Overview

The purpose of the program is to bring together physicists from the low-energy nuclear structure and reaction communities to identify avenues for achieving reliable and predictive descriptions of reactions involving nuclei across the isotopic chart.

Recent years have seen exciting new developments and progress in nuclear reaction theory that allow us to move towards a description of exotic systems and environments, providing deeper insights into the dynamics of the nuclear many-body system, and setting the stage for new discoveries. For very light nuclei, remarkable progress has been made with ab initio theories, which describe the systems from first principles, using realistic interactions. At the same time, an intense interest in heavier nuclei, aided by the availability of dramatically increased computing power, has driven new developments in shell-model approaches and density-functional theories. These structure approaches provide crucial input for reaction descriptions.

Experimental facilities involving radioactive ion beams and dramatically-improved multi-physics simulation capabilities provide new challenges and opportunities. Nuclear theory must address phenomena from laboratory experiments to stellar environments, from stable nuclei to weakly-bound and exotic isotopes. Expanding the reach of theory to these regimes requires a comprehensive understanding of the reaction mechanisms involved as well as detailed knowledge of nuclear structure. A collective effort of the reaction and structure community is essential to address major open questions about the nature of strongly interacting matter and the origin of the elements.

Goals

The program aims to intensify the dialogue and to work towards a better integration of the complementary theory efforts. The embedded workshop specifically intends to integrate experimental research as well as to take into account needs of the nuclear data community. We will focus on two essential goals:

• Determine strategies for expanding current ab initio nuclear structure and reaction descriptions towards medium-mass nuclei;

• Determine strategies for moving towards microscopic theories of heavy nuclei to achieve increasingly more predictive descriptions of the structure and reactions of heavy nuclei.

• Integrated structure and reaction ab initio modeling: Addressing the challenge of heavier nuclei, continuum, and multiple reaction channels.
  Ab initio approaches carry predictive power, which is critical for studying short-lived isotopes inaccessible by experiment, but are currently limited to light nuclei. Following the development of ab initio structure models that exhibit a better scaling, the program will discuss and guide the development of ab initio reaction theory for medium-mass nuclei.

• Effective interactions in reaction calculations.
  Effective interactions (optical potentials) have to enter reaction descriptions when possible reaction channels are eliminated from explicit consideration. The program will address the challenge of developing effective interactions that have predictive power in the regime of exotic nuclei, where data is scarce, and seek strategies for anchoring these interaction in ab initio, microscopic, or effective theories.

• Improving structure inputs to reaction approaches.
  To achieve more reliable predictions for unstable nuclei, it is important that ab initio theories inform/replace current microscopic models for medium-mass systems, while microscopic methods need to replace the phenomenology used for heavier systems. The program will review recent developments in nuclear structure theory and identify avenues for integrating improved structure information into new and existing reaction theories and codes.

• Integrating relevant reaction processes into a coherent framework.
  For reactions involving the lightest of elements, a truly integrated structure and reaction description is being achieved, while for medium mass and heavy systems this remains to be done. The program will discuss the interplay between various reaction processes (direct, semi-direct, pre-equilibrium, and compound reactions) and consider options for developing descriptions that treat these processes in a better integrated manner.

Overall, we expect this program to provide a clearer picture of the capabilities and gaps of the theory, as well as strategies for moving forward. We anticipate our conclusions to be informed by (existing and anticipated) experimental capabilities and marked by an awareness of the data needs of inter-disciplinary efforts, e.g. in astrophysics.

Workshop Format and Topic

The workshop Nuclear Reactions: A Symbiosis between Experiment, Theory and Applications will be coordinated by J. Blackmon (LSU), N. Scielzo (LLNL), and J. Escher (LLNL). This workshop is dedicated to the intersection of experiment, theory, and applications. It will focus on connecting theory developments to experimental advances and data needs for astrophysics and other applications.

A workshop format will be adopted with a series of talks (overview as well as specific) each day and opportunities for discussions. The presentations will cover experimental needs and capabilities and outline the needs of the astrophysics and nuclear data communities. Discussions will aim at identifying gaps in existing theories and identify possible experimental tests of current and planned theories. Focus areas will be explored where (future) experimental work can provide benchmark results that make it possible to compare different theoretical methods and test their reliability. We also plan to identify immediate applications of new theoretical developments, e.g. reaction measurements at radioactive beam facilities.

There will be a $40 registration fee to attend the workshop. The registration fee includes participation in the workshop, lectures, and coffee breaks.