Abstract
We analyze the rapidity and transverse momentum dependence for the cumulants of the net-proton and net-baryon distributions in Au+Au collisions at $\sqrt{s_{\text{NN}}} = 5\,\text{GeV}$ with a microscopic hadronic transport (JAM) model. To study the effects of mean field potential and softening of equation of state (EoS) on the fluctuations of net-proton (baryon) in heavy-ion collisions, the calculations are performed with two different modes. The softening of EoS is realized in the model by implementing the attractive orbit in the two-body scattering to introduce a reduction pressure of the system. By comparing the results from the two modes with the results from default cascade, we find the mean field potential and softening of EoS have strong impacts on the rapidity distributions ($\text{d}N/\text{d}y$) and the shape of the net-proton (baryon) multiplicity distributions. The net-proton (baryon) cumulants and their ratios calculated from all of the three modes are with similar trends and show significant suppression with respect to unity, which can be explained by the presence of baryon number conservations. It indicates that the effects of mean field potential and softening of EoS might be not the ingredients that are responsible to the observed strong enhancement in the most central Au+Au collisions at 7.7 GeV measured by the STAR experiment at RHIC.
Highlights
One of the main interests of relativistic heavy ion collision experiments is to explore the phase structure of the QCD matters
This observation cannot be described by the UrQMD and AMPT model [30,31,32,33,34], both of which are transport model without mean field and QCD phase transition. This motivates us to investigate whether the large increase in the forth order net-proton fluctuations are caused by non-critical contributions, such as mean field potentials, which may play an important role at low collision energies and high baryon density region
To avoid the effects of auto-correlation, the collision centralities in the simulation are determined by the multiplicities of charged pion and kaon within pseudorapidity |η| < 1 in Au+Au collisions, which is applied for the data analysis of the net-proton fluctuation in the STAR experiment [13]
Summary
One of the main interests of relativistic heavy ion collision experiments is to explore the phase structure of the QCD matters. Striking observation is the large deviation above unity of the√net-proton κσ in the most central Au+Au collisions at sNN = 7.7 GeV, which is consistent with receiving strong positive critical contribution predicted by theoretical calculations This observation cannot be described by the UrQMD and AMPT model [30,31,32,33,34], both of which are transport model without mean field and QCD phase transition. This motivates us to investigate whether the large increase in the forth order net-proton fluctuations ( κσ2) are caused by non-critical contributions, such as mean field potentials, which may play an important role at low collision energies and high baryon density region. We will summarize our studies in the section V
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