Electric charge fluctuations in central $\mathrm{Pb}+\mathrm{Pb}$ collisions at $20A,30A,40A,80A$, and $158A\mathrm{GeV}$

Results are presented on event-by-event electric charge fluctuations in central $\mathrm{Pb}+\mathrm{Pb}$ collisions at $20A,30A,40A,80A$, and $158A\mathrm{GeV}$. The observed fluctuations are close to those expected for a gas of pions correlated by global charge conservation only. These fluctuations are considerably larger than those calculated for an ideal gas of deconfined quarks and gluons. The present measurements do not necessarily exclude reduced fluctuations from a quark-gluon plasma because these might be masked by contributions from resonance decays.

Figure 1

The experimental setup of the NA49 experiment.

Figure 2

Distributions of registered particles in the $p_T-\varphi$ plane for $-0.2<y<0$ (a) and $1.4<y<1.6$ (b) at $20A\mathrm{GeV}$ and $-0.6<y<-0.4$ (c) and $1.4<y<1.6$ (d) at $158A\mathrm{GeV}$. The acceptance limits used in the analysis are shown by the solid lines.

Figure 3

The rapidity distribution of accepted particles in central $\mathrm{Pb}+\mathrm{Pb}$ collisions at $158A\mathrm{GeV}$. The largest rapidity interval used for the analysis is indicated by dashed lines.

Figure 4

The distribution of the net charge for central $\mathrm{Pb}+\mathrm{Pb}$ collisions at $158A\mathrm{GeV}$ (solid line) and the corresponding distribution obtained for mixed events (dotted line) in the maximum rapidity interval $\Delta y=3$.

Figure 5

The dependence of the measure ${\Phi }_q$ on the fraction of accepted particles for central $\mathrm{Pb}+\mathrm{Pb}$ collisions at $\left(20\text{−}158\right)A\mathrm{GeV}$. Note that experimental points for a given energy are correlated as the data used for a given rapidity interval are included in the broader intervals. The dashed line shows the dependence expected for the case when the only source of particle correlations is the global charge conservation, Eq. (3).

Figure 6

The dependence of $\Delta {\Phi }_q$ on the width of the rapidity interval $\Delta y$ for central $\mathrm{Pb}+\mathrm{Pb}$ collisions at $20A,30A,40A,80A$ and $158A\mathrm{GeV}$. Note that experimental points for a given energy are correlated as the data used for a given rapidity interval are included in the broader intervals.

Figure 7

The energy dependence of $\Delta {\Phi }_q$ measured in central $\mathrm{Pb}+\mathrm{Pb}$ collisions for a narrow rapidity interval $\Delta y=1.2$ (left) and a broad rapidity interval $\Delta y=3$ (right).

Figure 8

The dependence of $\Delta {\Phi }_q$ on the fraction of accepted particles in central $\mathrm{Pb}+\mathrm{Pb}$ collisions at $\left(20\text{−}158\right)A\mathrm{GeV}$. The prediction for the ideal QGP is indicated by the dashed curve (QGP), whereas the prediction for the QGP including hadronization and resonance decay is shown by the dotted curve $(\mathrm{QGP}+\text{hadronization})$.