Chemical Freeze-out Parameters via a Non-perturbative QCD Approach

By analyzing the calculated baryon number susceptibility ratios ${\chi }_1^B\mathrm{/}{\chi }_2^B$ and ${\chi }_3^B\mathrm{/}{\chi }_1^B$ in two-flavor system via the Dyson-Schwinger equation approach of QCD, we determine the chemical freeze-out temperature and baryon chemical potential in cases of both thermodynamic limit and finite size. We calculate the center-of-mass energy dependence of the ${\chi_{4}^{B}}/{\chi_{2}^{B}}, (\kappa \sigma^{2})$ at the freeze-out line and find an excellent agreement with experimental data in $\sqrt{S_{NN}^{}}\ge 19.6$GeV region when taking into account the finite size effect. Our calculations indicate that the $\kappa \sigma^{2}$ exhibits a non-monotonic behavior in lower collision energy region.