Centrality Dependence of Bulk Fireball Properties at RHIC

We explore the centrality dependence of properties of the dense hadronic matter created in \mathversion{bold}{$\sqrt{s_{NN}}=200$}\,GeV Au--Au collisions at RHIC. Using the statistical hadronization model we fit particle yields known for 11 PHENIX centrality bins and using STAR yields for $\phi$ and $K^*$. We present the resulting centrality dependence of model parameters $T,\mu_{\rm B},\mu_{\rm S}, $\gamma_s$, the rapidity yields of physical quantities and the physical properties of bulk matter at hadronization. The most remarkable finding of this study is the recognition that the bulk properties $P$ pressure, $\epsilon$ energy density, $\sigma$ of the hadronizing dense matter fireball created at RHIC do not depend on the size of the system for $A\gtrsim 20 $, where $A$ is the number of reaction participants. For most central collisions the strangeness per entropy yield $s/S=(2.9\pm0.3)10^{-3}$ is more than 4 times enhanced compared to the AGS energy scale. For the most peripheral reactions this ratio is $s/S=(1.9\pm0.3)10^{-3}$ which shows the influence of the fireball expansion dynamics on production of strangeness. We see this in the steady rise of strangeness occupancy $\gamma_s$ with centrality. The baryon end entropy density per unit rapidity grows also with centrality and we find in most central 5\% collisions $d(B-\overline B)/dy=14\pm2$, the strangeness yield $ds/dy=135\pm10$ and the entropy yield $dS/dy=4900\pm400$.