Forward-backward multiplicity correlations in $\sqrt{s_{\mathit{NN}}}=200$ GeV Au+Au collisions

Forward-backward correlations of charged-particle multiplicities in symmetric bins in pseudorapidity are studied to gain insight into the underlying correlation structure of particle production in Au+Au collisions. The PHOBOS detector is used to measure integrated multiplicities in bins centered at η, defined within $\left|\eta \right|<3$, and covering intervals $\Delta \eta$. The variance ${\sigma }_C^2$ of a suitably defined forward-backward asymmetry variable $C$ is calculated as a function of $\eta ,\Delta \eta$, and centrality. It is found to be sensitive to short-range correlations, and the concept of “clustering” is used to interpret comparisons to phenomenological models.

Figure 1

Number of hits vs total deposited energy (in keV) measured $-0.5<\eta <0$ (in the Octagon detector) for 200 GeV Au+Au collisions. Solid line is a function, described in the text, fit to the mean number of hits in each energy bin.

Figure 2

Contributions to ${\sigma }_C^2$ from sources other than primary charged particles.

Figure 3

Example of the analysis method, showing values for ${\sigma }_{C,\mathrm{raw}}^2,{\sigma }_{\det }^2$ and the final ${\sigma }_C^2$, as a function of η for $\Delta -\eta =0.5$. These values are calculated for the half-azimuth ($\Delta \varphi =\pi$) acceptance, which is corrected for in the final result.

Figure 4

Calibration of reconstruction method with MC simulations, as a function of η with $\Delta \eta =0.5$. Solid points represent MC truth information on ${\sigma }_C^2$; open symbols, outcome of reconstruction.

Figure 5

Upper: ${\sigma }_C^2$ for a fixed $\Delta \eta =0.5$ as a function of η. Lower: ${\sigma }_C^2$ as a function of $\Delta \eta$ for a fixed bin center at $\eta =2.0$. Statistical errors are vertical bars; systematic errors are brackets.