# Working Area 2: From collisions of heavy ions tocollisions of neutron stars

One of the main goals of ELEMENTS is the understanding of bulk properties of nuclear matter under extreme conditions. At high temperatures or high net baryon densities a new state of matter, a quark-gluon plasma, is formed. The nature of the transition between the ordinary hadron gas phase and the QGP phase is still under investigation, as well as the detailed properties of those phases. Heavy-ion collisions at varying beam energies allow to access large regions of this phase diagram of strongly-interacting matter. Within neutron star mergers very high densities and moderate temperatures are reached.

Detailed dynamical modeling

To gain insights on the properties of matter from observables in gravitational-wave signals and heavy-ion reactions, detailed dynamical evolution models are required. This is the core task of work area 2 to advance the description of heavy-ion collisions and neutron star mergers within magneto-hydrodynamics and transport approaches. The first neutron star merger events (GW170817 and GW190425) are providing first constraints on maximum masses, radii and tidal deformabilities. In heavy-ion collisions, the main observables include fluctuations and correlations of final particles, the vorticity measured through polarized particles, electromagnetic radiation as well as light nuclei production.

The following milestones have been formulated in work area 2:

• Extract stringent constraints on the nuclear equation of state of QCD matter at high net baryon densities based on HADES experimental data with a hadronic transport approach
• Construct a theoretical framework for spin-MHD and assess the impact on dynamics of heavy-ion collisions
• Build a most comprehensive set of merger models and calculate their impact on nucleosynthesis yields and kilonova light curve
• Achieve a quantitative understanding of the high density equation of state on the observables of binary neutron star mergers

Work area 2 will build a common framework to interpret neutron star mergers and heavy-ion collisions. One particular focus is the consistency of the equation of state between observables from neutron star mergers and heavy-ion reactions.

PIs in this work area include: A. Arcones, T. Aumann, A. Bauswein, H. Elfner, T. Galatyuk, G. Martinez-Pinedo, A. Obertelli, D. Rischke, L. Rezzolla, L. Sagunski, J. Stroth