Hadron Production and Phase Changes in Relativistic Heavy Ion Collisions

We study soft hadron production in relativistic heavy ion collisions in a wide range of reaction energy, $4.8 {\rm GeV}<\sqrt{s_{\rm NN}}<200 {\rm GeV}$, and make predictions about yields of particles using the statistical hadronization model. In fits to existent data, we obtain both statistical parameters as well as physical properties of the hadron source. We identify the properties of the fireball at the critical energy threshold, $6.26 {\rm GeV}<\sqrt{s_{\rm NN}^{\rm cr}}<7.61 {\rm GeV}$, delineating for higher energies hadronization of an entropy rich phase. In terms of the chemical composition, one sees a phase which at low energy is chemically under-saturated, and which turns into a chemically over-saturated state persisting up to maximum accessible energy. Assuming then that there is no change in physical mechanisms in the energy range $15>\sqrt{s_{\rm NN}}\ge 200 {\rm GeV}$, we use continuity of particle yields and statistical parameters to predict the hadron production patterns at $\sqrt{s_{\rm NN}}=62.4 {\rm GeV}$, and to obtain total yields of hadrons at $\sqrt{s_{\rm NN}}=130$ and $200 {\rm GeV}$. We consider, in depth, the pattern we uncover within the hadronization condition, and discuss possible mechanisms associated with the identified rapid change in system properties at $\sqrt{s_{\rm NN}^{\rm cr}}$. We propose that the chemically over-saturated 2+1 flavor hadron matter system undergoes a 1st order phase transition.