Event-by-event fluctuations of the charged particle ratio from nonequilibrium transport theory

The event-by-event fluctuations of the ratio of positively to negatively charged hadrons are predicted within the UrQMD model. Corrections for finite acceptance and finite net charge are derived. These corrections are relevant to compare experimental data and transport model results to previous predictions. The calculated fluctuations at RHIC and SPS energies are shown to be compatible with a hadron gas, thus, deviating by a factor of 3 from the predictions for a thermalized quark-gluon plasma.