Enhanced strange baryon production in Au+Au collisions compared to $p+p$ at $\sqrt{s_{\mathit{NN}}}=200$ GeV

We report on the observed differences in production rates of strange and multistrange baryons in Au+Au collisions at $\sqrt{s_{\mathit{NN}}}=200$ GeV compared to $p+p$ interactions at the same energy. The strange baryon yields in Au+Au collisions, when scaled down by the number of participating nucleons, are enhanced relative to those measured in $p+p$ reactions. The enhancement observed increases with the strangeness content of the baryon, and it increases for all strange baryons with collision centrality. The enhancement is qualitatively similar to that observed at the lower collision energy $\sqrt{s_{\mathit{NN}}}=17.3$ GeV. The previous observations are for the bulk production, while at intermediate $p_T,1<p_T<4$ GeV/$c$, the strange baryons even exceed binary scaling from $p+p$ yields.

Figure 1

Midrapidity $E(i)$ as a function of $\langle N_{\mathrm{part}}\rangle$ for $\Lambda ,\overline{\Lambda }$ ($\left|y\right|<1.0$), ${\Xi }^{-},{\overline{\Xi }}^{+},{\Omega }^{-}+{\overline{\Omega }}^{+}$ ($\left|y\right|<0.75$), and inclusive $p$ ($\left|y\right|<0.5$). Boxes at unity show statistical and systematic uncertainties combined in the $p+p$ ($p+\mathrm{Be}$) data. Error bars on the data points represent those from the heavy ions. The solid markers are for Au+Au at $\sqrt{s_{\mathit{NN}}}=200$ GeV and the open symbols for Pb+Pb ($\left|y\right|<0.5$) at $\sqrt{s_{\mathit{NN}}}=17.3$ GeV [4]. The arrows on the right axes mark the predictions from a GC formalism model when varying $T$ from 165 MeV [$E({\Xi }^{-})=10.7,E(\Lambda )=2.6$] to 170 MeV [$E({\Xi }^{-})=7.5,E(\Lambda )=2.2$]. The red arrows indicate the predictions for Ξ and the black arrows those for Λ, see text for details [12].

Figure 2

$R_{\mathrm{AA}}$ from (a) $0\text{−}5\%$ and (b) $60\text{−}80\%$ central Au+Au events for $p+\overline{p}$ [18, 19], $\Lambda ,$ and ${\Xi }^{-}+{\overline{\Xi }}^{+}$. Errors shown are statistical plus systematic added in quadrature. The band at unity shows the systematic uncertainty on $\langle N_{\mathrm{bin}}\rangle$. The dashed line below unity shows the expected value of $R_{\mathrm{AA}}$ should the yields scale with $\langle N_{\mathrm{part}}\rangle$, and the band around it shows the systematic uncertainty on $\langle N_{\mathrm{part}}\rangle$.

Figure 3

$R_{\mathrm{CP}}$ Au+Au events for $p+\overline{p}(0\text{−}12\%/60\text{−}80\%)$ [19], and $\Lambda +\overline{\Lambda }$ and ${\Xi }^{-}+{\overline{\Xi }}^{+}(0\text{−}5\%/60\text{−}80\%)$ [5]. Also shown as the dashed curve are the results for $4h^{+}+h^{-}$ for $0\text{−}5\%/60\text{−}80\%$ [20]. Errors shown are statistical plus systematic added in quadrature. The band at unity shows the systematic uncertainty on $\langle N_{\mathrm{bin}}\rangle$. The dashed line below unity shows the expected value of $R_{\mathrm{CP}}$ should the yields scale with $\langle N_{\mathrm{part}}\rangle$, and the band around it shows the systematic uncertainty on $\langle N_{\mathrm{part}}\rangle$.

Figure 4

Comparison of $R_{\mathrm{AA}}$ from data to HIJING [26] and EPOS [29] for $0\text{−}5\%$ and $60\text{−}80\%$ most central Au+Au collisions, for $p+\overline{p},\Lambda$, and ${\Xi }^{-}+{\overline{\Xi }}^{+}$. Errors shown are statistical plus systematic added in quadrature. The bands at unity shows the systematical uncertainty on $\langle N_{\mathrm{bin}}\rangle$. The bands below unity on the left of the graphs are centered at the expected value of $R_{\mathrm{AA}}$ should the yields scale with $\langle N_{\mathrm{part}}\rangle$, and the widths of the bands indicate the systematic uncertainty on $\langle N_{\mathrm{part}}\rangle$.