Fluctuations and deconfinement phase transition in nucleus-nucleus collisions

We propose a method to experimentally study the equation of state of strongly interacting matter created at the early stage of nucleus-nucleus collisions. The method exploits the relation between relative entropy and energy fluctuations and equation of state. As a measurable quantity, the ratio of properly filtered multiplicity to energy fluctuations is proposed. Within a statistical approach to the early stage of nucleus-nucleus collisions, the fluctuation ratio manifests a non-monotonic collision energy dependence with a maximum in the domain where the onset of deconfinement occurs.