Speaker
Description
We present some results of analysis of hadron production in $pp$ and $AA$ collisions obtained in the framework of $z$-scaling and discuss a possible signatures of a phase transition in nuclear matter. This approach allows to systematically analyze experimental data on inclusive cross sections over a wide range of the collision energies, multiplicity densities, transverse momenta, and angles of various particles. The concept of the $z$-scaling is based on the principles of self-similarity, locality and fractality reflecting general features of particle interactions. The self-similarity variable $z$ is a function of the momentum fractions $x_1$ and~$x_2$ of the colliding objects carried by interacting hadron constituents and depends on the fractions $y_a$ and $y_b$ of the scattered and recoil constituents carried by the inclusive particle and its recoil counterpart. The scaling function $\psi(z)$ is expressed via inclusive cross-section, multiplicity density and three model parameters. Structure of the colliding objects and fragmentation processes is characterized by the structural and fragmentation fractal dimensions $\delta$ and $\epsilon$, respectively.
The produced medium is described by a "specific heat" $c$.
The energy and centrality dependence of $K_S^0$-meson spectra measured by the STAR Collaboration at RHIC in $Au+Au$ collisions over a wide range of $\sqrt {s_{NN}} =7.7-200$~GeV was studied in the $z$-scaling approach. The scaling function $\psi(z)$ was constructed and the self-similarity of $K_S^0$-meson production was confirmed. Anomalous behavior of "specific heat" $c_{AuAu}$ and fractal entropy in dependence of collision energy was found. The non-trivial dependence of $c_{AuAu}$ on the collision energy shows that $K_S^0$ meson is much more sensitive to properties of nuclear medium than a non-identified negative hadron A non-trivial dependence of fractal entropy $S_{\delta ,\epsilon}$ on the collision energy with decreasing $p_T$ was found. It reflects the irregularity of the behavior of the specific heat $c_{AuAu}$. The irregularities in the behavior of specific heat parameter $c_{AuAu}$ and fractal entropy $S_{\delta , \epsilon}$ considered as a possible indication of phase transition in nuclear matter are discussed.
