Long-range charge fluctuations and search for a quark-gluon plasma signal

We critically discuss a recent suggestion to use long-range modes of charge (electric or baryon) fluctuations as a signal for the presence of quark-gluon plasma at the early stages of a heavy ion collision. We evaluate the rate of diffusion in rapidity for different secondaries, and argue that for conditions of the Super Proton Synchrotron (SPS) experiments, it is strong enough to relax the magnitude of those fluctuations almost to its equilibrium values, given by hadronic "resonance gas." We evaluate the detector acceptance needed to measure such "primordial'' long-range fluctuations at Relativistic Heavy Ion Collider (RHIC) conditions. We conclude with an application of the charge fluctuation analysis to the search for the QCD critical point.