Forward-backward correlations in nucleus-nucleus collisions: Baseline contributions from geometrical fluctuations

Abstract

We discuss the effects of initial collision geometry and centrality bin definition on correlation and fluctuation observables in nucleus-nucleus collisions. We focus on the forward-backward correlation coefficient recently measured by the STAR Collaboration in $\mathrm{Au}+\mathrm{Au}$ collisions at RHIC. Our study is carried out within two models: the Glauber Monte Carlo code with a ``toy'' wounded-nucleon model and the hadron-string dynamics (HSD) transport approach. We show that strong correlations can arise from averaging over events in one centrality bin. We, furthermore, argue that a study of the dependence of correlations on the centrality bin definition as well as the bin size may distinguish between these trivial correlations and correlations arising from new physics.