Incident energy dependence of $p_t$ correlations at relativistic energies

We present results for two-particle transverse momentum correlations, $\langle \Delta p_{t,i}\Delta p_{t,j}\rangle$, as a function of event centrality for Au+Au collisions at $\sqrt{s_{\mathit{NN}}}=20$, 62, 130, and 200 GeV at the BNL Relativistic Heavy Ion Collider. We observe correlations decreasing with centrality that are similar at all four incident energies. The correlations multiplied by the multiplicity density increase with incident energy, and the centrality dependence may show evidence of processes such as thermalization, jet production, or the saturation of transverse flow. The square root of the correlations divided by the event-wise average transverse momentum per event shows little or no beam energy dependence and generally agrees with previous measurements made at the CERN Super Proton Synchrotron.

Figure 1

(Color online) Histograms of the average transverse momentum per event for Au+Au at $\sqrt{s_{\mathit{NN}}}=20$, 62, 130, and 200 GeV for the 5% most central collisions at each energy. Both data and mixed events are shown for each incident energy. The lines represent gamma distributions.

Figure 2

(Color online) $\langle \Delta p_{t,i}\Delta p_{t,j}\rangle$ as a function of centrality and incident energy for Au+Au collisions compared with HIJING results.

Figure 3

(Color online) $(\mathit{dN}/d\eta )\langle \Delta p_{t,i}\Delta p_{t,j}\rangle$ as a function of centrality and incident energy for Au+Au collisions compared with HIJING results.

Figure 4

(Color online) $\sqrt{\langle \Delta p_{t,i}\Delta p_{t,j}\rangle }/\langle \langle p_t\rangle \rangle$ as a function of centrality and incident energy for Au+Au collisions compared with HIJING results for corresponding systems. The inset shows the excitation function for the most central bin.