Like every branch of the physical sciences, the backbone of nuclear science is theory. Every experiment, calculation, result and prediction starts and ends with nuclear theory.
Nuclear theory has many facets. How do protons and neutrons interact to produce matter as we know it? What are the limits of stability? How do neutrons and protons organize themselves to produce regular patterns and shapes? This branch is usually referred to as nuclear structure. To answer these questions we need to understand the force and how it emerges from the fundamental theory of Quantum Chromodynamics.
Theory is also essential for understanding how nuclei interact during a reaction experiment and making sense of the results. This branch is called reaction theory. Being able to detect particles and the products of a nuclear reaction is only valuable if the nuclear theory is adequate and can reconstruct what happened.
Theory and experiment go hand in hand. Theory makes predictions and motivate experiments. Experimental results are used to update, improve and validate the framework that nuclear scientists work within. The models are reassessed under the light of the new data. The new information then comes full circle by helping to determine which experiments are conducted next. By knowing where the gaps in knowledge are – where nuclear theory needs more information – scientists can better decide which questions to ask and which experiments to run next.
Although most nuclear theorists at NSCL connect to the science of rare isotopes, a few are more interested in high-energy phenomena, when quark degrees of freedom become important. This includes understanding high-density matter and developing theory relevant to experiments at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). These are just a few of the examples of what theorists are up to at NSCL.