Beam-energy and system-size dependence of dynamical net charge fluctuations

We present measurements of net charge fluctuations in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathit{NN}}}=19.6$, $62.4$, $130$, and $200$ GeV, $\mathrm{Cu}+\mathrm{Cu}$ collisions at $\sqrt{s_{\mathit{NN}}}=62.4$ and $200$ GeV, and $p+p$ collisions at $\sqrt{s}=200$ GeV using the dynamical net charge fluctuations measure ${\nu }_{+-,\mathrm{dyn}}$. We observe that the dynamical fluctuations are nonzero at all energies and exhibit a modest dependence on beam energy. A weak system size dependence is also observed. We examine the collision centrality dependence of the net charge fluctuations and find that dynamical net charge fluctuations violate $1/N_{\mathrm{ch}}$ scaling but display approximate $1/N_{\mathrm{part}}$ scaling. We also study the azimuthal and rapidity dependence of the net charge correlation strength and observe strong dependence on the azimuthal angular range and pseudorapidity widths integrated to measure the correlation.

Figure 1

Dynamical net charge fluctuations, ${\nu }_{+-,\mathrm{dyn}}$, of particles produced within pseudorapidity $\left|\eta \right|<0.5$, as function of the number of participating nucleons.

Figure 2

Corrected values of dynamical net charge fluctuations (${\nu }_{+-,\mathrm{dyn}}^{\mathrm{corr}}$) measured in central collisions as a function of $\sqrt{s_{\mathit{NN}}}$. See text for details.

Figure 3

Dynamical net charge fluctuations ${\nu }_{+-,\mathrm{dyn}}$ of particles produced with pseudorapidity $\left|\eta \right|<0.5$ scaled by (a) the multiplicity ${\mathit{dN}}_{\mathrm{ch}}/d\eta$, where the dashed line corresponds to charge conservation effect and the solid line to the prediction for a resonance gas, (b) the number of participants, and (c) the number of binary collisions.

Figure 4

Dynamical fluctuations ${\nu }_{+-,\mathrm{dyn}}$, normalized to their value for $\left|\eta \right|<1$, as function of the integrated pseudorapidity range. (a) Data for $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathit{NN}}}=62.4,200$ GeV (0–5%) and for $\mathrm{Cu}+\mathrm{Cu}$ collisions at $\sqrt{s_{\mathit{NN}}}=62.4,200$ GeV (0–10%) are compared with inclusive $p+p$ data at $\sqrt{s}=200$ GeV. (b) Data for $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathit{NN}}}=62.4,200$ GeV (30–40%) and for $\mathrm{Cu}+\mathrm{Cu}$ collisions at $\sqrt{s_{\mathit{NN}}}=62.4,200$ GeV (0–10%) are compared with inclusive $p+p$ collision data at $\sqrt{s}=200$ GeV.

Figure 5

Dynamical fluctuations ${\nu }_{+-,\mathrm{dyn}}$ as a function of the integrated azimuthal range ϕ for selected collision centralities for (a) $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathit{NN}}}=200$ GeV and (b) $\mathrm{Cu}+\mathrm{Cu}$ collisions at $\sqrt{s_{\mathit{NN}}}=200$ GeV.

Figure 6

Dynamical fluctuations ${\nu }_{+-,\mathrm{dyn}}$ as a function of the integrated azimuthal range ϕ for similar number of participating nucleons for $\mathrm{Au}+\mathrm{Au}$ and $\mathrm{Cu}+\mathrm{Cu}$ collisions at $\sqrt{s_{\mathit{NN}}}=200$ GeV.