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

TL;DR

This paper investigates how initial collision geometry and centrality definitions influence forward-backward correlations in nucleus-nucleus collisions, highlighting the importance of baseline effects from geometrical fluctuations.

Contribution

It compares two models to analyze the impact of geometrical fluctuations on correlation measurements, providing a baseline for distinguishing trivial from new physics effects.

Findings

Strong correlations can result from event averaging within a centrality bin.

Dependence of correlations on bin size can help identify non-trivial physics.

Baseline effects from geometrical fluctuations are significant in correlation analyses.

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 Au+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 due to 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'.