Experimental Signals of the First Phase Transition of Nuclear Matter

Vaporized and multifragmenting sources produced in heavy ion collisions at intermediate energies are good candidates to investigate the phase diagram of nuclear matter. The properties of highly excited nuclear sources which undergo a simultaneous disassembly into particles are found to sign the presence of a gas phase. For heavy nuclear sources produced in the Fermi energy domain, which undergo a simultaneous disassembly into particles and fragments, a fossil signal (fragment size correlations) reveals the origin of multifragmentation:spinodal instabilities which develop in the unstable coexistence region of the phase diagram of nuclear matter. Studies of fluctuations give a direct signature of a first order phase transition through measurements of a negative microcanonical heat capacity.