The critical point in QCD and pion fluctuations in heavy ion collisions

A critical point of second order, belonging to the universality class of 3d Ising model, has been recently advocated as a strong candidate for the critical behaviour of QCD with non-zero quark masses. The implications of this conjecture are investigated, in the multiparticle environment of relativistic heavy ion collisions. A universal intermittency pattern of pion density fluctuations in momentum space is found reflecting the fractal structure of the critical system in configuration space. The association of this pattern with the critical exponents of the theory is discussed and the mechanism of generation of critical clusters is investigated. A Monte-Carlo simulation of critical events, in heavy ion collisions, reveals the detailed structure of these fluctuations, suggesting a framework of measurements (event-by-event) in which the critical theory of QCD may become falsifiable.