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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 σ = 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 Gbitls 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. [ABSTRACT FROM AUTHOR]

In-medium effects on K and ω mesons, which have been reported in the past, confirm the importance of experiments which study hadron properties in excited and normal nuclear matter with penetrating probes. The HADES experiment at GSI uses proton and nuclear beams to record experimental data on elementary and nuclear collisions. This second generation high acceptance detector system allows to detect and separate electron-positron pairs in a high multiplicity environment with a hadron suppression factor of 10−9. Preliminary results on dilepton production in C+C collisions at 2 GeV per nucleon are presented. The comparison with UrQMD calculation shows agreement at the 20% level except at invariant masses below 100 MeV where deviations of up to 50% have been traced to shortcomings in the analysis. [ABSTRACT FROM AUTHOR]

Experiment NA49 at the CERN SPS employs a large acceptance detector to study particle spectra, yields and correlations in nucleus-nucleus, nucleon-nucleus and nucleon-nucleon collisions. Preliminary results on pion, kaon, A and Ā production in central Pb+Pb collisions at 40, 80 and 158 A·GeV beam energy are shown and compared to measurements at lower and higher energies. [ABSTRACT FROM AUTHOR]

Production cross-sections of charged pions, kaons and antikaons have been measured in C+C and C+Au collisions at beam energies of 1.0 and 1.8 AGeV for different polar emission angles. The kaon and antikaon energy spectra can be described by Boltzmann distributions whereas the pion spectra exhibit an additional enhancement at low energies. The pion multiplicity per participating nucleon M(π+)/< Apart> is a factor of about 3 smaller in C+Au than in C+C collisions at 1.0 AGeV whereas it differs only little for the C and the Au target at a beam energy of 1.8 AGeV. The K+ multiplicities per participating nucleon M(K+)/ < Apart> are independent of the target size at 1 AGeV and at 1.8 AGeV. The K- multiplicity per participating nucleon M(K-)/ < Apart> is reduced by a factor of about 2 in C+Au as compared to C+C collisions at 1.8 AGeV. This effect might be caused by the absorption of antikaons in the heavy target nucleus. Transport model calculations underestimate the K-/K+ ratio for C+C collisions at 1.8 AGeV by a factor of about 4 if in-medium modifications of K-mesons are neglected. [ABSTRACT FROM AUTHOR]

Double differential cross sections of positively charged pions and protons have been measured in nuclear collisions of mass-symmetric systems (Ne+NaF, Ni+Ni, Au+Au, Bi+Pb) at incident energies between 0.8 and 1.8 AGeV as a function of the centrality of the reaction. Using a magnetic spectrometer pions and protons were detected with laboratory angles between 40 and 48 degrees, and with momenta up to about 1400 MeV/c. This setting allows for the study of pions and protons emitted close to midrapidity. The center-of-mass pion spectra deviate from a Boltzmann distribution. The inverse slope parameters of the high-energetic pions are smaller than those of the proton spectra and they exhibit a weaker centrality dependence. A scenario is presented where the shape of the pion spectra reflects the decay kinematics of nucleonic resonances embedded in the thermal and the collective motion of the nucleons in the reaction zone. The number of emitted pions per participating nucleon is higher for light than for heavy mass systems. For a given mass system, the total pion multiplicity increases linearly with the number of participating nucleons, whereas the multiplicity of high-energy pions increases more than linearly. This result is consistent with a scenario where the high-energy pions are produced in multiple energetic baryon-baryon collisions occurring in the high-density phase of the collision. [ABSTRACT FROM AUTHOR]

Midrapidity protons fromBi+Bi collisions were measured with the Kaon Spectrometer at SIS at incident energies of E/A=400, 700 and 1000 MeV. Additionally, light fragments were analysed at 400 MeV. We have investigated the azimuthal emission pattern of the particles relative to the reaction plane as function of transverse momentum, bombarding energy and impact parameter. We observe an enhanced emission of particles perpendicular to the reaction plane at all bombarding energies. The ratio of the number of particles emitted out-of-plane/in-plane increases strongly with the particles transverse momentum. The anisotropy decreases with increasing beam energy. Composite particles show a much stronger effect than protons. [ABSTRACT FROM AUTHOR]

Subthreshold kaon production has been studied in symmetric nucleus-nucleus collisions as a function of the nucleus mass, beam energy and centrality. In Au+Au collsions at 1 AGeV the K multiplicity increases more than linearly with increasing number of participating nucleons. Transport calculations have to assume a soft equation of state in order to reproduce the data. The in-medium K cross section measured in Ni+Ni collisions is enhanced by about a factor of 7 as compared to the free cross section when using the K cross section at equivalent beam energies as a normalization. [ABSTRACT FROM AUTHOR]

Approximately 10 Σ decays of the stopping K film (80 cm Saclay HBC) have been measured with the Heidelberg KONRAD-system. This system is capable of detecting about 75% of the Σ→ ne¯ v decays. In addition, about 10 pictures have been scanned for Σ leptonic decays with secondary particle momenta below 80 MeV/c. This covers about 15% of the lepton spectrum. The data yield the following branching ratios: Since only a part of the lepton spectra is detected, the branching ratios depend slightly on the form of the transition matrix elements. The values quoted above were derived taking the Cabibbo solution g/f=−0.24 and the CVC prediction f/f=−1.14. The branching ratios are in good agreement with μ, e universality. [ABSTRACT FROM AUTHOR]

In this contribution we shall discuss some aspects of the role of elementary reference data for the interpretation of the results from nuclear collisions and show in particular that neutron-proton interactions play a significant role. Furthermore we point out that a complete set of elementary data is desirable, because most theoretical concepts for the interpretation of nuclear collisions rely on such data as input for their calculations. [ABSTRACT FROM AUTHOR]