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We report on baryon resonance production and decay in proton-proton collisions at a kinetic energy of 3.5 GeV based on data measured with HADES. The exclusive channels
and
as well as
are studied ...simultaneously for the first time. The invariant masses and angular distributions of the pion-nucleon systems were studied and compared to simulations based on a resonance model ansatz assuming saturation of the pion production by an incoherent sum of baryonic resonances (
R
with masses < 2 GeV/c
2
. A very good description of the one-pion production is achieved allowing for an estimate of individual baryon resonance production cross sections which are used as input to calculate the dielectron yields from
decays. Two models of the resonance decays into dielectrons are examined assuming a point-like
coupling and the dominance of the
meson. The results of model calculations are compared to data from the exclusive
channel by means of the dielectron and
invariant mass distributions.
Fragment distributions have been measured for Au+Au collisions at ital E/ital A=100 and 1000 MeV. A high detection efficiency for fragments was obtained by combining the ALADIN spectrometer and the ...MSU-Miniball/WU-Miniwall array. At both energies the maximum multiplicity of intermediate mass fragments (IMF) normalized to the size of the decaying system is about one IMF per 30 nucleons but the element distributions show significant differences. Within a coalescence picture the suppression of heavy fragments in central collisions at ital E/ital A=100 MeV may be related to a reduction of the density in momentum space which is caused by the collective expansion.
We present the inclusive invariant mass, transverse momentum and rapidity distributions of dielectrons (e+e- pairs) in p+p interactions at 3.5GeV beam kinetic energy. In the vector meson mass region, ...a distinct peak corresponding to direct ω decays is reconstructed with a 2% mass resolution. The data is compared to predictions from three model calculations. Due to the large acceptance of the HADES apparatus for e+e- invariant masses above 0.2 GeV/c 2 and for transverse pair momenta p t < 1 GeV/c, acceptance corrections are, to a large extent, model independent. This allows us to extract from dielectron data for the first time at this energy the inclusive production cross-sections for light vector mesons. Inclusive production cross-sections for π0 and η mesons are also reported. The obtained results will serve as an important reference for the study of vector meson production in proton-nucleus and heavy-ion collisions. Furthermore, using this data, an improved value for the upper bound of the branching ratio for direct η decays into the electron-positron channel is obtained.
Baryon resonance production in proton-proton collisions at a kinetic beam energy of 1.25GeV is investigated. The multi-differential data were measured by the HADES Collaboration. Exclusive channels ...with one pion in the final state (
npπ
+
and
ppπ
0
were put to extended studies based on various observables in the framework of a one-pion exchange model and with solutions obtained within the framework of a partial wave analysis (PWA) of the Bonn-Gatchina group. The results of the PWA confirm the dominant contribution of the
Δ
(1232), yet with a sizable impact of the
N
(1440) and non-resonant partial waves.
We report on the results of experiments performed to investigate the
58Ni+
58Ni 30 MeV/nucleon reaction. In midperipheral collisions a massive fragment (4⩽
Z⩽12) production has been observed. The ...emission patterns exhibit features consistent with dynamical fragmentation of a neck zone between the interacting nuclei, while in addition and at the same time, the projectile-like and target-like residues are subject to statistical decay. The nature of the fragments produced via the two different mechanisms differ both for what concerns charge distribution and isotopic composition. In particular, neutron rich fragments can be produced in dynamical processes, even if the starting nuclear matter presents a
N/
Z ratio close to the unity.
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.
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