Anomalous multiplicity fluctuations from phase transitions in heavy-ion collisions

Event-by-event fluctuations and correlations between particles produced in relativistic nuclear collisions are studied. The fluctuations in positive, negative, total, and net charge are closely related through correlations. In the event of a phase transition to a quark-gluon plasma, fluctuations in total and net charge can be enhanced and reduced, respectively, which, however, is very sensitive to the acceptance and centrality. If the colliding system experiences strong density fluctuations due, e.g., to droplet formation in a first-order phase transition. all fluctuations can be enhanced substantially. The importance of fluctuations and correlations is exemplified by event-by-event measurement of the multiplicities of J/Psi 's and charged particles since these observables should anticorrelate in the presence of comover or anomalous absorption.