Differential production cross sections of K
− and K
+ mesons have been measured as function of the polar emission angle in Ni
+
Ni collisions at a beam energy of 1.93
A
GeV. In near-central ...collisions, the spectral shapes and the widths of the rapidity distributions of K
− and K
+ mesons are in agreement with the assumption of isotropic emission. In non-central collisions, the K
− and K
+ rapidity distributions are broader than expected for a single thermal source. In this case, the polar angle distributions are strongly forward–backward peaked and the nonisotropic contribution to the total yield is about one third both for K
+ and K
− mesons. The K
−/K
+ ratio is found to be about 0.03 independent of the centrality of the reaction. This value is significantly larger than predicted by microscopic transport calculations if in-medium modifications of K mesons are neglected.
.
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.
HADES is a running spectrometer installed at GSI, Germany. PANDA and CBM are planned detector systems for the new FAIR facility at GSI. For these detectors, a general-purpose trigger and readout ...board with on-board DAQ functionality was developed. The original motivation for this project was the implementation of a 128-channel time to digital converter (TDC) with a time resolution of sigma=40 ps based on the HPTDC chip from CERN into a fully fledged data acquisition system. The application of the board is detector independent, includes a 2 Gbit/s optical link and has the option to employ the TDC chips and/or to integrate versatile add-on boards through 16 Gbit/s connectors. The latter one may interface to the front end electronics of other types of detectors. A large FPGA (Xilinx Virtex 4 LX40) and a TigerSharc DSP can be used as on-board resources for trigger and on-line analysis algorithms. Data transfer to mass storage and slow control is done via an ETRAX processor running Linux and a 100 Mbit/s Ethernet interface.
Results on the production of the double strange cascade hyperon Ξ^{-} 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. For the first time, subthreshold Ξ^{-} production is observed in proton-nucleus interactions. Assuming a Ξ^{-} phase-space distribution similar to that of Λ hyperons, the production probability amounts to P_{Ξ^{-}}=2.0±0.4(stat)±0.3(norm)±0.6(syst)×10^{-4} resulting in a Ξ^{-}/(Λ+Σ^{0}) ratio of P_{Ξ^{-}}/P_{Λ+Σ^{0}}=1.2±0.3(stat)±0.4(syst)×10^{-2}. Available model predictions are significantly lower than the measured Ξ^{-} yield.
Results of resonance searches in the Xi(-)pi(-), Xi(-)pi(+), Xi;(+)pi(-), and Xi;(+)pi(+) invariant mass spectra in proton-proton collisions at sqrts=17.2 GeV are presented. Evidence is shown for the ...existence of a narrow Xi(-)pi(-) baryon resonance with mass of 1.862+/-0.002 GeV/c(2) and width below the detector resolution of about 0.018 GeV/c(2). The significance is estimated to be above 4.2sigma. This state is a candidate for the hypothetical exotic Xi(--)(3/2) baryon with S=-2, I=3 / 2, and a quark content of (dsdsū). At the same mass, a peak is observed in the Xi(-)pi(+) spectrum which is a candidate for the Xi(0)(3/2) member of this isospin quartet with a quark content of (dsus-d). The corresponding antibaryon spectra also show enhancements at the same invariant mass.
The production of charged pions in minimum bias p+C interactions is studied using a sample of 377000 inelastic events obtained with the NA49 detector at the CERN SPS at 158 GeV/c beam momentum. The ...data cover a phase space area ranging from 0 to 1.8 GeV/c in transverse momentum and from -0.1 to 0.5 in Feynman xF. Inclusive invariant cross sections are given on a grid of 270 bins per charge, thus offering for the first time a dense coverage of the projectile hemisphere and of the cross-over region into the target fragmentation zone.
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