HADES is a secondary generation experiment operated at GSI Darmstadt with the main goal to study dielectron production in proton, pion and heavy ion induced reactions. The first part of the HADES ...mission is to reinvestigate the puzzling pair excess measured by the DLS collaboration in C+C and Ca+Ca collisions at 1A GeV. For this purpose dedicated measurements with the C+C system at 1 and 2A GeV were performed. The pair excess above a cocktail of free hadronic decays has been extracted and compared to the one measured by DLS. Furthermore, the excess is confronted with predictions of various model calculations.
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 E
kin
= 3.5 GeV measured with HADES. Upper and ...lower limits have been determined for the ratio
. 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.
We report on recent data of e+e− pair emission in proton nucleus collisions at energies above the light vector meson production thresholds. Invariant mass distributions for the p+Nb system at Ekin ...3.5 GeV are compared to data from elementary p+p reactions at the same beam energy. We observe a constant π0/ω yield ratio for both systems but an excess in the mass region above the π0 mass. Furthermore we present here the normalization procedure that was applied to p+Nb collisions by measuring the production of negative pions in the HADES acceptance.
We present an analysis of the Lambda(1405) resonance produced in the reaction p+p->Sigma^{pm}+pi^{mp}+K+p at 3.5 GeV kinetic beam energy measured with HADES at GSI. The two charged decay channels ...Lambda(1405) -> Sigma^{\pm}+pi^{\mp} have been reconstructed for the first time in p+p collisions. The efficiency and acceptance-corrected spectral shapes show a peak position clearly below 1400 MeV/c^2. We find a total production cross section of sigma_{Lambda(1405)}=9.2 +- 0.9 +- 0.7 +3.3-1.0 mub. The analysis of its polar angle distribution suggests that the Lambda(1405) is produced isotropically in the p-p center of mass system.
We have developed a versatile software package for the simulation of di-electron production in \(pp\) and \(dp\) collisions at SIS energies. Particular attention has been paid to incorporate ...different descriptions of the Dalitz decay \(\Delta \to N e^+e^-\) via a common interface. In addition, suitable parameterizations for the virtual bremsstrahlung process \(NN \to NN e^+e^-\) based on one-boson exchange models have been implemented. Such simulation tools with high flexibility of the framework are important for the interpretation of the di-electron data taken with the HADES spectrometer and the design of forthcoming experiments.
We present data on dielectron emission in proton induced reactions on a Nb target at 3.5 GeV kinetic beam energy measured with HADES installed at GSI. The data represent the first high statistics ...measurement of proton-induced dielectron radiation from cold nuclear matter in a kinematic regime, where strong medium effects are expected. Combined with the good mass resolution of 2%, it is the first measurement sensitive to changes of the spectral functions of vector mesons, as predicted by models for hadrons at rest or small relative momenta. Comparing the e+e invariant mass spectra to elementary p+p data, we observe for e+e momenta Pee < 0.8 GeV/c a strong modification of the shape of the spectrum, which we attribute to an additional rho-like contribution and a decrease of omega yield. These opposite trends are tentatively interpreted as a strong coupling of the rho meson to baryonic resonances and an absorption of the omega meson, which are two aspects of in-medium modification of vector mesons.
We present the transverse momentum spectra and rapidity distributions of {pi}{sup -} and K{sub S}{sup 0} in Ar + KCl reactions at a beam kinetic energy of 1.756 A GeV measured with the High ...Acceptance Di-Electron Spectrometer (HADES). The reconstructed K{sub S}{sup 0} sample is characterized by good event statistics for a wide range in momentum and rapidity. We compare the experimental {pi}{sup -} and K{sub S}{sup 0} distributions to predictions by the Isospin Quantum Molecular Dynamics (IQMD) model. The model calculations show that K{sub S}{sup 0} at low transverse momenta constitute a particularly well-suited tool to investigate the kaon in-medium potential. Our K{sub S}{sup 0} data suggest a strong repulsive in-medium K{sup 0} potential of about 40 MeV strength.
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 pi0-Dalitz to the rho/omega! ...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
E
kin
=
2
GeV
⋅
A
. The analysis methods are briefly outlined and a comparison with detailed Monte-Carlo simulations is shown.
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