Boltzmann-Langevin Transport Model for Heavy-Ion Collisions

Abstract

Many aspects of heavy-ion collisions can be described by means of the one-body transport models. In these transport models, one deals with a reduced description in terms of the single-particle density, rather than the full many-body information. These models in semi-classical limit with a Boltzmann-Uehling-Uhlenbeck (BUU) form of a collision term has been very successful in describing a large variety of observables associated with heavy-ion collisions at intermediate energies^1–2. The average description provided by the BUU model is well suited for processes involving small density fluctuations. However, for processes involving large density fluctuations, for example near instabilities and bifurcations, such an average description is inadequate. In these situations the stochastic transport models may provide a more appropriate basis for describing the dynamical evolution. In these stochastic approaches, the one-body transport models are improved beyond the mean-field approximation by incorporating the high order correlations in a statistical approximation, analogous to the treatment of the Brownian motion. The recently developed Boltzmann-Langevin (BL) model constitutes an example of such stochastic transport approaches,^3–5 and it is therefore a promising model for describing catastrophic phenomena, such as phase transitions and nuclear multifragmentations.