Correlations and Fluctuations in High-Energy Collision

In addition to its importance in describing high-energy processes themselves, the dynamics of multiparticle production is part of the general field of non-linear phenomena and complex systems. Multiparticle dynamics is one of the rare fields of physics where higher-order correlations are directly accessible in their full multi-dimensional characteristics under well-controlled experimental conditions. Multiparticle dynamics, therefore, is an ideal testing ground for the development of advanced statistical methods. Higher-order correlations have, indeed, been observed as particle-density fluctuations. Approximate scaling with finer resolution provides evidence for a self-similar correlation effect. Quantum-Chromodynamics branching is a good candidate for a dynamical explanation of these correlations in e+e- collisions at CERN/LEP and, as expected, also of those in pp collisions at future CERN/LHC energies. However, other sources such as identical-particle Bose-Einstein interference effects also contribute. A particular question at the moment is the smooth transition from the QCD branching domain (gluon interference before hadronization) to the Bose-Einstein domain (identical-pion interference after hadronization). Both mechanisms have clearly been observed in e+e- collisions at CERN/LEP energies. The large amount of high-resolution data being collected at LEP will allow the study of the genuine (i.e. non-trivial) higher-order correlations in both domains.