Results on $\Lambda$ hyperon production are reported for collisions of p(3.5 GeV) + Nb, studied with the High Acceptance Di-Electron Spectrometer (HADES) at SIS18 at GSI Helmholtzzentrum for ...Heavy-Ion Research, Darmstadt. The transverse mass distributions in rapidity bins are well described by Boltzmann shapes with a maximum inverse slope parameter of about $90\,$MeV at a rapidity of $y=1.0$, i.e. slightly below the center-of-mass rapidity for nucleon-nucleon collisions, $y_{cm}=1.12$. The rapidity density decreases monotonically with increasing rapidity within a rapidity window ranging from 0.3 to 1.3. The $\Lambda$ phase-space distribution is compared with results of other experiments and with predictions of two transport approaches which are available publicly. None of the present versions of the employed models is able to fully reproduce the experimental distributions, i.e. in absolute yield and in shape. Presumably, this finding results from an insufficient modelling in the transport models of the elementary processes being relevant for $\Lambda$ production, rescattering and absorption. The present high-statistics data allow for a genuine two-dimensional investigation as a function of phase space of the self-analyzing $\Lambda$ polarization in the weak decay $\Lambda\rightarrow p \pi^-$. Finite negative values of the polarization in the order of $5-20\,%$ are observed over the entire phase space studied. The absolute value of the polarization increases almost linearly with increasing transverse momentum for $p_t>300\,$MeV/c and increases with decreasing rapidity for $y < 0.8$.
Development of FARICH-detector for ALICE experiment at CERN Berlev, A.I.; Danilyuk, A.F.; Karavicheva, T.L. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
2009, 2009-1-00, Letnik:
598, Številka:
1
Journal Article
Recenzirano
In order to extend the momentum range of the charged particle identification up to 10
GeV
/c for pion–kaon separation and to 14
GeV
/c for kaon–proton separation of the ALICE experiment at LHC ...(CERN), the focusing aerogel ring imaging Cherenkov (FARICH) detector employing a multi-layer silica aerogel as radiator has been proposed. The design project of the FARICH Prototype is presented.
Results of the test of the avalanche photo-diodes with metal-resistance-semiconductor structure produced by the Centre of Perspective Technology and Apparatus (CPTA MRS APDs) are shown. Preliminary data of tests of the light-collecting capability for aluminum and stainless steel Winston cone holes of different types are presented.
The performance of the proposed detector was estimated using the GEANT4 simulation. Results of the optimization of characteristics of the aerogel radiators, CPTA MRS APDs with and without wavelength shifter paint are discussed.
Hadron modifications in nuclear matter are discussed in connection to chiral symmetry restoration and/or hadronic many body effects. Experiments with photon, proton and heavy ion beams are used to ...probe properties of hadrons embedded in nuclear matter at different temperatures and densities. Most of the information has been gathered for the light vector mesons ρ ω and ø. HADES is a second generation experiment operating at GSI with the main aim to study in-medium modifications by means of dielectron production at the SIS18/Bevelac energy range. Large acceptance and excellent particle identification capabilities allows also for measurements of strangeness production. These abilities combined with the variety of beams provided by the SIS18 allow for a characterization of properties of the dense baryonic matter properties created in heavy ion collisions at these energies. A review of recent experimental results obtained by HADES is presented, with main emphasis on hadron properties in nuclear matter.
Wire GEM detector Ovchinnikov, B. M.; Razin, V. I.; Reshetin, A. I. ...
Instruments and experimental techniques (New York),
03/2010, Letnik:
53, Številka:
2
Journal Article
Recenzirano
A wire GEM (WGEM) detector with a gas gap between meshes was constructed. The detector provides the amplification 5 × 10
4
for the gas mixture of Ar + 20% CO
2
at atmospheric pressure. As compared ...with well-known GEM detectors produced by perforation the plastic plate metallized on both sides the WGEM does not suffer from breakdowns between its electrodes and the effect of accumulation of charges on holes’ walls is absent. As a result the WGEM has high reliability and stability.
A high-statistic data sample of Ar(1.76 AGeV)+KCl events recorded with HADES is used to search for a hypertriton signal. An upper production limit per centrality-triggered event of
on the 3
level is ...derived. Comparing this value with the number of successfully reconstructed
hyperons allows to determine an upper limit on the ratio
, which is confronted with statistical and coalescence-type model calculations.
Recent results on spin effects in few nucleon systems obtained at Nuclotron-JINR are presented. The data on the deuteron analyzing powers in different reactions in the wide energy range demonstrate ...the sensitivity to the short-range spin structure of the light nuclei. The future plans on the studies with polarized deuterons from new polarized ion source at Nuclotron will be reported.
.
Results on the deep sub-threshold production of the short-lived hadronic resonance K*(892)
0
are reported for collisions of Ar + KCl at 1.76A GeV beam energy, studied with the High Acceptance ...Di-Electron Spectrometer (HADES) at SIS18/GSI. The K*(892)
0
production probability per central collision of
and the K*(892)
0
/K
0
ratio of
are determined at the lowest energy so far (
i.e.
deep below the threshold for the corresponding production in nucleon-nucleon collisions,
MeV). The K*
0
/K
0
ratio is compared with results of other experiments and with the predictions of the UrQMD transport approach and of the statistical hadronization model. The experimental K*
0
yield and the K*
0
/K
0
ratio are overestimated by the transport model by factors of about five and two, respectively. In a chemically equilibrated medium the ratio corresponds to a temperature of the thermalized system being systematically lower than the value determined by the yields of the stable and long-lived hadrons produced in Ar + KCl collisions. From the present measurement, we conclude that sub-threshold K* production either cannot be considered to proceed in a system being in thermal equilibrium or these short-lived resonances appear undersaturated, for example as a result of the rescattering of the decay particles in the ambient hadronic medium.
The cross sections of forward emission of one, two and three neutrons by 158A GeV 115In nuclei in collisions with Al, Cu, Sn and Pb targets are reported. The measurements were performed in the ...framework of the ALICE-LUMI experiment at the SPS facility at CERN. Various corrections accounting for the absorption of beam nuclei and produced neutrons in target material and surrounding air were introduced. The corrected cross section data are compared with the predictions of the RELDIS model for electromagnetic fragmentation of 115In in ultraperipheral collisions, as well as with the results of the abrasion-ablation model for neutron emission in hadronic interactions. The measured neutron emission cross sections well agree with the RELDIS results, with the exception of In-Al collisions where the measured cross sections are larger compared to RELDIS. This is attributed to a relatively large contribution of hadronic fragmentation of In on Al target with respect to electromagnetic fragmentation, on the contrary to similar measurements performed earlier with 30A GeV 208Pb colliding with Al.
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