Study of baryonic resonances and ρ meson production in the reaction pp → ppπ+π- at 3.5 GeV with HADES

The High Acceptance Di-Electron Spectrometer (HADES) installed at GSI in Darmstadt and de signed to investigate dielectron production in heavy-ion collisions in the range of kinetic beam energies 1-3 A GeV is also an excellent detector for charged hadron detection. We discuss the analysis of the pp → ppπ+π- channel at an incident energy of 3.5 GeV, using results from pp→ppπ0, pp→pnπ+ and pp → pKΛ measured at the same energy by HADES. A consistent description of the differential cross sections as a function of the invariant mass and the production angles is achieved by a simple resonance model taking into account the single and the double excitation of baryonic resonances with masses up to 1.9 GeV. The contributions can be quantified and confronted to the inputs of transport models or to the predictions of dedicated models for nucleon-nucleon reactions. In addition, using specific kinematical cuts, the total production cross section and the angular dis tribution of the ρ meson have been also extracted. As both baryon resonances and the ρ meson are important sources of di-electrons, these results will provide valuable constraints for the interpretation of the dielectron spectra measured by the HADES collaboration.

Partial Wave Analysis of HADES Data for Two-Pion Production in Pion-Nucleon Reactions

Pion beams are important tools to study features of baryonic resonances and their decay channels because resonances are produced in s-channel at fixed mass equal to √s. In 2014 the HADES collaboration has performed systematic measurements in the second resonance region scanning around the mass of the N*(1520). Pion beams at four momenta (0.654, 0.686, 0.738 and 0.787 GeV/c) impinging on polyethylene and carbon targets have been used. With the use of the multichannel Partial Wave Analysis (PWA) the role of the N*(1520) resonance in conjunction with the intermediate ρ-meson production has been studied. Preliminary results at 0.654 GeV/c on exclusive production of two pions (ηπ+π- and pπ-π0) in the final state are presented.

Partial wave analysis of HADES data for two-pion production in pion-nucleon reactions

Pion beams are perfect tools to probe resonance excitations at a fixed energy, thus properties of baryonic resonances and their coupling channels can be studied. The HADES Collaboration performed a systematic scan around the second resonance region at four different pion beam momenta 0.656, 0.69, 0.748 and 0.8 GeV/c in π− p reaction. The role of the N(1520) resonance in conjunction with the intermediate ρ-meson production has been studied in the framework of a partial wave analysis. Preliminary results on exclusive channels with one pion (π− p) and two pions (nπ+π− and pπ−π0) in the final state are presented.

Time-Like Baryon Transitions studies with HADES

The HADES collaboration uses the e+e− production as a probe of the resonance matter produced in collisions at incident energies of 1-3.5 GeV/nucleon at GSI. Elementary reactions provide useful references for these studies and give information on resonance Dalitz decays (R→Ne+e−). Such processes are sensitive to the structure of time-like electromagnetic baryon transitions in a kinematic range where (off-shell) vector mesons play a crucial role. Results obtained in proton-proton reactions and in a commissioning pion-beam experiment are reported and prospects for future pion beam experiments and for first hyperon Dalitz decay measurements are described. The connection with the investigations of medium effects to be continued with HADES in the next years at SIS18 and SIS100 is also discussed.

Partial wave analysis of HADES data for two-pion production in pion-nucleon reactions

Pion beams are perfect tools to probe resonance excitations at a fixed energy, thus properties of baryonic resonances and their coupling channels can be studied. The HADES Collaboration performed a systematic scan around the second resonance region at four different pion beam momenta 0.656, 0.69, 0.748 and 0.8 GeV/c in π− p reaction. The role of the N(1520) resonance in conjunction with the intermediate ρ-meson production has been studied in the framework of a partial wave analysis. Preliminary results on exclusive channels with one pion (π− p) and two pions (nπ+π− and pπ−π0) in the final state are presented.

Subthreshold Ξ− production in proton-nucleus collisions in a BUU model

We study the production of the doubly strange Ξ baryon in subthreshold p + A collisions using a BUU type transport model. We propose a new mechanism for Ξ creation in a two-step process via hyperon-nucleon collisions. We study the influence of the anisotropy of hyperon production in N + N collisions on the Ξ multiplicity. Applying reasonable assumptions on the unknown elementary cross sections, we are able to reconstruct the Ξ yield observed by the HADES collaboration (GSI, Darmstadt) in subthreshold p+Nb collisions.

Lambda - Proton Correlation in Pion-Induced Reactions at 1.7 GeV/c

World data on Λ – p scattering in pion-induced redactions are quite scare. In 2014 the HADES Collaboration performed an experiment campaign with pionnucleon reactions π¯ + A (A = C,W) at 1.7 GeV/c. Hereby, the exclusive channel π¯ + p → K0 + Λ (Λ + p → Λ + p) may provide information on Λ proton scattering and moreover shed light on the short range interaction using dedicated simulations for comparison. The on-going analysis of the exclusive channel with especial emphasis on the event selection is outlined.