Baryon-strangeness correlations in Au+Au collisions at $\sqrt{s_{\mathit{NN}}}=7.7–200$ GeV from the UrQMD model

Fluctuations and correlations of conserved charges are sensitive observables for studying the QCD phase transition and critical point in high-energy heavy-ion collisions. We have studied the centrality and energy dependence of mixed cumulants (up to fourth order) between net baryon and net strangeness in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathit{NN}}}=7.7$, 11.5, 19.6, 27, 39, 62.4, and 200 GeV from the ultrarelativistic quantum molecular dynamics (UrQMD) model. To compare with other theoretical calculations, we normalize these mixed cumulants by various order cumulants of net-strangeness distributions. We found that the results obtained from UrQMD calculations are comparable with the results from lattice QCD at low temperature and hadron resonance gas model. The ratios of mixed cumulants ($R_{11}^{BS},R_{13}^{BS},R_{22}^{BS},R_{31}^{BS}$) from UrQMD calculations show weak centrality dependence. However, the mixed-cumulant ratios $R_{11}^{BS}$ and $R_{31}^{BS}$ show strong increase at low energy, while the $R_{13}^{BS}$ and $R_{22}^{BS}$ are similar at different energies. Furthermore, we have also studied the correlations between different hadron species and their contributions to the net-baryon and net-strangeness correlations. These model studies can provide baselines for searching for the signals of QCD phase transition and critical point in heavy-ion collisions.

Figure 1

Baryon-strangeness (top) and electric charge-strangeness correlation (bottom), properly scaled by the strangeness fluctuations and the power of the fractional baryonic and electric charges [see Eq. (12)]. The figure is from Ref. [21].

Figure 2

(Top) The baryon-strangeness correlations for cases (iv)–(x) in the most central (0%–5%) $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathit{NN}}}=39\mathrm{GeV}$ from the UrQMD model. (Bottom) The centrality dependence of various order mixed cumulants ($C_{11}^{BS}, C_{13}^{BS}, C_{22}^{BS}, C_{31}^{BS}, C_{02}^{BS}, C_{04}^{BS}$) and ratios ($R_{11}^{BS}, R_{13}^{BS}, R_{22}^{BS}, R_{31}^{BS}$) of (iv)–(x) at $\sqrt{s_{\mathit{NN}}}=39\mathrm{GeV}$ for $\mathrm{Au}+\mathrm{Au}$ collisions from the UrQMD model.

Figure 3

(Left) The correlation between net baryon and net strangeness of (i)–(iv) at $\sqrt{s_{\mathit{NN}}}=39\mathrm{GeV}$ for the most central (0%–5%) $\mathrm{Au}+\mathrm{Au}$ collision from the UrQMD model. (Right) The centrality dependence of mixed cumulants ($C_{11}^{BS}, C_{13}^{BS}, C_{22}^{BS}, C_{31}^{BS}, C_{02}^{BS}, C_{04}^{BS}$) and ratios ($R_{11}^{BS}, R_{13}^{BS}, R_{22}^{BS}, R_{31}^{BS}$) for (i)–(iv) at $\sqrt{s_{\mathit{NN}}}=39\mathrm{GeV}$ for $\mathrm{Au}+\mathrm{Au}$ collisions from the UrQMD model.

Figure 4

The energy dependence of mixed cumulants and ratios of cases (i)–(iv) for the most central (0%–5%) $\mathrm{Au}+\mathrm{Au}$ collisions from the UrQMD model.

Figure 5

The energy dependence of various order mixed cumulants ($C_{11}^{BS}, C_{13}^{BS}, C_{22}^{BS}, C_{31}^{BS}, C_{02}^{BS}, C_{04}^{BS}$) and ratios ($R_{11}^{BS}, R_{13}^{BS}, R_{22}^{BS}, R_{31}^{BS}$) of cases (iv)–(x) at $\sqrt{s_{\mathit{NN}}}=7.7$, 11.5, 19.6, 27, 39, 62.4, and 200 GeV for the most central (0%–5%) $\mathrm{Au}+\mathrm{Au}$ collision from the UrQMD model.