Speaker
Description
The Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany is a next-generation accelerator facility designed to explore the properties of strongly interacting matter at extreme conditions of temperature, density, pressure, and isospin. One of its central goals is to constrain the nuclear matter equation of state (EOS) which is key to understanding the QCD phase diagram and astrophysical phenomena like neutron stars and supernovae.
At FAIR, a suite of complementary experiments — CBM, HADES, NUSTAR, and their hypernuclear programs — aim to constrain the EOS across a wide range of densities and temperatures.
The HADES (High Acceptance Di-Electron Spectrometer) and CBM (Compressed Baryonic Matter) experiments are designed to explore the behavior of strongly interacting matter at high baryon densities and moderate temperatures, using high-energy heavy-ion collisions. HADES complements the CBM setup by operating at lower beam energies and/or lighter systems. Both experiments focus on observables that are sensitive to the pressure-density relation of nuclear matter, such as collective flows, particle yields, and fluctuations of conserved charges. A crucial feature of both CBM and HADES is potential to detect dileptons. These leptonic probes carry undistorted information from the hot and dense states of the collision and provide insight into the in-medium properties of vector mesons. Those observables contribute to constrain the temperature and density evolution in the course of the collision.
The NUSTAR (Nuclear Structure, Astrophysics and Reactions) collaborations explore the EOS at all densities with a particular focus on the low-density, cold but highly asymmetric regime by studying exotic, neutron-rich nuclei far from stability. Key observables like two-neutron removal cross sections and dipole polarizability allow deducing the thickness of neutron skins. Neutron skins as well as high precision measurements of nuclear masses help to constrain the symmetry energy of the EOS and its slope, which are key ingredients for understanding the structure of neutron stars and the crust-core transition.
Additionally, FAIR’s hypernuclear program — pursued through CBM/HADES and NUSTAR — explores the role of strangeness in dense matter. Observables from single and double hypernuclei provide empirical constraints on hyperon-nucleon and hyperon-hyperon interactions, which become significant in the high-density interiors of neutron stars. The presence of hyperons tends to soften the EOS, reducing the maximum mass of neutron stars — a feature known as the "hyperon puzzle”. Precision hypernuclear studies help to resolve this puzzle by providing constraints at or below saturation densities. Novel observables like hyperon collective flow might give access to the hyperon-nucleon potential at higher densities.
In summary, the combination of CBM/HADES and NUSTAR at FAIR enables a comprehensive, multi-faceted exploration of the nuclear matter EOS. Each experiment probes a different regime of density, temperature, and isospin, collectively building a coherent picture of how matter behaves under such extreme conditions.
| Presentation Style | Invited Speaker |
|---|