined for the ratio $\sigma_{(\Sigma(1385)^{0}+p+K^{+})}/\sigma_{(\Lambda(1405)+p+K^{+})}=0.76_{-0.26}^{+0.54}$. 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) signals is not possible. [ABSTRACT FROM AUTHOR]

With the HADES spectrometer at GSI we have studied dilepton production in various collision systems from elementary N+N, over p+A, up to the medium-heavy Ar+KCl system. We have confirmed the puzzling results of the former DLS collaboration at the Bevalac. While we have traced the origin of the excess pair yield in C+C collisions to elementary p+p and n+p processes, we find a significant contribution from the dense phase of the collision in larger Ar+KCl system. From recently obtained e+e- pair spectra in p+p and p+Nb interactions at 3.5 GeV kinetic beam energy the inclusive production cross sections for neutral pions, η , ω and ρ mesons are extracted for the first time at this beam energy. Furthermore, the production mechanisms of the vector mesons, which are not known at these energies, are investigated. The direct comparison of p+p and p+Nb data allows us to investigate in-medium mass modifications of vector mesons at nuclear ground state density. On the other hand, exclusive production of ω and η mesons in p+p reactions at 3.5 GeV were studied via their π+π-π0 decay channel. Production cross sections and angular distributions for both states were determined. [ABSTRACT FROM AUTHOR]

We present results on the K*(892)+ production in proton-proton collisions at a beam energy of E = 3.5 GeV, which is hitherto the lowest energy at which this mesonic resonance has been observed in nucleon-nucleon reactions. The data are interpreted within a two-channel model that includes the 3-body production of K*(892)+ associated with the Lambda- or Sigma-hyperon. The relative contributions of both channels are estimated. Besides the total cross section sigma(p+p→K*(892)++X) = 9.5 +- 0.9 +1.1-0.9±0.7 μub, that adds a new data point to the excitation function of the K*(892)+ production in the region of low excess energy, transverse momenta and angular spectra are extracted and compared with the predictions of the two-channel model. The spin characteristics of K*(892)+ are discussed as well in terms of the spin-alignment. [ABSTRACT FROM AUTHOR]

An exclusive analysis of the four-body final states +p+p++Ko and So+p+p++Ko measured with HADES for p+p collisions at a beam kinetic energy of 3.5 GeV is presented. The analysis uses various phase space variables, such as missing mass and invariant mass distributions, in the four-particle event selection (p,p+,p+,p-) to find cross sections of the different production channels, contributions of the intermediate resonances ++ and S(1385)+, and corresponding angular distributions. A dominant resonant production is seen, where the reaction ++++K0 has a cross section about ten times higher (29.45±0.08+1.67-1.46±2.06µb) than the analogous nonresonant reaction (2.57±0.02+0.21-1.98±0.18µb). A similar result is obtained in the corresponding S0 channels with 9.26±0.05+1.41-0.31±0.65µb in the resonant and 1.35±0.02+0.10-1.35±0.09µb in the nonresonant reactions [ABSTRACT FROM AUTHOR]