J. Mousa

We present phase space distributions and multiplicities of K + , K -, and φ mesons produced in Ar + KCl reactions at a kinetic beam energy of 1.756 GeV/nucleon and measured with the HADES spectrometer.The inverse slope parameters and yields of kaons supplement the systematics of previous measurements.The percentage of K -mesons coming from φ decay is found to be 18 ± 7%.

We present transverse momentum spectra, rapidity distribution and multiplicity of $ \Lambda$ -hyperons measured with the HADES spectrometer in the reaction Ar(1.76AGeV) + KCl . The yield of $ \Xi^{{-}}_{}$ is calculated from our previously reported $ \Xi^{{-}}_{}$ /( $ \Lambda$ + $ \Sigma^{{0}}_{}$ ) ratio and compared to other strange particle multiplicities. Employing a strangeness balance equation the multiplicities of the yet unmeasured $ \Sigma^{{\pm}}_{}$ -hyperons can be estimated. Finally a statistical hadronization model is used to fit the yields of $ \pi^{-}_{}$ , K+, K 0 s , K-, $ \phi$ , $ \Lambda$ and $ \Xi^{-}_{}$ . The resulting chemical freeze-out temperature of T = (76±2) MeV is compared to the measured slope parameters obtained from fits to the transverse mass distributions of the different particles.

The invariant-mass spectrum of $e^+ e^-$ pairs produced in $^{12}$C+$^{12}$C collisions at an incident energy of 2 GeV per nucleon has been measured for the first time. The measured pair production probabilities span over five orders of magnitude from the $\pi^0$-Dalitz to the $\rho/\omega$ invariant-mass region. Dalitz decays of $\pi^0$ and $\eta$ account for all the yield up to 0.15 GeV/c$^2$, but for only about 50% above this mass. A comparison with model calculations shows that the excess pair yield is likely due to baryon-resonance and vector-meson decays. Transport calculations based on vacuum spectral functions fail, however, to describe the entire mass region.

We present the transverse momentum spectra and rapidity distributions of ${\ensuremath{\pi}}^{\ensuremath{-}}$ and ${\mathrm{K}}_{S}^{0}$ in Ar $+$ KCl reactions at a beam kinetic energy of $1.756$ $A$ GeV measured with the High Acceptance Di-Electron Spectrometer (HADES). The reconstructed ${\mathrm{K}}_{S}^{0}$ sample is characterized by good event statistics for a wide range in momentum and rapidity. We compare the experimental ${\ensuremath{\pi}}^{\ensuremath{-}}$ and ${\mathrm{K}}_{S}^{0}$ distributions to predictions by the Isospin Quantum Molecular Dynamics (IQMD) model. The model calculations show that ${\mathrm{K}}_{S}^{0}$ at low transverse momenta constitute a particularly well-suited tool to investigate the kaon in-medium potential. Our ${\mathrm{K}}_{S}^{0}$ data suggest a strong repulsive in-medium ${\mathrm{K}}^{0}$ potential of about 40 MeV strength.

The emission of e+e− pairs from C+C collisions at an incident energy of 1 GeV per nucleon has been investigated. The measured production probabilities, spanning from the π0-Dalitz to the ρ/ω invariant-mass region, display a strong excess above the cocktail of standard hadronic sources. The bombarding-energy dependence of this excess is found to scale like pion production, rather than like eta production. The data are in good agreement with results obtained in the former DLS experiment.

We report measurements of electron pair production in elementary p+p and d+p reactions at 1.25 GeV/u with the HADES spectrometer. For the first time, the electron pairs were reconstructed for n+p reactions by detecting the proton spectator from the deuteron breakup. We find that the yield of electron pairs with invariant mass Me+e−>0.15 GeV/c2 is about an order of magnitude larger in n+p reactions as compared to p+p. A comparison to model calculations demonstrates that the production mechanism is not sufficiently described yet. The electron pair spectra measured in C+C reactions are compatible with a superposition of elementary n+p and p+p collisions, leaving little room for additional electron pair sources in such light collision systems.

We present results on dielectron production in 40 Ar+KCl collisions at 1.76A GeV.For the first time ω mesons could be reconstructed in a heavy-ion reaction at a bombarding energy which is well below the production threshold in free nucleon-nucleon collisions.The ω multiplicity has been extracted and compared to the yields of other particles, in particular of the φ meson.At intermediate e + e -invariant masses, we find a strong enhancement of the pair yield over a reference spectrum from elementary nucleon-nucleon reactions suggesting the onset of non-trivial effects of the nuclear medium.Transverse-mass spectra and angular distributions have been reconstructed in three invariant mass bins.In the former unexpectedly large slopes are found for high-mass pairs.The latter, in particular the helicity-angle distributions, are largely consistent with expectations for a pair cocktail dominated at intermediate masses by ∆ Dalitz decays.

We present the inclusive invariant-mass, transverse momentum and rapidity distributions of dielectrons (e$^{+}$e$^{-}$ pairs) in p+p interactions at 3.5 GeV beam kinetic energy. In the vector-meson mass region, a distinct peak corresponding to direct $\omega$ decays is reconstructed with 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 $\pi^o$ and $\eta$ 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 $\eta$ decays into the electron-positron channel is obtained.

The HADES data from p + Nb collisions at a center-of-mass energy of $ \sqrt{s_{NN}} = 3.2$ GeV are analyzed employing a statistical hadronization model. The model can successfully describe the production yields of the identified hadrons $ \pi^{0}$ , $ \eta$ , $ \Lambda$ , K 0 s, $ \omega$ with parameters $ T_{chem} = (99\pm 11)$ MeV and $ \mu_{b} = (619\pm 34)$ MeV, which fit well into the chemical freeze-out systematics found in heavy-ion collisions. In addition, we reanalyze our previous HADES data from Ar + KCl collisions at $ \sqrt{s_{NN}} = 2.6$ GeV with an updated version of the model. We address equilibration in heavy-ion collisions by testing two aspects: the description of yields and the regularity of freeze-out parameters from a statistical model fit as a function of colliding energy and system size. Despite its success, the model fails to describe the observed $ \Xi^{-}$ yields in both, p + Nb and Ar + KCl . Special emphasis is put on feed-down contributions from higher-lying resonance states as a possible explanation for the observed excess.

We present results of an exclusive measurement of the first-excited state of the $\ensuremath{\Sigma}$ hyperon, $\ensuremath{\Sigma}{(1385)}^{+}$, produced in $p+p\ensuremath{\rightarrow}{\ensuremath{\Sigma}}^{+}+{K}^{+}+n$ at $3.5\phantom{\rule{0.28em}{0ex}}\mathrm{GeV}$ beam energy. The extracted data allow the detailed study of the invariant mass distribution of the $\ensuremath{\Sigma}{(1385)}^{+}$. The mass distribution is well described by a relativistic Breit-Wigner function with a maximum at ${m}_{0}=1383.2\ifmmode\pm\else\textpm\fi{}0.9\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}/{c}^{2}$ and a width of $40.2\ifmmode\pm\else\textpm\fi{}2.1\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}/{c}^{2}$. The exclusive production cross section comes out to be $22.27\ifmmode\pm\else\textpm\fi{}0.89\ifmmode\pm\else\textpm\fi{}1.{56}_{\ensuremath{-}2.10}^{+3.07}\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}b$. Angular distributions of the $\ensuremath{\Sigma}{(1385)}^{+}$ in different reference frames are found to be compatible with the hypothesis that $33%$ of $\ensuremath{\Sigma}{(1385)}^{+}$ result from the decay of an intermediate broad ${\ensuremath{\Delta}}^{++}$ excitation at about $2000\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}/{c}^{2}$.

The tagged quasi-free 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 (s∼2.42 GeV/c for the quasi-free collision). For the first time, differential distributions of solid statistics for 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− 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− 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 GeV and with width Γ∼70 MeV.

We present measurements of exclusive \pi^{+,0} and \eta\ production in pp reactions at 1.25 GeV and 2.2 GeV beam kinetic energy in hadron and dielectron channels. In the case of \pi^+ and \pi^0, high-statistics invariant-mass and angular distributions are obtained within the HADES acceptance as well as acceptance corrected distributions, which are compared to a resonance model. The sensitivity of the data to the yield and production angular distribution of \Delta(1232) and higher lying baryon resonances is shown, and an improved parameterization is proposed. The extracted cross sections are of special interest in the case of pp \to pp \eta, since controversial data exist at 2.0 GeV; we find \sigma =0.142 \pm 0.022 mb. Using the dielectron channels, the \pi^0 and \eta\ Dalitz decay signals are reconstructed with yields fully consistent with the hadronic channels. The electron invariant masses and acceptance corrected helicity angle distributions are found in good agreement with model predictions.

Data on inclusive dielectron production are presented for the reaction p+p at 2.2 GeV measured with the High Acceptance DiElectron Spectrometer (HADES). Our results supplement data obtained earlier in this bombarding energy regime by DLS and HADES. The comparison with the 2.09 GeV DLS data is discussed. The reconstructed e+e- distributions are confronted with simulated pair cocktails, revealing an excess yield at invariant masses around 0.5 GeV/c2. Inclusive cross sections of neutral pion and eta production are obtained.

We present the results of a study of charged-pion production in 12C + 12C collisions at incident beam energies of 1A GeV and 2A GeV using the HADES spectrometer at GSI. The main emphasis of the HADES program is on the dielectron signal from the early phase of the collision. Here, however, we discuss the data with respect to the emission of charged hadrons, specifically the production of $ \pi^{{\pm}}_{}$ mesons, which are related to neutral pions representing a dominant contribution to the dielectron yield. We have performed the first large-angular-range measurement of the distribution of $ \pi^{{\pm}}_{}$ mesons for the 12C + 12C collision system covering a fairly large rapidity interval. The pion yields, transverse-mass and angular distributions are compared with calculations done within a transport model, as well as with existing data from other experiments. The anisotropy of pion production is systematically analyzed.

The High Acceptance DiElectron Spectrometer (HADES) has been recently commissioned at GSI Darmstadt. It has been designed to study hadron properties inside nuclear matter via measurements of dielectron decays in proton, pion and heavy ion induced reactions in 1−2 AGeV energy range. We report first preliminary results on invariant masses of e+e− pairs measured in 12C + 12C collisions at E=2 AGeV and compare them to simulations based on UrQMD transport model. In summary we present and discuss planned experiments.

We study the production of Σ±π∓pK+ particle quartets in p + p reactions at 3.5 GeV kinetic beam energy. The data were taken with the HADES experiment at GSI. This report evaluates the contribution of resonances like Λ(1405), Σ(1385)0, Λ(1520), Δ(1232), N⁎ and K⁎0 to the Σ±π∓pK+ final state. The resulting simulation model is compared to the experimental data in several angular distributions and it shows itself as suitable to evaluate the acceptance corrections properly.

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 $ P_{K^{*0}}=(4.4\pm 1.1 \pm 0.5)\times 10^{-4}$ and the K*(892)0/K0 ratio of $ P_{K^{*0}}/P_{K^0}=(1.9\pm 0.5\pm 0.3)\times 10^{-2}$ are determined at the lowest energy so far (i.e. deep below the threshold for the corresponding production in nucleon-nucleon collisions, $ \sqrt{s_{NN}}-\sqrt{s_{thr}}=-340$ MeV). The K*0/K0 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/K0 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.

Results on $\Lambda$p femtoscopy are reported at the lowest energy so far. At a beam energy of 1.76A~GeV, the reaction Ar+KCl was studied with the High Acceptance Di-Electron Spectrometer (HADES) at SIS18/GSI. A high-statistics and high-purity $\Lambda$ sample was collected, allowing for the investigation of $\Lambda$ p correlations at small relative momenta. The experimental correlation function is compared to corresponding model calculations allowing the determination of the space-time extent of the $\Lambda$p emission source. The $\Lambda$p source radius is found slightly smaller than the pp correlation radius for a similar collis ion system. The present $\Lambda$p radius is significantly smaller than that found for Au+Au/Pb+Pb collisio ns in the AGS, SPS and RHIC energy domains, but larger than that observed for electroproduction from He. Taking into account all available data, we find the $\Lambda$p source radius to increase almost linearly with the number of participants to the power of one-third.

Results on pp, π+π+, and π−π− intensity interferometry 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 experimental correlation functions as a function of the relative momentum are compared to model calculations allowing the determination of the space-time extent of the corresponding emission sources. The ππ source radii are found significantly larger than the pp emission radius. The present radii do well complement the beam-energy dependences of Gaussian source radii of the collision system of size A + A ≃ 40 + 40 . The pp source radius at fixed beam energy is found to increase linearly with the cube root of the number of participants. From this trend, a lower limit of the pp correlation radius is deduced.

HADES is a second generation experiment designed to study dielectron production in proton, pion, and heavy ion induced reactions at the GSI accelerator facility in Darmstadt. The physics programme of HADES is focused on in-medium properties of the light vector mesons. In this contribution we present status of the HADES experiment, demonstrate its capability to identify rare dielectron signal, show first experimental results obtained from C+C reactions at 2 A GeV and shortly discuss physics programme of up-coming experimental runs.

The aim of the present analysis is to determine the relative production cross sections of the $\Lambda$(1405) and $\Sigma(1385)^{0}$ resonances in p+p collisions at E$_{kin}$=3.5 GeV measured with HADES. Upper and lower limits have been determined for the ratio $\sigma_{(\Sigma(1385)^{0}+p+K^{+})}/\sigma_{(\Lambda(1405)+p+K^{+})}=0.76_{-0.26}^{+0.54}$. The knowledge of this ratio is an essential input for the analysis of the decay $\Lambda(1405)\rightarrow\Sigma^{\pm}\pi^{\mp}$, where an unambiguous separation of the $\Lambda$(1405) and $\Sigma(1385)^{0}$ signals is not possible.

This paper is a summary of a research and development programme, conducted during the past 3 years on the CMS Preshower silicon sensors to define the specifications. The main purpose was to study the radiation hardness of these devices resulting from the specific design (metal lines wider than the p+ implants) and the production technology, a deep n+ layer on the ohmic side. An acceptable noise and a uniform charge collection were guaranteed by an appropriate choice of the interstrip region width. About 65 sensors, of different designs and produced by six manufacturers, were irradiated with neutrons and protons and thoroughly tested before and after irradiation. The results of the tests and the final specifications are presented.

e + e - production was studied using the High Acceptance DiElectron Spectrometer (HADES). In pp collisions at 2.2GeV kinetic beam energy, the exclusive η production and the Dalitz decay η→γe + e - have been reconstructed. The electromagnetic form factor of the latter decay was found to be in good agreement with the existing theoretical predictions. In addition, an inclusive e + e - invariant-mass spectrum from the 12C + 12C reaction at 2AGeV is presented and compared with a simplified thermal model.

The HADES experiment, installed at GSI, Darmstadt, measures di-electron production in A + A, p/π + N and p/π + A collisions. Here, the π 0 and η Dalitz decays have been reconstruced in the exclusive p + p reaction at 2.2 GeV to form a reference cocktail for long-lived di-electron sources. In the C + C reaction at 1 and 2 GeV/u, these long-lived sources have been subtracted from the measured inclusive e + e - yield to exhibit the signal from the early phase of the collision. The results suggest that resonances play an important role in dense nuclear matter.

Results of a study of charged pion production in 12C+12C collisions at incident beam energies of 1A GeV and 2A GeV, and 40Ar+natKCl at 1.76AGeV, using the spectrometer HADES at GSI, are presented. We have performed a measurement of the transverse momentum distributions of pi+- mesons covering a fairly large rapidity interval, in case of the C+C collision system for the first time. The yields, transverse mass and angular distributions are compared with a transport model as well as with existing data from other experiments.

The High Acceptance DiElectron Spectrometer HADES has been recently commissioned at GSI, Darmstadt. It has been designed for systematic studies of hadron properties inside nuclear matter. We report first preliminary results on invariant masses e+e--pairs which were measured in 12C + 12C collisions at Ekin=2 GeV⋅A. The analysis methods are briefly outlined and a comparison with detailed Monte-Carlo simulations is shown.

This research aims to introduce Goal-Oriented Requirements Engineering (GORE), defining what is meant by a goal, the main differences between goal and requirement, also the types of goals and the sources of extracting these goals, in addition, the birth of goal modelling techniques and the reason behind using goal modelling, at last, the goal-oriented approaches, early and late requirements goal modelling techniques, this research tries to get out with the result of how goal modelling is very important in requirements engineering, in order to extract the goals and requirements in correspondence to business context, which in turn will aid in better analyses and extract the functions and processes in any organization or business.

A system for capturing and processing data, from radiation detectors, in the field of X-ray crystallography has been developed. The system includes a custom-made mixed analog-digital 16-channel VLSI circuit in 50 μm pitch. Each channel comprises a charge amplifier, a shaper, a comparator and a 21-bit counter. The circuit can be scaled in a daisy chain configuration. Data acquisition is performed with a custom made PCI card while the control software is developed with Visual C++ under the MS Windows NT environment. Performance of a fully operational system, in terms of electronic noise, statistical variations and data capture speed is presented. The noise level permits counting of X-rays down to 8 keV while the counting capability is in excess of 200 kHz. The system is intended for X-ray crystallography with silicon detectors.

HADES is a secondary generation experiment operated at GSI Darmstadt with the main goal to study dielectron production in proton, pion and heavy ion induced reactions. The first part of the HADES mission is to reinvestigate the puzzling pair excess measured by the DLS collaboration in C + C and Ca + Ca collisions at 1 A GeV. For this purpose dedicated measurements with the C + C system at 1 and 2 A GeV were performed. The pair excess above a cocktail of free hadronic decays has been extracted and compared to the one measured by DLS. Furthermore, the excess is confronted with predictions of various model calculations.

Currently, the HADES spectrometer undergoes un upgrade program to be prepared for measurements at the upcoming SIS-100 synchrotron at FAIR. We describe the current status of the HADES di-electron measurements at the SIS-18 and our future plans for SIS-100.

Systematic investigations of dilepton production are performed at the SIS accelerator of GSI with the HADES spectrometer. The goal of this program is a detailed understanding of di-electron emission from hadronic systems at moderate temperatures and densities. New results obtained in HADES experiments focussing on electron pair production in elementary collisions are reported here. They pave the way to a better understanding of the origin of the so-called excess pairs earlier on observed in heavy-ion collisions by the DLS collaboration and lately confirmed in two measurements of the HADES collaboration using C+C and Ar+KCl collisions. Results of these studies are discussed.

The present paper reports on a complete diffraction pattern obtained with a 32 channel Si microstrip detector when a standard ZnO sample is illuminated with 8.04 keV photons. Information from single photon conversion in each detector channel is routed to a VLSI readout chain that contains analog amplification, pulse shaping, digitization and counting circuitry for each individual channel. The read out pitch is 200 /spl mu/m and data acquisition is performed with a custom made PC card. The current system represents an intermediate step toward a long linear array for powder X-ray crystallography.

The High Acceptance Di-Electron Spectrometer HADES 1 has been constructed at the SIS accelerator (GSI Darmstadt) to investigate electron-positron pairs produced in proton, pion and heavy ion induced reactions. The main goal of these studies is to explore properties of hadrons in nuclear matter. The apparatus and the experimental results from C + C at 2.0 AGeV and 1.0 AGeV and p + p at 2.2 GeV compared with Monte-Carlo events from a generator based on known cross-sections and branching ratios are presented.

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 $ 1.04\times 10^{-3}$ on the 3 $ \sigma$ level is derived. Comparing this value with the number of successfully reconstructed $ \Lambda$ hyperons allows to determine an upper limit on the ratio $ N_{_{\Lambda}^{3}H}/N_{\Lambda}$ , which is confronted with statistical and coalescence-type model calculations.

One of the main goals of the HADES experiment is to achieve a detailed understanding of dielectron emission from hadronic systems at moderate bombarding energies. Results obtained on electron pair production in elementary N+N collisions pave the way to a better understanding of the origin of the pair excess seen in heavy-ion collisions. This puzzling excess, reported first by the former DLS experiment, is now being investigated systematically by HADES.

We present the transverse momentum spectra and rapidity distributions of $\pi^{-}$ and K$^0_S$ in Ar+KCl reactions at a beam kinetic energy of 1.756 A GeV measured with the spectrometer HADES. The reconstructed K$^0_S$ sample is characterized by good event statistics for a wide range in momentum and rapidity. We compare the experimental $\pi^{-}$ and K$^0_S$ distributions to predictions by the IQMD model. The model calculations show that K$^0_S$ at low tranverse momenta constitute a particularly well suited tool to investigate the kaon in-medium potential. Our K$^0_S$ data suggest a strong repulsive in-medium K$^0$ potential of about 40 MeV strength.

The HADES Collaboration G. Agakishiev, C. Agodi, A. Balanda, G. Bellia, D. Belver, A. Belyaev, J. Bielcik, A. Blanco, A. Bortolotti, J.L. Boyard, P. Braun-Munzinger, P. Cabanelas, S. Chernenko, T. Christ, R. Coniglione, M. Destefanis, J. Diaz, F. Dohrmann, I. Duran, A. Dybczak, T. Eberl, L. Fabbietti, O. Fateev, R. Ferreira-Marques, P. Finocchiaro, P. Fonte, J. Friese, I. Frohlich, T. Galatyuk, J.A. Garzon, R. Gernhauser, A. Gil, C. Gilardi, M. Golubeva, D. Gonzalez-Diaz, E. Grosse, F. Guber, M. Heilmann, T. Heinz, T. Hennino, R. Holzmann, A. Ierusalimov, I. Iori, A. Ivashkin, M. Jurkovic, B. Kampfer, K. Kanaki, T. Karavicheva, D. Kirschner, I. Koenig, W. Koenig, B.W. Kolb, R. Kotte, A. Kozuch, A. Krasa, F. Křižek, R. Krucken, W. Kuhn, A. Kugler, A. Kurepin, J. Lamas-Valverde, S. Lang, J.S. Lange, K. Lapidus, L. Lopes, M. Lorenz, L. Maier, C. Maiolino, A. Mangiarotti, J. Maŕin, J. Markert, V. Metag, B. Michalska, J. Michel, E. Moriniere, J. Mousa , M. Munch, C. Muntz, L. Naumann, R. Novotny, J. Otwinowski, Y.C. Pachmayer, M. Palka, Y. Parpottas, V. Pechenov, O. Pechenova, T. Perez Cavalcanti, P. Piattelli, J. Pietraszko, V. Posṕisil, W. Przygoda, B. Ramstein, A. Reshetin, M. Roy-Stephan, A. Rustamov, A. Sadovsky, B. Sailer, P. Salabura, P. Sapienza, A. Schmah, C. Schroeder, E. Schwab, R.S. Simon, Yu.G. Sobolev, S. Spataro, B. Spruck, H. Strobele, J. Stroth, C. Sturm, M. Sudol, A. Tarantola, K. Teilab, P. Tlustý, M. Traxler, R. Trebacz, H. Tsertos, V. Wagner, M. Weber, M. Wisniowski, T. Wojcik, J. Wustenfeld, S. Yurevich, Y. Zanevsky, P. Zhou, and P. Zumbruch 1 Istituto Nazionale di Fisica Nucleare Laboratori Nazionali del Sud, 95125 Catania, Italy 2 LIP-Laboratorio de Instrumentacao e Fisica Experimental de Particulas, 3004-516 Coimbra, Portugal 3 Smoluchowski Institute of Physics, Jagiellonian University of Cracow, 30-059 Krakow, Poland 4 GSI Helmholtzzentrum fur Schwerionenforschung, 64291 Darmstadt, Germany 5 Institut fur Strahlenphysik, Forschungszentrum Dresden-Rossendorf, 01314 Dresden, Germany 6 Joint Institute of Nuclear Research, 141980 Dubna, Russia 7 Institut fur Kernphysik, Johann Wolfgang Goethe-Universitat, 60438 Frankfurt, Germany 8 II. Physikalisches Institut, Justus Liebig Universitat Giessen, 35392 Giessen, Germany 9 Istituto Nazionale di Fisica Nucleare, Sezione di Milano, 20133 Milano, Italy 10 Institute for Nuclear Research, Russian Academy of Science, 117312 Moscow, Russia 11 Physik Department E12, Technische Universitat Munchen, 85748 Munchen, Germany 12 Department of Physics, University of Cyprus, 1678 Nicosia, Cyprus 13 Institut de Physique Nucleaire (UMR 8608), CNRS/IN2P3 Universite Paris Sud, F-91406 Orsay Cedex, France 14 Nuclear Physics Institute, Academy of Sciences of Czech Republic, 25068 Rez, Czech Republic 15 Departamento de Fisica de Particulas, University of Santiago de Compostela, 15782 Santiago de Compostela, Spain 16 Instituto de Fisica Corpuscular, Universidad de Valencia-CSIC, 46971 Valencia, Spain

We report on a measurement of electron pair production in 12 C+ 12 C collisions at an incident energy of 2 GeV per nucleon with the HADES spectrometer.The measured pair production probabilities span over five orders of magnitude from the π 0 -Dalitz to the ρ/ω invariant-mass region.Dalitz decays of π 0 and η account for all the yield up to 0.15 GeV/c 2 , but for only about 50% above this mass.The excess yield is in agreement with the former DLS result if one assumes that it scales with beam energy like pion production.A preliminary analysis of 12 C+ 12 C collisions at an incident energy of 1 A GeV, measured with the HADES detector, supports this scenario.

A.KUGLER’, H.AGAKICHIEV’, C.AG~DI~, MALVAREZ-PARDON, HALVAREZ-PoL’, E.BADIJRA’, A.BALANDA’, F.BALLESTER~, A.BAssI*, R.BASSINI~, G.BELLIA~~‘~, D.BERTINI’, J.BIELCIK’, M.B~HMER”, C.BO~ANO*, H.BOKEMEYER’, J.L.BoYARD”, SBRAMBILLA~, P.BRAUN-MUNZJNGER’, S.CHERNENKO’~, R.CONIGLIONE~, M.DAHLINGER’, H.DAuEs~, R.Dm4, F.DOHRMANN’~, I.DuRAN’, TH.EBERL”, L.FABBIE~I”, O.FATEEV”, CFERNANDEZ’, P.FINOCCHIARO~, JFRIESE”, IFR~HLICH’~, B.FUENTES’, J.A.GAR~oN’, BGENOLJNI”, RGERNHAUSER”, M.GOLUBEVA”, D.GONZALE?, H.GORINGER’, E.GRossE’~, F.GLJBER”, J.HEHNER’, TH.HENNINO”, S.HLAVAC~, J.HOFFMANN’, R.HOL~MANN’, J.HOMOLKA”, A.~ERUSALIMOV”, I.IoRI~,~~, M.JASKULA’, B.K.&MPFER’~, KKANAKI”, T. KARAVICHEVA’~, D. KIRSCHNER’~, L.KID~N’, PKIENLE”, I.KOENIG’, W.KOENIG’, H-J.K~RNER”, B.W.KOLB’, U.Kop$, R.KoTTE’~, W.K~HN”, T.KURTUKL~N’, RKROCKEN’~, R.KUIESSA’, A.KUREPIN”, J.LEHNERT’~, E.LINs’~, D.MAGESTRO’, P.MAIER-KOMOR”, CMAIOLINO~, J.MARKERT’~, V.METAG’~, J.MousA”, M.MONCH”, C.MONTZ’~, L.NAUMANN’~, A.NEKH&‘, W.NIE~UR~, W.OT?, R.NOVOTNY’~, J.O~wwows~~~, YU.PANEBRATSEV”, V.PECHENOV”, M.PETRI’~, P.PL~~ELLI~, J.~IETRASZKO’, R.PLESKAC’, M.PLOSKON’, ~.PRZYCXIDA’, NRABIN”, BRAMSTEIN”, A&~HETIN”, JRITMAN’~, P.ROSIER”, M.RoY-STEPHAN”, A.RUSTAMOV’, J.SABIN~, A.SAD~VSKI’~, B.SAILER”, PSALABURA’, M.SANCHEZ~, PSAPIENZA~, PSENGER’, CSCHROEDER’, K.SHILEEV”, PSHISHOV”, RSIMON’, V.SMOLIANKIN”, LSMYKOV”, S. SPATARO~, H.STELZER’, H.STR~BELE’~, J.STROTH’~, C.STURM’, M.SUDOL’ ,A.TARANENKO’, P.TLUSTY’, A.ToL&‘~, M.TRAXLER’~, H.TSERTOS’~, I.Tu~zo~, D.~ASSILIEV”, A.VA~QUEZ’, V.WAGNER’, W.WALUS’, S.WINKLER”, M.WISNIOWSKI’, T.WOJCIK~, J.WOSTI?NFELD’~, N.YAHLALI~, YU.?!ANEVSKY’~, K.~EITELHACK”, D.ZOVINEC~, P.~UMBRUCH’

The HADES data from p+Nb collisions at center of mass energy of $\sqrt{s_{NN}}$= 3.2 GeV are analyzed by employing a statistical model. Accounting for the identified hadrons $π^0$, $η$, $Λ$, $K^{0}_{s}$, $ω$ allows a surprisingly good description of their abundances with parameters $T_{chem}=(99\pm11)$ MeV and $μ_{b}=(619\pm34)$ MeV, which fits well in the chemical freeze-out systematics found in heavy-ion collisions. In supplement we reanalyze our previous HADES data from Ar+KCl collisions at $\sqrt{s_{NN}}$= 2.6 GeV with an updated version of the statistical model. We address equilibration in heavy-ion collisions by testing two aspects: the description of yields and the regularity of freeze-out parameters from a statistical model fit. Special emphasis is put on feed-down contributions from higher-lying resonance states which have been proposed to explain the experimentally observed $Ξ^-$ excess present in both data samples.

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 $1.04$ x $10^{-3}$ on the $3σ$ level is derived. Comparing this value with the number of successfully reconstructed $Λ$ hyperons allows to determine an upper limit on the ratio $N_{_Λ^3H}/N_Λ$, which is confronted with statistical and coalescence-type model calculations.

The HADES spectrometer installed at GSI Darmstadt is a second generation experiment to study production of lepton pairs from proton, pion and nucleus induced reactions at the SIS/BEVALAC energy regime. The HADES study of the light C+C system at 1 and 2 AGeV confirms former finding of the DLS collaboration. Further studies of the reaction p+p and d+p allowed to reveal contribution to the above mentioned data of di‐leptons produced during first chance collision. Finally, the results of the study of heavier system Ar+KCl indicates possible nonlinear dependence of the observed excess over the known long lived sources of di‐leptons on the number of participants.

Currently, the HADES spectrometer undergoes un upgrade program to be prepared for measurements at the upcoming SIS-100 synchrotron at FAIR. We describe the current status of the HADES di-electron measurements at the SIS-18 and our future plans for SIS-100.

In pp collisions at 1.25 GeV kinetic energy, the HADES collaboration aimed at investigating the di-electron production related to $Δ$ (1232) Dalitz decay ($Δ^+ \to pe^+e^-$). In order to constrain the models predicting the cross section and the production mechanisms of $Δ$ resonance, the hadronic channels have been measured and studied in parallel to the leptonic channels. The analyses of $pp\to npπ^+$ and $pp\to ppπ^0$ channels and the comparison to simulations are presented in this contribution, in particular the angular distributions being sensitive to $Δ$ production and decay. The accurate acceptance corrections have been performed as well, which could be tested in all the phase space region thanks to the high statistic data. These analyses result in an overall agreement with the one-$π$ exchange model and previous data.

Results of a study of charged pion production in 12C+12C collisions at incident beam energies of 1A GeV and 2A GeV, and 40Ar+natKCl at 1.76AGeV, using the spectrometer HADES at GSI, are presented. We have performed a measurement of the transverse momentum distributions of pi+- mesons covering a fairly large rapidity interval, in case of the C+C collision system for the first time. The yields, transverse mass and angular distributions are compared with a transport model as well as with existing data from other experiments.

The production of e+e- pairs in $^{12}C+^{12}C$ collisions at 1 GeV/u was investigated with the HADES experiment at GSI, Darmstadt. In the invariant-mass region $ 0.15\: GeV/c^{2} \leq M_{ee} \leq 0.5\: GeV/c^{2}$ the measured pair yield shows a strong excess above the contribution expected from hadron decays after freeze-out. The data are in good agreement with the results of the former DLS experiment for the same system and energy.

The High‐Acceptance Di‐Electron Spectrometer installed at GSI Darmstadt is a second generation experiment to study production of dielectron pairs from proton, pion and nucleus induced reactions at the SIS/BEVALAC energy regime. During period 2002–4 medium‐resolution data have been taken with HADES on the light C+C system at 1 and 2 AGeV. The data analysis confirms former finding of the DLS collaboration. First physics run on slightly heavier system Ar+KCl was carried out will almost full HADES setup at 2005.

The High Acceptance DiElectron Spectrometer (HADES) at GSI, Darmstadt, is investigating the production of e+e- pairs in A+A, p+A and N+N collisions. The latter program allows for the reconstruction of individual sources. This strategy will be roughly outlined in this contribution and preliminary pp/pn data is shown.

The HADES (High Acceptance Di-Electron Spectrometer) is a tool designed for lepton pair (e+e-) spectroscopy in pion, proton and heavy ion induced reactions in the 1-2 A GeV energy range. One of the goals of the HADES experiment is to study in-medium modifications of hadron properties like effective masses, decay widths, electromagnetic form factors etc. Such effects can be probed with vector mesons (ρ, ω, Φ) decaying into e +e- channel. The identification of vector mesons by means of a HADES spectrometer is based on invariant mass reconstruction of e +e- pairs. The combined information from all spectrometer sub-detectors is used to reconstruct the di-lepton signal. The recent results from 2.2 GeV p + p, 1 A GeV and 2 A GeV C+C experiments are presented.

HADES is a second generation experiment designed to study dielectron production in proton, pion, and heavy ion induced reactions at the GSI accelerator facility in Darmstadt. The physics programme of HADES is focused on in-medium properties of the light vector mesons. In this contribution we discuss relevance of dielectron spectroscopy to the problem of hadron mass origin. We present status of the HADES experiment, demonstrate its capability to identify rare dielectron signal and show first experimental results obtained from C+C reactions at 2 AGeV.

The HADES spectrometer installed at GSI Darmstadt is devoted to the study of the production of di-lepton pairs from vector meson decays in relativistic nucleus-nucleus collisions, as well as proton- and pion-induced reactions. Extraction of rare lepton pairs in high hadron multiplicity events requires an efcient particle identication (PID). In HADES charged particles momentum is measured by a tracking system surrounding the toroidal super conducting magnet, and velocity and energy loss is provided by a TOF detector. Leptons are identied by a Rich as well as a Shower detector. The particle identication method is using full experimental information from all subdetectors. To demonstrate the method performance, single particle spectra of charged hadrons and leptons from C+C at 2A GeV will be presented and compared with results of corresponding simulations. The proton and pion yields an mT and rapidity distributions will be compared with existing data. Very preliminary results of lepton analysis will be shown as well. © Institute of Physics, SAS, Bratislava, Slovakia.

The high-acceptance dielectron spectrometer (HADES) has become operational at GSI Darmstadt. The primary physics programme is to study in-medium changes of light vector mesons via their e+e− decays. The methods of dilepton signal reconstruction in the HADES spectrometer and preliminary dilepton spectra for C+C reactions at 2 A GeV are presented. In the signal reconstruction, particularly important is the reduction of the huge combinatorial background arising from e+e− combinations of leptons from gamma conversion in materials with other leptons in the collision. The purity of the dilepton signal is determined by using GEANT simulations with the full HADES geometry and a realistic detector response.

The identification of the light mesons in the HADES spectrometer is based on an invariant mass reconstruction of their decay into e + e - pairs. In the dilepton (e + e - ) signal reconstruction, particularly important is the reduction of a huge combinatorial background arising from wrong combinations of e + and e - to unlike sign pairs. Methods of the dilepton signal and combinatorial background reconstruction in the HADES spectrometer will be presented.

A novel system for data capture and processing from radiation detectors in the fields of X-ray crystallography and medical radiology has been developed. In its first version the system includes a custom made mixed analog-digital 16-channel VLSI circuit in 50 /spl mu/m pitch. Each channel comprises a charge amplifier, a shaper and a 21 bit counter. The circuit can be scaled in a daisy chain configuration. Data acquisition is performed with a custom made PCI card while the software is developed with visual C++ in MS Windows environment. Performance of a fully operational system, in terms of electronics noise and data capture speed is presented.