5th International Symposium on Nuclear Symmetry Energy NuSYM15, June 29 - July 2, 2015 Kraków, POLAND

Paolo Russotto
INFN-Sezione di Catania, ITALY

### The ASY-EOS experiment at GSI: investigating symmetry energy at supra-saturation densities

P. Russotto for ASY-EOS collaboration

Abstract
The elliptic-flow ratio of neutrons with respect to protons or light complex particles in reactions of heavy-ions at pre-relativistic energies is proposed as an observable sensitive to the strength of the symmetry term in the nuclear equation of state at supra-saturation densities. The results obtained from the existing FOPI/LAND data for $^{197}$Au+$^{197}$Au collisions at 400 MeV/nucleon in comparison with the UrQMD model favour a moderately soft symmetry term but suffer from a considerable statistical uncertainty [1]. These results have been confirmed by an independent analysis based on Tübingen QMD [2]. In order to obtain an improved data set for Au+Au collisions and to extend the study to other systems, a new experiment was carried out at the GSI laboratory by the ASY-EOS collaboration [3]. The flows of neutrons and light charged particles were measured for $^{197}$Au+$^{197}$Au, $^{96}$Ru+$^{96}$Ru and $^{96}$Zr+$^{96}$Zr collisions at 400 MeV/nucleon using the Large Area Neutron detector LAND, four double-rings of the forward part of the CHIMERA multi-detector, the ALADIN ToF-Wall, the KRATTA Si-CsI triple-telescope array and the Microball detectors. First results, including comparison of elliptic flow ratios with UrQMD calculations for Au+Au system, will be reported.

[1] P. Russotto et al., Phys. Lett. B 697 (2011) 471.
[2] M.D. Cozma, Phys. Lett. B 700, 139 (2011); M.D. Cozma et al., Phys. Rev. C 88, 044912 (2013).
[3] P. Russotto et al., Eur. Phy. J A 50, 38 (2014).