Pion-Kaon Correlations in Central $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ Collisions at $\sqrt{s_{NN}}=130\mathrm{G}\mathrm{e}\mathrm{V}$

Pion-kaon correlation functions are constructed from central $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ STAR data taken at $\sqrt{s_{NN}}=130\mathrm{G}\mathrm{e}\mathrm{V}$ by the STAR detector at the Relativistic Heavy Ion Collider (RHIC). The results suggest that pions and kaons are not emitted at the same average space-time point. Space-momentum correlations, i.e., transverse flow, lead to a space-time emission asymmetry of pions and kaons that is consistent with the data. This result provides new independent evidence that the system created at RHIC undergoes a collective transverse expansion.

Figure 1

Top panels: pion-kaon correlation functions $C(k^{*})$, the average of $C_{+}(k^{*})$ and $C_{-}(k^{*})$. Middle and bottom panels: ratio of the correlation functions $C_{+}$ and $C_{-}$ defined with the sign of the projections, $k_{\mathrm{o}\mathrm{u}\mathrm{t}}^{*}$, $k_{\mathrm{s}\mathrm{i}\mathrm{d}\mathrm{e}}^{*}$, and $k_{\mathrm{l}\mathrm{o}\mathrm{n}\mathrm{g}}^{*}$. Errors are statistical only. The horizontal axis of the ratios $C_{+}/C_{-}$ for $k_{\mathrm{s}\mathrm{i}\mathrm{d}\mathrm{e}}^{*}$ ($k_{\mathrm{l}\mathrm{o}\mathrm{n}\mathrm{g}}^{*}$) is shifted by $1\mathrm{M}\mathrm{e}\mathrm{V}/c$ ($2\mathrm{M}\mathrm{e}\mathrm{V}/c$) to separate the error bars.

Figure 2

Comparison of the pion-kaon correlation functions obtained from data and model calculations. Upper panel: $C(k^{*})$. Lower panel: $C_{+}(k_{\mathrm{o}\mathrm{u}\mathrm{t}}^{*})/C_{-}(k_{\mathrm{o}\mathrm{u}\mathrm{t}}^{*})$. Model calculations are the lines above 1 for unlike-sign pairs and below 1 for like-sign pairs.