System-size dependence of transverse momentum correlations at $\sqrt{s_{NN}}=62.4$ and 200 GeV at the BNL Relativistic Heavy Ion Collider

We present a study of the average transverse momentum ($p_t$) fluctuations and $p_t$ correlations for charged particles produced in Cu+Cu collisions at midrapidity for $\sqrt{s_{NN}}=$ 62.4 and 200 GeV. These results are compared with those published for Au+Au collisions at the same energies, to explore the system size dependence. In addition to the collision energy and system size dependence, the $p_t$ correlation results have been studied as functions of the collision centralities, the ranges in $p_t$, the pseudorapidity $\eta$, and the azimuthal angle $\varphi$. The square root of the measured $p_t$ correlations when scaled by mean $p_t$ is found to be independent of both colliding beam energy and system size studied. Transport-based model calculations are found to have a better quantitative agreement with the measurements compared to models which incorporate only jetlike correlations.

Figure 1

Event-by-event $\langle p_t\rangle$ distributions for data and mixed events in central Cu+Cu collisions at (a) $\sqrt{s_{NN}}=$ 200 and (b) 62.4 GeV. The curves (solid for data and dotted for mixed events) represent the $\Gamma$ distributions. The errors shown are statistical.

Figure 2

Comparison of dynamical $\langle p_t\rangle$ fluctuations in Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}}=$ 62.4 and 200 GeV as a function of the number of participating nucleons.

Figure 3

(a) $p_t$ correlations, (b) $p_t$ correlations multiplied by $\langle N_{\mathrm{part}}\rangle /2$, (c) square root of $p_t$ correlations scaled by $\langle \langle p_t\rangle \rangle$, and (d) square root of $p_t$ correlations multiplied by $\langle N_{\mathrm{part}}\rangle /2$ and scaled by $\langle \langle p_t\rangle \rangle$, plotted vs $\langle N_{\mathrm{part}}\rangle$. Results are compared between Cu+Cu and Au+Au collisions at $\sqrt{s_{NN}}=$ 62.4 and 200 GeV. Au+Au data have been taken from Ref. [30].

Figure 4

Comparison of scaled $p_t$ correlations between data and models for Au+Au [panels (a) and (c)] and Cu+Cu [panels (b) and (d)[ collisions at 200 GeV. Au+Au data have been taken from Ref. [30]. The curves represent different model calculations.

Figure 5

$p_t$ correlations for varying rapidity acceptance ($\left|\eta \right|<$ 0.25, 0.5, and 1.0) for Cu+Cu collisions at $\sqrt{s_{NN}}=$ 200 GeV [panel (a)] and 62.4 GeV [panel (b)].

Figure 6

$p_t$ correlations for varying azimuthal acceptance for Cu+Cu collisions at $\sqrt{s_{NN}}=$ 200 GeV [panels (a) and (c)] and 62.4 GeV [panels (b) and (d)].

Figure 7

$p_t$ correlations plotted as a function of $\langle N_{\mathrm{part}}\rangle$ for different $p_t$ ranges in Cu+Cu collisions at (a) 200 GeV and (b) 62.4 GeV.

Figure 8

Correlations for varying $p_t$ ranges for different model calculations in Cu+Cu 200 GeV: (a) ampt (SM), (b) urqmd, and (c) hijing (no JQ).

Figure 9

Top panel: Uncorrected inclusive charged particle $p_t$ spectrum for 0$\%$–10$\%$ collision centrality for Cu+Cu 200 GeV (open circles). The distribution is a fit to the exponential function $A{e}^{-p_t/T}$ (red dashed line). Errors are statistical. Bottom panel: Correlations scaled by ${(d\langle p_t\rangle /dT)}^2{T}^2$ vs $\langle N_{\mathrm{part}}\rangle$ for different $p_t$ ranges in Cu+Cu 200 GeV.