Measuring charge fluctuations in high-energy nuclear collisions

Various measures of charge fluctuations in heavy-ion collisions are discussed. Advantages of the $\Phi$ measure are demonstrated and its relation to other fluctuation measures is established. To get the relation, $\Phi$ is expressed through the moments of multiplicity distribution. We study how the measures act in the case of a “background” model that represents the classical hadron gas in equilibrium. The model assumes statistical particle production constrained by charge conservation. It also takes into account both the effect of incomplete experimental apparatus acceptance and that of tracking inefficiency. The model is shown to approximately agree with the PHENIX and preliminary STAR data on the electric charge fluctuations. Finally, “background-free” measures are discussed.