Energy correlations as thermodynamical signals for phase transitions in finite systems

A new method is proposed to extract information on the properties of the possible phase transition occurring in finite systems as multifragmenting atomic nuclei. The average energy of a subsystem is demonstrated to provide a thermometer when data are sorted in total excitation energy bins, while the associated fluctuations are quantitatively related to the heat capacity. A coupled analysis with total energy fluctuations in bins of the partial energy allows us to detect the presence of a phase transition and the associated order. Deformations due to finite size effects and experimental cuts are also discussed.