Source Chaoticity in Relativistic Heavy Ion Collisions at SPS and RHIC
We investigate degree of coherence of pion sources produced in relativistic heavy ion collisions using multi-particle interferometry. In order to obtain ''true'' chaoticity, ltrue from two-pion correlation functions measured in experiments, we make a correction for long-lived resonance decay contributions. Using this ltrue and the weight factor which are obtained from parameter fitted to two- and three-pion correlation function, we calculate a chaotic fraction e and the number of coherent sources a for different colliding energies. The result gives constraints on the source and shows an increase of the minimum number of a with multiplicity, although multiplicity independent chaoticity is not excluded.