High Energy and Nuclear Physics

Computational nuclear theory is providing the conceptual background to current and future experiments at DOE Office of High Energy and Nuclear Physics facilities. Current studies include the structure of atomic nuclei far from the stability line, and the dynamics of muon-induced nuclear fission, including the viscosity of nuclear matter. In simulations of relativistic heavy-ion collisions in a (3+1) dimensional classical string model, researchers have for the first time added structure functions for the nucleons, as well as mass quantization.

An increasing number of experimental physics applications, from heavy-ion fusion to high-energy colliders, demand higher-intensity beams, which places those beams in the space-charge dominated regime. Computational transport studies of space-charge dominated beams offer a low-cost approach for understanding their complicated physics. The simulations agree very well with the latest experimental observations and even reproduce the transverse density waves seen in experiments.

Nonequilibrium field theory covers a variety of topics such as transport theory of quantum fields, nonequilibrium phase transitions, the nucleation and transport of topological defects and other nonlinear coherent structures, as well as fundamental issues such as the quantum-classical transition and the coherent control of quantum systems. Computational physicists have recently shown that very high resolution simulations enable new methods for studying the statistical mechanics of field theories. These researchers have demonstrated how the classical limit of certain chaotic systems is obtained from quantum dynamics via decoherence, and have developed a new, accurate method for the characterization of classically chaotic systems.

Astrophysicists are developing new methods for analyzing data from cosmic microwave background detectors--the faintest echo of the Big Bang. Computing the maximum likelihood of signal to noise is the critical step in extracting useful information from the data. When all the radiation from astronomical objects is subtracted from what was detected, the cosmic microwave background is what is left over. Tiny perturbations in the background are an imprint of the primordial density fluctuations that seeded the formation of everything from planets to clusters of galaxies. Results of this research will help test the validity of competing cosmological models. Some models see non-topological semilocal strings as a possible source of the primordial density fluctuations. The first three-dimensional simulations of semilocal strings confirmed the possibility of their formation only 10^-35 of a second after the Big Bang.

NERSC's support of high energy and nuclear physics research is discussed below.

Simulated snapshots of electron density during a relativistic atomic collision provide information that cannot be accessed in a laboratory.