System size and centrality dependence of the balance function in $A+A$ collisions at $\sqrt{s_{\mathrm{NN}}}=17.2$ GeV

Electric charge correlations were studied for p+p, C+C, Si+Si, and centrality selected Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}}=17.2$ GeV with the NA49 large acceptance detector at the CERN SPS. In particular, long-range pseudorapidity correlations of oppositely charged particles were measured using the balance function method. The width of the balance function decreases with increasing system size and centrality of the reactions. This decrease could be related to an increasing delay of hadronization in central Pb+Pb collisions.

Figure 1

(Color online) the experimental setup of the NA49 experiment with different beam definitions and target arrangements.

Figure 2

(Color online) the acceptance curves in the $p_T-<$ plane for $2.5<y<2.7$ (left plot) and $4.1<y<4.3$ (right plot) at $\sqrt{s_{\mathrm{NN}}}=17.2$ GeV.

Figure 3

The pseudorapidity distribution of the accepted charged particles in central Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}}=17.2$ GeV.

Figure 4

(Color online) the BF versus $\Delta \eta$ for different centrality classes of Pb+Pb collisions for real data as well as for shuffled, mixed, and HIJING events. The curves show Gaussian fits.

Figure 5

(Color online) the BF versus $\Delta \eta$ for real, shuffled, and $\text{HIJING}$ events (together with the Gaussian fits) for Si+Si (upper panel), C+C (middle panel), and p+p (lower panel) collisions.

Figure 6

(Color online) the width of the BF as a function of the event selection cut $\Delta z$ (upper panel) and the track selection cuts $\left|d_x\right|{}_{\max }$ (middle panel), and the $\left|d_y\right|{}_{\max }$ (lower panel) for p+p, Pb+Pb peripheral, and Pb+Pb central data.

Figure 7

(Color online) the BF versus $\Delta \eta$ for three centrality classes of Pb+Pb collisions together with the Gaussian fits. The distributions were normalized to the same integral for this comparison.

Figure 8

(Color online) the dependence of the BF's width on the number of wounded nucleons for p+p, C+C, Si+Si, and Pb+Pb collisions.

Figure 9

(Color online) the dependence of the BF's width on the normalized impact parameter $〈b〉/b_{\max }$ for Pb+Pb collisions.

Figure 10

(Color online) the dependence of the BF's width on the normalized impact parameter $〈b〉/b_{\max }$, as measured by NA49 for Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}}=17.2$ GeV and by STAR for Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}=130$ GeV.