Energy and system-size dependence of two- and four-particle $v_2$ measurements in heavy-ion collisions at RHIC and their implications on flow fluctuations and nonflow

The collaboration
Phys.Rev.C 86 (2012) 014904, 2012.

Abstract
We present STAR measurements of azimuthal anisotropy by means of the two- and four-particle cumulants $v_2$ ($v_2\{2\}$ and $v_2\{4\}$) for Au+Au and Cu+Cu collisions at center of mass energies $\sqrt{s_{_{\mathrm{NN}}}} = 62.4$ and 200 GeV. The difference between $v_2\{2\}^2$ and $v_2\{4\}^2$ is related to $v_{2}$ fluctuations ($\sigma_{v_2}$) and nonflow $(\delta_{2})$. We present an upper limit to $\sigma_{v_2}/v_{2}$. Following the assumption that eccentricity fluctuations $\sigma_{\epsilon}$ dominate $v_2$ fluctuations $\frac{\sigma_{v_2}}{v_2} \approx \frac{\sigma_{\epsilon}}{\epsilon}$ we deduce the nonflow implied for several models of eccentricity fluctuations that would be required for consistency with $v_2\{2\}$ and $v_2\{4\}$. We also present results on the ratio of $v_2$ to eccentricity.

• #### Figure 1 (left)

Data from Figure 1, left pannel

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The two-particle cumulant $v_2\{2\}^2$ for Au+Au collisions at 200 and 62.4 GeV. Results are shown with like-sign combinations (LS) and...

• #### Figure 1 (right)

Data from Figure 1, right pannel

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The same as the left but for Cu+Cu collisions. The systematic errors are shown as thin lines with wide caps...

• #### Figure 2 (up)

Data from Figure 2, upper pannel

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The difference of charge-independent (CI) v2{2} and like-sign (LS) $v_2\{2\}$ for Au+Au and Cu+Cu collisions at 200 (top panel) and...

• #### Figure 2 (bottom)

Data from Figure 2, bottom pannel

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The difference of charge-independent (CI) v2{2} and like-sign (LS) $v_2\{2\}$ for Au+Au and Cu+Cu collisions at 200 (top panel) and...

• #### Figure 3 (left)

Data from Figure 3, left pannel

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• #### Figure 4

Data from Figure 4

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The difference of charge-independent (CI) $v_2\{4\}$ and like-sign (LS) $v_2\{4\}$ for Au+Au collisions at 200 and 62.4 GeV vs. the...

• #### Figure 5 (left)

Data from Figure 5, left pannel

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(Left) The difference between $v_2\{2\}^2$ and $v_2\{4\}^2$ for 200 GeV Au+Au and Cu+Cu collisions for both LS and CI combinations.

• #### Figure 5 (right)

Data from Figure 5, right pannel

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(Right) The difference between $v_2\{2\}^2$ and $v_2\{4\}^2$ for 62.4 GeV Au+Au and Cu+Cu collisions for both LS and CI combinations....

• #### Figure 6 (left)

Data from Figure 6, left pannel

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The upper limit on $\sigma_{v_2}/\langle v_2 \rangle$ for 200 GeV (left) and 62.4 GeV (right) Au+Au collisions from Eq. (9)...

• #### Figure 6 (right)

Data from Figure 6, right pannel

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The upper limit on $\sigma_{v_2}/\langle v_2 \rangle$ for 200 GeV (left) and 62.4 GeV (right) Au+Au collisions from Eq. (9)...

• #### Figure 7

Data from Figure 7

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The STAR data compared to PHOBOS data [34] on $\sigma_{v_2}/\langle v_2 \rangle$ with $\delta_2$ for $\Delta\eta > 2$ taken to...

• #### Figure 8 (left)

Data from Figure 8, left pannel

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The upper limit on $\sigma_{v_2}/\langle v_2 \rangle$ for 200 GeV (left) and 62.4 GeV (right) Cu+Cu collisions from Eq. (9)...

• #### Figure 8 (right)

Data from Figure 8, right pannel

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The upper limit on $\sigma_{v_2}/\langle v_2 \rangle$ for 200 GeV (left) and 62.4 GeV (right) Cu+Cu collisions from Eq. (9)...

Version 2 modifications: Correct an accidental swapping of systematic and statistical uncertainties. This affects Figs. 3 and 5