Model dependence of isospin sensitive observables at high densities

Abstract

Within two different frameworks of isospin-dependent transport model, i.e., Boltzmann-UehlingUhlenbeck (IBUU04) and Ultrarelativistic Quantum Molecular Dynamics (UrQMD) transport models, sensitive probes of nuclear symmetry energy are simulated and compared. It is shown that neutron to proton ratio of free nucleons, π − /π + ratio as well as isospin-sensitive transverse and elliptic flows given by the two transport models with their "best settings", all have obvious differences. Discrepancy of numerical value of isospin-sensitive n/p ratio of free nucleon from the two models mainly originates from different symmetry potentials used and discrepancies of numerical value of charged π − /π + ratio and isospin-sensitive flows mainly originate from different isospin-dependent nucleon-nucleon cross sections. These demonstrations call for more detailed studies on the model inputs (i.e., the density-and momentum-dependent symmetry potential and the isospin-dependent nucleon-nucleon cross section in medium) of isospin-dependent transport model used. The studies of model dependence of isospin sensitive observables can help nuclear physicists to pin down the density dependence of nuclear symmetry energy through comparison between experiments and theoretical simulations scientifically.

Results of the ASY-EOS experiment at GSI: The symmetry energy at suprasaturation density

“…The latter have recently been investigated in nuclei [67,68] and their consequences for transport descriptions of intermediate-energy heavy-ion reactions are of high interest and need to be investigated [72]. Moreover, it will be quite important to compare the experimental data with the predictions of several transport models, of both Boltzmann-Vlasov and moleculardynamics type [94], in order to pursue the work towards a model-independent constraint of the high-density symmetry energy initiated in Ref. [14].…”

Nuclear Symmetry Energy Extracted from Laboratory Experiments

“…8. While at supra-saturation densities the data is very limited and transport model calculations of reaction observables are still rather model dependent [103][104][105][106]. For example, analyzing the π − /π + data from the FOPI/GSI collaboration [86,107] using a BUU-type (Boltzmann-…”

Decomposition of the sensitivity of the symmetry energy observables

“…The latter has been studied for decades due to its great importance in both nuclear physics and astrophysics [2][3][4][5][6][7][8][9][10]. Although significant progress has been made, the symmetry energy is still subject to uncertainties especially at high-density region [11,12]. Nowadays, many sensitive observables have been identified as promising probes of the symmetry energy, such as the π − /π + ratio [13][14][15][16][17][18][19], energetic photon as well as η [20][21][22], the neutron to proton ratio n/p [23][24][25], t/ 3 He [26,27], the isospin fractionation [24,[28][29][30] and the neutron-proton differential flow [31,32].…”