J.L. Boyard

Dielectron production in Ar+KCl collisions at 1.76A GeV

We present results on dielectron production in 40 Ar+KCl collisions at 1.76A GeV. For the first time ω mesons could be reconstructed in a heavy-ion reaction at a bombarding energy which is well below the production threshold in free nucleon-nucleon collisions. The ω multiplicity has been extracted and compared to the yields of other particles, in particular of the φ meson. At intermediate e + e invariant masses, we find a strong enhancement of the pair yield over a reference spectrum from elementary nucleon-nucleon reactions suggesting the onset of non-trivial effects of the nuclear medium. Transverse-mass spectra and angular distributions have been reconstructed in three invariant mass bins. In the former unexpectedly large slopes are found for high-mass pairs. The latter, in particular the helicity-angle distributions, are largely consistent with expectations for ]

Inclusive dielectron production in proton-proton collisions at 2.2 GeV beam energy

Data on inclusive dielectron production are presented for the reaction p+p at 2.2 GeV measured with the High Acceptance DiElectron Spectrometer (HADES). Our results supplement data obtained earlier in this bombarding energy regime by DLS and HADES. The comparison with the 2.09 GeV DLS data is discussed. The reconstructed e+e- distributions are confronted with simulated pair cocktails, revealing an excess yield at invariant masses around 0.5 GeV/c2. Inclusive cross sections of neutral pion and eta production are obtained.

Medium effects in proton-induced

We present the analysis of the inclusive K 0 production in p + p and p + Nb collisions measured with the HADES detector (GSI Helmholtzzentrum for Heavy-Ion Research, Darmstadt) at a beam kinetic energy of 3.5 GeV. Data are compared to the Giessen Boltzmann-Uehling-Uhlenbeck (GiBUU) transport model. The data suggest the presence of a repulsive momentum-dependent kaon potential as predicted by the chiral perturbation theory (ChPT). For the kaon at rest and at normal nuclear density, the ChPT potential amounts to ≈ 35 MeV. A detailed tuning of the kaon production cross sections implemented in the model has been carried out to reproduce the experimental data measured in p + p collisions. The uncertainties in the parameters of the model were examined with respect to the sensitivity of the experimental results from p + Nb collisions to the in-medium kaon potential.

K^{0}

Abstract An experimental study of the 3 He( γ , π + ) 3 H reaction has been performed in the region of the Δ 1236 resonance between 227 MeV and 453 MeV. The experiment shows two main features: at fixed four-momentum transfer q 2 , the resonance is shifted towards lower energies, this shift increasing with q 2 ; at a fixed angle, but variable q 2 , the minimum of the charge form factor observed in the elastic scattering of electrons on 3 He does not appear. Recent calculations explain partly these two effects. This experiment might be used as part of a test of time-reversal invariance in the electromagnetic interaction of hadrons.

production at 3.5 GeV

An exclusive analysis of the 4-body final states

Coherent π+ photoproduction on 3He in the region of the Δ1236 resonance

\mathrm{\Lambda + p + \pi^{+} + K^{0}}

Associate K^0 production in p+p collisions at 3.5 GeV: The role of Delta(1232)++

and

Inclusive pion and η production in p+Nb collisions at 3.5 GeV beam energy

\mathrm{\Sigma^{0} + p + \pi^{+} + K^{0}}

Quasi-free (p, pα) scattering on 24Mg, 28Si, 40Ca and 58Ni at 157 MeV

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,

Subthreshold Ξ^{-} production in collisions of p(3.5 GeV)+Nb.

\pi^+