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Predicting the Subatomic Future

Photo of Martin Savage

Martin Savage, UW Professor of Physics

Martin Savage, Professor of Physics at the UW, is one Principal Investigator (PI) of a team associated with a National Science Foundation grant of $750,000 for Major Research Instrumentation (MRI).  The instrument in this case is the team’s set of 140 Hyak nodes, 140TB of fast shared storage, and associated equipment that they use to develop next-generation computational techniques for nuclear and particle physics. Hyak, a shared high performance computer cluster dedicated to research computing at UW, is indispensable as the team prepares to run at petascale and exascale computing within the decade.

Hyak’s considerable capability supports the development of techniques required for precision calculations of nuclear reaction rates. Ultimately, the goal is to simulate nuclear reactions better than we can now. The numerical solution of quantum chromodynamics, the theory underlying the strong force, has potential impact in multiple areas, and, eventually, it is hoped that it will be used to refine larger scale nuclear calculations used to deal with complex nuclear systems, for instance, in the design of nuclear reactors.

“You want to get to the stage where you can calculate reliably anything of importance in nuclear systems and in nuclear astrophysics. You want to develop a computational tool that will give you results with quantifiable uncertainties that can be systematically eliminated,” Savage said.

Strong Forces, Quarks, Gluons

Savage’s work explores the strong nuclear force among quarks and gluons, the subatomic particles that form atomic nuclei. The strong force between quarks is the most powerful force in nature, binding quarks and gluons together to form protons, neutrons, pions, and more exotic particles. It also gives rise to a force between the neutrons and protons that overpowers the electromagnetic repulsion between protons to bind the atomic nucleus together. The long-range nature of the electromagnetic force (combined with the Pauli-exclusion principle, an entirely quantum phenomenon) eventually overcomes the short-range nature of the strong force to destabilize very large nuclei. (This underlies the process of fission and explains why super heavy elements have not been observed.)

Atoms to Quarks

An atom is composed of a dense nucleus at its center surrounded by a diffuse cloud of electrons. The nucleus is comprised of neutrons and protons that interact with each other via the short-distance strong force. Further, the protons also interact with themselves via the long-distance Coulomb force (electromagnetic). The neutrons and protons are composite objects formed from quarks and gluons, whose dynamics are governed by the underlying theory called quantum chromodynamics.

 

Unlike some other fields of research, where large data sets have yet to be explored to uncover empirical rules that describe the data, the underlying laws that determine nuclear physics were established and verified during the last century with substantial experimental and theoretical investigations. However, knowing the laws that govern the strong forces between quarks and gluons, and using them to make precise predictions for nuclear processes, are two different things.

Today, researchers can use their knowledge of the laws to create well-defined calculations with the goal of predicting nuclear reaction rates to precision. “We can’t get at some important reactions or structures experimentally [or analytically],” Savage said.