In this paper we report on the investigation of baryonic resonance production in proton-proton collisions at kinetic energy 1.25 GeV measured with HADES. Exclusive channels ppe+e- and ppe+e-γ as well ...as ppπ0 and npπ+ were studied. The resonance cross section was determined from hadronic channels in the framework of a one boson exchange model with the accuracy of 15%. The dilepton analysis proved the resonance origin of e+e- pairs and the Δ Dalitz decay was identified experimentally (in the pe+e- channel) for the first time. Investigation of hadronic reaction channels by means of the Partial Wave Analysis revealed a dominant contribution of P33(1232) but also sizeable non-resonant terms and interference effects.
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
−
π
0
) in the final state are presented.
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
−
π
0
) in the final state are presented.
The design of straw tube detector modules developed for the PANDA Forward Tracker is presented. One module consists of 32 straws with 10 mm diameter, arranged in two staggered layers, and has a very ...low material budget of only 8.8ċ10−4X0. The overpressure of the working gas mixture of 1 bar makes the module self-supporting and enables the use of lightweight and compact support frames. Detection planes in the Forward Tracker consist of modules mounted closely, without gaps, next to each other on a support frame. A module can be mounted and dismounted from the frame without the need to remove the neighboring modules, enabling fast repairs. Technical details of the detector design and the assembly procedure of the straw tubes and the straw modules as well as results of performed tests of the modules are given.
The design of the Forward Tracker for the Forward Spectrometer of the PANDA experiment is described. The tracker consists of 6 tracking stations, each comprising 4 planar double layers of straw tube ...detectors, and has a total material budget of only 2% X0. The straws are made self-supporting by a 1 bar over-pressure of the working gas mixture (Ar/CO2). This allows to use lightweight and compact rectangular support frames for the double layers and to split the frames into pairs of C-shaped half-frames for an easier installation on the beam line.
About 10 μs after the Big Bang, the universe was filled—in addition to photons and leptons—with strong-interaction matter consisting of quarks and gluons, which transitioned to hadrons at ...temperatures close to kT = 150 MeV and densities several times higher than those found in nuclei. This quantum chromodynamics (QCD) matter can be created in the laboratory as a transient state by colliding heavy ions at relativistic energies. The different phases in which QCD matter may exist depend for example on temperature, pressure or baryochemical potential, and can be probed by studying the emission of electromagnetic radiation. Electron–positron pairs emerge from the decay of virtual photons, which immediately decouple from the strong interaction, and thus provide information about the properties of QCD matter at various stages. Here, we report the observation of virtual photon emission from baryon-rich QCD matter. The spectral distribution of the electron–positron pairs is nearly exponential, providing evidence for a source of temperature in excess of 70 MeV with constituents whose properties have been modified, thus reflecting peculiarities of strong-interaction QCD matter. Its bulk properties are similar to the dense matter formed in the final state of a neutron star merger, as apparent from recent multimessenger observation.
The global polarization of Λ hyperons along the total orbital angular momentum of a relativistic heavy-ion collision is presented based on the high statistics data samples collected in Au+Au ...collisions at sNN=2.4 GeV and Ag+Ag at 2.55 GeV with the High-Acceptance Di-Electron Spectrometer (HADES) at GSI, Darmstadt. This is the first measurement below the strangeness production threshold in nucleon-nucleon collisions. Results are reported as a function of the collision centrality as well as a function of the hyperon's transverse momentum (pT) and rapidity (yCM) for the range of centrality 0–40%. We observe a strong centrality dependence of the polarization with an increasing signal towards peripheral collisions. For mid-central (20 – 40%) collisions the polarization magnitudes are 〈PΛ〉(%)=6.8±1.3(stat.)±2.1(syst.) for Au+Au and 〈PΛ〉(%)=6.2±0.4(stat.)±0.6(syst.) for Ag+Ag, which are the largest values observed so far. This observation thus provides a continuation of the increasing trend previously observed by STAR and contrasts expectations from recent theoretical calculations predicting a maximum in the region of collision energies about 3 GeV. The observed polarization is of a similar magnitude as predicted by 3D-fluid-dynamics and the UrQMD plus thermal vorticity model and significantly above results from the AMPT model.
We present data on charged kaons (K±) and ϕ mesons in Au(1.23A GeV)+Au collisions. It is the first simultaneous measurement of K− and ϕ mesons in central heavy-ion collisions below a kinetic beam ...energy of 10A GeV. The ϕ/K− multiplicity ratio is found to be surprisingly high with a value of 0.52±0.16 and shows no dependence on the centrality of the collision. Consequently, the different slopes of the K+ and K− transverse-mass spectra can be explained solely by feed-down, which substantially softens the spectra of K− mesons. Hence, in contrast to the commonly adapted argumentation in literature, the different slopes do not necessarily imply diverging freeze-out temperatures of K+ and K− mesons caused by different couplings to baryons.
•A semi-analytical method is proposed to the 3D pattern recognition of particle traces.•Particles move on straight line in absence of magnetic field and on helix inside.•The efficiency for events ...with 5 tracks is above 91% for higher energy, 79% for 0.55 GeV/c.
In this study, we present an algorithm for 3D track finding in the Forward Tracker of the PANDA experiment. This tracker is based on straw tube detectors and is designed to measure the deflection of particles in the magnetic field of the PANDA dipole magnet in order to determine their momenta. The algorithm uses the track road method for selecting track candidates. The applied track model in the projection onto the bending plane in the region before, inside and after the dipole magnet gap consists of line, circle and line, respectively. In the non-bending plane, a track projection is represented by a straight line. The algorithm was tested using simulated tracks of muons and obtained results for the track finding efficiency and for the momentum resolution are presented.
.
The centrality determination for Au + Au collisions at 1.23
A
GeV, as measured with HADES at the GSI-SIS18, is described. In order to extract collision geometry related quantities, such as the ...average impact parameter or number of participating nucleons, a Glauber Monte Carlo approach is employed. For the application of this model to collisions at this relatively low centre-of-mass energy of
s
NN
=
2
.
42
GeV special investigations were performed. As a result a well defined procedure to determine centrality classes for ongoing analyses of heavy-ion data is established.
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