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HADES is a versatile magnetic spectrometer aimed at studying dielectron production in pion, proton and heavy-ion-induced collisions. Its main features include a ring imaging gas Cherenkov detector for electron-hadron discrimination, a tracking system consisting of a set of 6 superconducting coils producing a toroidal field and drift chambers and a multiplicity and electron trigger array for additional electron-hadron discrimination and event characterization. A two-stage trigger system enhances events containing electrons. The physics program is focused on the investigation of hadron properties in nuclei and in the hot and dense hadronic matter. The detector system is characterized by an 85% azimuthal coverage over a polar angle interval from 18° to 85° , a single electron efficiency of 50% and a vector meson mass resolution of 2.5%. Identification of pions, kaons and protons is achieved combining time-of-flight and energy loss measurements over a large momentum range ( 0.1 < p < 1.0 GeV/ c . This paper describes the main features and the performance of the detector system. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The HADES spectrometer at GSI (Darmstadt) is investigating the e + e - pair production in p+p, p+ A and A+ A collisions. In this contribution we would like to highlight the physics motivations and the experiments performed so far, focusing mainly on the first results coming from 12C + 12C collisions at 1 and 2AGeV, and on preliminary results from p+ p/ d+ p collisions at 1.25AGeV. [ABSTRACT FROM AUTHOR]

The HADES spectrometer and a time-of-flight detector based on long-sized (50–250 cm) scintillation counters are described. The detector is designed for identification of electrons, pions, and protons with momenta of 0.1–1.5 GeV/ c at a flight distance of 220–250 cm. The operating conditions are analyzed, and the requirements to the detector and counter design are formulated. The design of the counters and their arrangement in the spectrometer are considered. The results of experimental studies of such characteristics of long counters as the light attenuation length in a scintillator and temporal and spatial resolutions, dependeing on the location of the point of the particle’s hit on the counter, are presented. Analysis of the data has shown that the main factor determining the spatial resolution of long counters is the quality of the polishing of the side faces of the scintillators, which determines the effective (averaged over the scintillator side surfaces) coefficient of total internal reflection R. It is shown that, for R>-0.99, it is quite possible to achieve temporal and spatial resolutions of 100 ns and 2–3 cm, respectively, for scintillators with a length of up to 250 cm and a cross section of 1–20 cm2. Foreign and Russian photomultipliers were used in the counters. [ABSTRACT FROM AUTHOR]

The reactionTh( γ,f) is studied using bremsstrahlung γ-beams in the (5.45-6.85) MeV end point energy range. Fragments angular distributions are measured and yield components with opposite parities are separated. The unfolded cross sections have resonant behaviour which indicates the existence of low damped vibrational states. Furthermore, a near degeneracy for K=0 and K= 0 resonances at ∼5.5 MeV and ∼6 MeV is observed. Data are analysed in terms of a double humped barrier configuration within the doorway state model for fission. For each component maxima with almost equal heights and a shallow intermediate minimum are determined. Moreover almost equal potential barriers with K=0 and opposite parities are found. This is a signature for mass-asymmetric shapes and seems a clear indication for a threehumped barrier configuration with a low inner maximum and a third mass asymmetric shallow minimum due to the fragmentation of the normal mass-asymmetric second maximum. [ABSTRACT FROM AUTHOR]

The event-by-event determination of the impact parameter from particle multiplicity emitted in heavy-ion collisions is considered. The associate problem of the determination of the particle multiplicity on both multi-event and event-by-event basis is formulated and discussed. It is shown that a multi-event data analysis procedure allows an accurate determination of the multipolicity distribution of the emitted particles even with not necessarily large total efficiency and granularity detection systems. In the event-by-event data analysis procedure a fold-to-multiplicity conversion based on the Bayes strategy is adopted. It is shown that a reliable event-by-event multiplicity determination and multiplicity resolution definition cannot prescind from a multi-event analysis of the full data set. It is found that the resolution of the event-by-event fold-to-multiplicity conversion procedure depends on the characteristics of the detection system, but not exclusively. The dependence on the particular multiplicity distribution investigated is discussed. It is concluded that event-by-event high-resolution impact parameter measurements can only be performed with very efficient and granular detection systems, but a gross event classification into central and peripheral collisions can be performed even with detection efficiency as low as Ω=0.3. [ABSTRACT FROM AUTHOR]

Copyright of Il Nuovo Cimento: A is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Il Nuovo Cimento: A is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Il Nuovo Cimento: A is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The emission of hard photons and pre-equilibrium protons has been investigated in exclusive experiments performed with MEDEA detector. The observation of the γ-proton anticorrelation indicates that the dominant production mechanism is the first-chance neutron-proton (np) collisions. The anisotropic angular distributions point out the presence of screening effects and are reminiscent of the free np scattering thus giving information of the space-time origin of the energetic protons. Protons, with energy more than twice the kinematical limit for nucleon-nucleon (NN) collisions, have been observed in several reactions around the Fermi energy. [ABSTRACT FROM AUTHOR]

Photons emitted in the Si+ Ni and S+ Ni reactions at 143 MeV and 156 MeV incident energy respectively, have been detected in coincidence with the ejected charged fragments. An array of 48 BaF γ-rays detector and 6 solid state silicon detector telescopes have been used. Photon energy spectra measured in the energy range from 2 to 20 MeV in coincidence with ejectiles coming from deep inelastic reactions, are consistent with statistical emission from the reaction products. [ABSTRACT FROM AUTHOR]

The HADES spectrometer at GSI (Darmstadt) is investigating the e + e - pair production in p+p, p+ A and A+ A collisions. In this contribution we would like to highlight the physics motivations and the experiments performed so far, focusing mainly on the first results coming from 12C + 12C collisions at 1 and 2AGeV, and on preliminary results from p+ p/ d+ p collisions at 1.25AGeV. [ABSTRACT FROM AUTHOR]