Case Study 1: Ten Questions for the Next Decade of Nuclear Physics

The Challenge of Prioritization

In 2023, the U.S. nuclear physics community completed its decadal Long Range Plan (LRP), a comprehensive assessment of the field's scientific priorities and resource needs submitted to the Department of Energy and the National Science Foundation. The process involved hundreds of physicists in town halls, white papers, working groups, and a final writing committee. The LRP is not merely an academic exercise — it directly influences which facilities are built, which experiments are funded, and which scientific directions receive support for the next decade.

The LRP process forces the community to confront a difficult question: given finite resources, which scientific questions should receive the highest priority?

This case study asks you to engage with that question directly.

The Ten Questions

Below are the ten open questions discussed in Chapter 33, summarized with their key experimental requirements and approximate costs:

Note: cost estimates are approximate and represent the nuclear physics community's share, not total project costs for multi-agency or international facilities.

The 2023 Long Range Plan Priorities

The actual 2023 LRP identified the following top priorities (in order):

1. Capitalize on the investment in FRIB by funding a world-class experimental program and the FRIB400 energy upgrade.
2. Construct the Electron-Ion Collider (EIC) at Brookhaven National Laboratory.
3. Mount a tonne-scale neutrinoless double beta decay experiment in the United States.
4. Invest in a comprehensive program of small- and mid-scale experiments across the field.
5. Expand and strengthen the nuclear physics workforce, with emphasis on diversity, equity, and inclusion.

These priorities reflect a combination of scientific impact, readiness, U.S. leadership, and broader workforce considerations.

Analysis Questions

Part A: Scientific Prioritization

1. Consider Questions 1, 4, 9, and 10 — all of which are primarily addressed by FRIB. What makes a single facility so central to so many different scientific questions? Is this concentration of scientific potential a strength or a vulnerability?

2. The EIC (Question 8) was the second-highest priority despite addressing primarily one scientific question (the nucleon spin puzzle and related aspects of QCD). What justifies this high ranking? Consider the uniqueness of the measurement, the lack of alternative facilities, and the fundamental nature of the question.

3. The $0\nu\beta\beta$ experiments (Question 5) ranked third. The observation of neutrinoless double beta decay would be one of the most important discoveries in physics — it would prove that the neutrino is a Majorana particle, that lepton number is violated, and would constrain the absolute neutrino mass. Why might such a high-impact discovery question rank below FRIB operations and EIC construction?

4. Commercial fusion energy (Question 7) was not among the top nuclear physics priorities, despite its enormous societal importance. Why? Consider the distinction between the nuclear physics community's mission and the broader energy research portfolio.

Part B: Trade-offs and Constraints

5. The total U.S. nuclear physics budget (DOE Office of Nuclear Physics) is approximately $750 million per year. FRIB operations alone consume roughly $100M/yr, and EIC construction will cost approximately $2B over a decade. How do these numbers constrain the community's ability to pursue multiple priorities simultaneously?

6. Some questions (like dark matter detection, Question 6) lie at the boundary between nuclear physics and particle physics. How should funding responsibility be shared between communities? What happens when a question falls between two agencies' primary missions?

7. The LRP explicitly prioritized workforce development. Some might argue that workforce is an administrative concern, not a scientific one. Make the case that workforce development is in fact a scientific priority — that the diversity and size of the nuclear physics workforce directly affects the quality and scope of the science.

Part C: Your Priorities

8. If you were given $100M per year in new nuclear physics funding (approximately a 13% increase to the current budget), how would you allocate it? Choose at most three of the ten questions to prioritize, and justify your choices based on: - Scientific impact (how transformative would an answer be?) - Feasibility (can the question be answered with current technology?) - Timeliness (is there a window of opportunity?) - Broader impacts (societal, technological, or educational benefits)

9. Some open questions may never be fully answered in your lifetime. Which of the ten questions do you think is least likely to be resolved by 2050? Which is most likely? Justify your assessments.

10. The 2023 LRP is a U.S. document. How would the prioritization look different from the perspective of the European or Asian nuclear physics communities? Consider the existing facilities, funding structures, and scientific traditions in those regions.

Lessons from the Exercise

The LRP process illustrates several principles about how science is organized and funded:

• Science is a social enterprise. Prioritization requires not just intellectual judgment but negotiation, consensus-building, and strategic thinking about institutional strengths and weaknesses.

• Facilities take decades. The EIC was first proposed in the early 2000s, approved for construction in 2020, and will produce its first physics data in the mid-2030s. FRIB's planning began in the 1990s. The decisions we make today determine the science that will be done in the 2040s and beyond.

• Opportunity costs are real. Every dollar spent on one experiment is a dollar not spent on another. The LRP process forces the community to confront these trade-offs explicitly rather than avoiding them.

• The most important question is not always the highest priority. Priority depends on feasibility, cost, and the existence of alternatives — not just on scientific importance. A transformative question that cannot be addressed with current technology may rank below a less dramatic question that is ripe for progress.

This case study has no single correct answer. The point is to practice the kind of scientific judgment that working physicists exercise when they shape the direction of their field.