Speakers
Description
In March 2025, at the GSI laboratory in Germany, the ASY-EOS II experiment was conducted. The reaction ^{197}Au+^{197}Au was studied at beam energies of 280, 400, 600, and 1000 AMeV. The experiment was designed to investigate high-density nuclear matter and to provide a new and robust constraint on the symmetry energy term of the nuclear equation of state (EoS).
Understanding the behavior of the symmetry energy as a function of density is indeed essential for the interpretation of numerous phenomena, both of nuclear and astrophysical nature. The experimental setup consisted of several detectors; among these, four double rings of the CHIMERA multidetector, transported from the INFN–Laboratori Nazionali del Sud (LNS) to GSI, were employed in combination with the KRAB detector for the reconstruction of the reaction plane and for event centrality selection. Moreover, the experimental setup included the TOFD detector, consisting of two frames: one positioned along the beam direction and one positioned sideways at approximately 50 degrees with respect to it. The first one was used for selecting the reaction centrality through the determination of suitable global variables. The second frame, placed geometrically in
correspondence with the NeuLAND detector, was instead used as a veto for charged particles. NeuLAND, with its 26 planes and a total depth of about 1.3 meters, enabled excellent separation between protons and other hydrogen isotopes. This represents a significant improvement over the previous ASY-EOS experiment.
Thanks to these capabilities, neutron–proton observables, such as the elliptic flows of neutrons and protons, can be determined with high precision. In particular, the ratio of neutron to proton elliptic flows is one of the most sensitive observables to the symmetry energy, up to densities of about 2 \rho_{0} (rho_{0} \sim 0.17 nucleons/fm^{3}). Preliminary results of the data analysis will be presented, with particular focus on the calibration of the TOFD veto and NeuLAND detectors and the discrimination between neutrons and protons/charged particles.