About 10 μs after the Big Bang, the universe was filled—in addition to photons and leptons—with strong-interaction matter consisting of quarks and gluons, which transitioned to hadrons at ...temperatures close to kT = 150 MeV and densities several times higher than those found in nuclei. This quantum chromodynamics (QCD) matter can be created in the laboratory as a transient state by colliding heavy ions at relativistic energies. The different phases in which QCD matter may exist depend for example on temperature, pressure or baryochemical potential, and can be probed by studying the emission of electromagnetic radiation. Electron–positron pairs emerge from the decay of virtual photons, which immediately decouple from the strong interaction, and thus provide information about the properties of QCD matter at various stages. Here, we report the observation of virtual photon emission from baryon-rich QCD matter. The spectral distribution of the electron–positron pairs is nearly exponential, providing evidence for a source of temperature in excess of 70 MeV with constituents whose properties have been modified, thus reflecting peculiarities of strong-interaction QCD matter. Its bulk properties are similar to the dense matter formed in the final state of a neutron star merger, as apparent from recent multimessenger observation.
As a result of the LHC injectors upgrade after the Long Shutdown (2019-2020), the expected Pb-Pb luminosity and collision rate during the so called Runs 3 and 4 will considerably exceed the design ...parameters for several of the key ALICE detectors systems including the forward trigger detectors. Fast Interaction Trigger (FIT) will be the primary forward trigger, luminosity, and collision time measurement detector. It will also determine multiplicity, centrality, and reaction plane of heavy ion collisions. FIT is expected to match and even exceed the functionality and performance currently secured by three ALICE sub-detectors: the time zero detector (T0), the VZERO system (V0), and the Forward Multiplicity Detector (FMD). FIT will consist of two arrays of Cherenkov radiators with MCP-PMT sensors and of a single, large-size scintillator ring. Because of the presence of the muon spectrometer, the placement of the FIT arrays will be asymmetric: ∼800 mm from the interaction point (IP) on the absorber side and ∼3200 mm from IP on the opposite side. The ongoing beam tests and Monte Carlo studies verify the physics performance and refine the geometry of the FIT arrays. The presentation gives a short description of FIT, triggers and readout requirement for the ALICE Upgrade, a summary of the performance, and the outcome of the simulations and beam tests.
.
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.
Forward Diffractive Detector control system for Run 3 in the ALICE experiment Mejía Camacho, J.M.; Rodríguez Ramírez, S.A.; Cabanillas Noris, J.C. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
05/2023, Letnik:
1050
Journal Article
Recenzirano
The ALICE experiment went through major upgrades in preparation for Runs 3 and 4 at the CERN LHC, which foresee a significant increase in the data stream rate. To cope with it, a new Computing System ...Online–Offline (O2) was developed by ALICE and several detectors were upgraded. One of these upgrades corresponded to the ALICE Diffractive (AD) detector, which was replaced by the new Forward Diffractive Detector (FDD). A fundamental system that allows for recording of data as well as for the stable and safe operation of the experimental setup is the Detector Control System (DCS). The DCS controls, monitors, and configures detectors’ hardware and their subsystems among which are commercial hardware and specific custom equipment. In this work, we describe the implementation of the DCS of FDD, which was designed and developed using the SCADA commercial software WinCC Open Architecture (WinCC-OA®) and the Joint Controls Project (JCOP) Framework. We also describe the modeling of FDD-DCS as a finite state machine to be integrated into the ALICE Central DCS, and to be operated by DCS shifters in the run control center and, remotely, by detector experts. This new DCS was developed to comply with the new LHC operational standards that allow for processing the increased luminosity due to collisions at a higher energy, and for fulfilling the specific requirements of the ALICE experiment, in order to address the scientific challenges of its physics program.
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.
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 data on dielectron emission in proton induced reactions on a Nb target at 3.5 GeV kinetic beam energy measured with HADES installed at GSI. The data represent the first high statistics ...measurement of proton-induced dielectron radiation from cold nuclear matter in a kinematic regime, where strong medium effects are expected. Combined with the good mass resolution of 2%, it is the first measurement sensitive to changes of the spectral functions of vector mesons, as predicted by models for hadrons at rest or small relative momenta. Comparing the e+e− invariant mass spectra to elementary p+p data, we observe for e+e− momenta Pee<0.8 GeV/c a strong modification of the shape of the spectrum, which we attribute to an additional ρ-like contribution and a decrease of ω yield. These opposite trends are tentatively interpreted as a strong coupling of the ρ meson to baryonic resonances and an absorption of the ω meson, which are two aspects of in-medium modification of vector mesons.
.
The combination of a production target for secondary beams, an optimized ion optical beam line setting, in-beam detectors for minimum ionizing particles with high rate capability, and an efficient ...large acceptance spectrometer around the reaction target constitutes an experimental opportunity to study in detail hadronic interactions utilizing pion beams impinging on nucleons and nuclei. For the 0.4-2.0GeV/c pion momentum regime such a facility is located at the heavy ion synchrotron accelerator SIS18 in Darmstadt (Germany). The layout of the apparatus, performance of its components and encouraging results from a first commissioning run are presented.
PDF
