Speaker
Description
The equation of state of nuclear matter at 2-4 times nuclear saturation density is not very well determined by first principle methods. Heavy-ion collisions offer the opportunity to reach those high densities and collective flow measurements are sensitive to the properties of the medium. At 1-2 AGeV per nucleon beam energy transport approaches are the best choice for the theoretical description of the dynamic evolution of the system. In this work, we aim to constrain the equation of state of nuclear matter by comparing calculations within the SMASH transport approach to directed and elliptic flow measurements for protons and deuterons performed by the FOPI and HADES collaboration in a systematic way.
A momentum-dependent term is included in the potential for which we show that it is needed to describe flow data. We further incorporate a simple symmetry potential in the transport model and present constraints on the stiffness of the equation of state of nuclear matter at saturation density and on the symmetry potential. For the FOPI data, Z=1 nuclei are considered and differential directed and elliptic flow measurements are compared with the calculations using a chi-square analysis. For Au+Au collisions at 1.23 AGeV, the HADES measurements, the constraints are obtained by performing a Bayesian analysis such that we can also provide an uncertainty for the estimated parameters. The posterior distribution is obtained by Markov chain Monte Carlo sampling for which we emulate the transport model with a Gaussian process to lower computational costs. We find that a relatively stiff equation of state is favoured in our analysis with a small uncertainty whereas the constraints obtained for the symmetry potential are rather loose. For the lower FOPI energy of Au+Au collisions at 0.4 AGeV a softer equation of state yields a better description of the collective flow data. This potential discrepancy can be attributed to the role of resonance excitations that effectively soften the equation of state of the formed medium in higher energy collisions.
See https://arxiv.org/abs/2405.09889 and https://arxiv.org/abs/2409.16927
| Category | Theory |
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