Relativistic Heavy Ion Collisions
High Acceptance Di-Electron Spectrometer
Experimental Summary
Investigation of hadron properties inside nuclear matter at normal and high densities and temperatures is one of the main goals of current nuclear physics studies. Heavy-ion, pion, and proton-induced reactions on heavy nuclei in a 1-3.5 GeV kinetic beam energy region are the proper tool to probe particle properties in the long-living dense state of nuclear matter. The matter created in such collisions differs from the one studied at the SPS, RHIC, or the LHC because it consists mainly of baryons (nucleons and their excited states - baryon resonances) and contains a small number of mesons only. This matter can be compressed up to 3 times nuclear-matter density for about 10-12 fm/c. Di-electron pairs originating from in-medium hadron decays and rare strange hadrons (kaons, hyperons) are the main probes measured in the experiment. Since conclusions on in-medium effects rely strongly on the understanding of hadron properties in the vacuum, a complementary program focusing on e+e-, kaon, and hyperon (Σ, Λ) production in nucleon-nucleon collisions is needed.
To investigate the properties of hadrons in hot and dense nuclear matter, the electron-positron pair spectrometer HADES (High Acceptance Di-Electron Spectrometer) was built at the GSI (Helmholtzzentrum für Schwerionenforschung) Darmstadt (Germany). The detector is operated by an international collaboration of 17 institutions from 9 European countries. It is optimized for the detection of electrons and positrons exploiting a RICH (Ring Imaging Cherenkov) detector subsystem. At the same time, HADES is a very efficient spectrometer of all charged particles like protons, pions, kaons, etc. The SIS18 accelerator facility provides beams of relativistic heavy ions and protons, as well as a secondary pion beam.
Members of our group actively participate in data analysis, paper writing, proposals of new experiments, etc. Our main research interests concern the reconstruction of mesons decaying into di-electron or pion pairs, flow studies, etc. In addition, our group was involved in the construction and is involved in the operation of three HADES detector subsystems:
- A large (~5 meters high) wall consisting of 384 scintillation rods (up to 2.5 meters long) Time-of-flight system (TOF). Its purpose is to measure the time of flight of charged particles with a very high precision of about 100 ps and provide thus crucial input for particle indentification.
- A smaller Forward Wall (FW hodoscope) consisting of 380 square scintillation detectors covering small polar angles. This detector determines reaction plane and collision centrality.
- A new detector ECAL (Electromagnetic Calorimeter). This is a large wall consisting of 978 lead-glass modules. The role of ECAL is to identify and determine the energy of neutral particles like pions and eta mesons via their two-photon decay. The mass and energy of neutral particles can be computed from the energies and directions of photons detected in lead-glass modules. The construction of ECAL was finished in 2023.
The spectrometer HADES has been operated since 2018 in the framework of the newly built Large Research Infrastructure FAIR (Facility for Antiproton and Ion Research), which is an ESFRI landmark (European Strategy Forum on Research Infrastructures) located at the GSI.
Team members of the HADES experiment:
Research scientists:
Andrej Kugler (head of the group)
Pavel Tlustý
Ondřej Svoboda
Vladimír Wagner
Ph.D. students:
Antonín Opíchal
Contact person:
Andrej Kugler, kugler@ujf.cas.cz
The phase diagram in the region of high baryonic density and a rather low temperature is expected to show a rich structure that involves first order phase transition between hadronic and partonic matter terminated by a critical point, or new phases of matter such as the anticipated quarkyonic matter. The proof of the existence of such structures would be a breakthrough in our understanding of the strong interaction. Therefore it is a main goal of many research activities in high-energy heavy-ion physics. This research is linked as well with the verification of the models, which attempt to describe the fusion of neutron stars generating gravitational waves observed recently (Nobel Prize 2017) as well as to understanding supernova explosions. The experiments HADES and CBM in the Nuclear Matter Physics pillar of the newly built Large Research Infrastructure FAIR (Facility for Antiproton and Ion Research) will play a unique role in constraining the equation-of-state of nuclear matter at neutron-star core densities. CBM is designed to take data at unique high reaction rates - up to 10 MHz. This is crucial for achieving the required precision during multi-differential measurement of rare probes such as multi-strange hyperons, charmed particles, and vector mesons, which are sensitive to the dense phase of the fireball created during the heavy-ion collision. Most of these measurements will be carried out for the first time in the energy domain 1-10 GeV/nucleon available at the SIS100 accelerator of FAIR.
Our group is involved in design and construction of FSD (Forward Spectator Detector) and in tests of its prototypes. The FSD will measure main characteristic features of heavy ion collisions like centrality, reaction plane and directed flow. FSD is one of detector subsystem of CBM. It will be placed at distance of about 8 m from the target and will detect projectile spectators, i.e. noninteracting nucleons and fragments emitted forward at low polar angels. The FSD will be located very close to the beam line and therefore high intensity beam will result in very high radiation dose. Our group is exploiting neutron source at NPI cyclotron to carry out test of radiation hardness of corresponding components and test if they stay operational up to 3×1012 n/cm2. We are participating also on R&D of other aspects of FSD, simulations of directed flow measurement by FSD, tests of FSD scintillator modules, construction of support frame for FSD together with our colleagues from Czech Technical University etc.
Further, our group contributes to the FAIR infrastructure related to CBM. In particular, we designed and provided a special Upstream platform for the HADES and CBM detectors. The weight of the platform itself is about 40 tons and it has to bear a load of more than one hundred tons of the detectors and devices that will be located on the platform. The platform has a footprint of 14 m x15 m and it was produced by a Czech firm and installed during spring 2023 in the new CBM cave. For the CBM, we designed and provided a downstream carbon beampipe. We also plan to provide vacuum elements for the HEBT (High Energy Beam Transport) line, which has to deliver the beam from the future SIS100 accelerator to the CBM cave.
Team members of the CBM experiment:
Research scientists:
Andrej Kugler
Ondřej Svoboda
Contact person:
Andrej Kugler, kugler@ujf.cas.cz