Chaotic sources and Percolation of strings
  It is shown that different ways of interacting strings formed in high energy nucleus-nucleus collisions cause a different strength of the chaoticity parameter lambda of Bose-Einstein correlations. In particular, in the case of percolation of strings, lambda shows a peculiar dependence on the string density, very similar to the dependence of the fractional average cluster size. In both, the derivative on the string density is maximum at the critical point. The reasonable agreement with the existing experimental data indicates that percolation of strings can actually occurs. 
M. A. Braun, F. del Moral and C. Pajares