Speaker
Description
The data [1] on spectra of $K_S^0$ mesons measured by the STAR Collaboration in $\rm Au+Au$ collisions at various centralities characterized by different multiplicity densities of negative particles were analyzed in the $z$-scaling approach [2,3]. The transverse momentum distributions obtained in the BES-I program at RHIC were accumulated in seven centrality classes from the most central $(0-5)\%$ to peripheral $(60-80)\% $collisions in the rapidity range $|y| < 0.5$. These data and the earlier STAR data at $\sqrt s_{NN} = 62, 130$ and $200$ GeV allow us a detail study of the energy and centrality dependence of $K_S^0$-meson production in a wide range of $\sqrt s_{NN} = 7.7–200$ GeV. The entropy of the microscopic configurations accompanied of $K_S^0$-meson production in $\rm Au+Au$ collisions, is constructed. It is expressed, in the $z$-scaling approach, via the momentum fractions of colliding particles and scattered constituents fragmented to produced particles, the structural and fragmentation fractal dimensions, the multiplicity density of negative particles and model parameter $c_{AuAu}$ interpreted as a specific heat of produced medium. The irregularity in the behavior of the specific heat parameter $c_{AuAu}$ was connected in [4] with existence of a phase transition in nuclear matter. The dependence of the entropy $\rm S$ on the collision energy $\sqrt s_{NN}$ over the range $7.7-200$ GeV for most central $(0-5)\%$ and peripheral $(60-80)\%$ events was studied as a function of transverse momentum of produced of $K_S^0$-meson. It was found that the values of the entropy in peripheral collisions at low $\sqrt s_{NN}$ are much smaller than in the central ones. Non-trivial dependence of $\rm S$ on the collision energy with decreasing $p_T$ was found. The entropy reaches a local maximum at the energy
$\sqrt s_{NN} = 11.5 - 19.6$ GeV for $p_T = 0.3$ GeV/c. This is followed by an abrupt fall of $\rm S$ at $\sqrt s_{NN} = 27 - 39$ GeV with a gradual increase at higher energies. Such anomalous behavior is also visible at $p_T = 0.6$ and $1.0$ GeV/c in the same energy range. At higher $p_T \ge $2 GeV/c, the entropy $\rm S$ becomes a monotonously increasing function of the collision energy and the observed anomaly of $\rm S$ disappears. The monotonic growth of $\rm S$ is seen for all $p_T$ in the peripheral collisions.
- J. Adam et al. (STAR Collaboration), Phys. Rev. C102,034909 (2020).
- M. Tokarev et al., Phys. Part. Nucl. 51, 141 (2020).
- M. Tokarev, A. Kechechyan, I. Zborovský, Nucl. Phys. A993, 121646 (2020).
- M. Tokarev, I. Zborovský, Nucl.Phys. A1025, 122492 (2022).
