Revealing the Hidden Nature of Space and Time Charting the Course for Elementary Particle Physics (in the U.S.) Committee on Elementary Particle Physics in the 21 st Century (EPP 2010) National Research Council of the National Academies

National Research Council: part of National Academy of Sciences. Mandate from US Congress (1863) to advise federal government. Charge to this committee: 1. Identify, articulate, and prioritize the scientific questions and opportunities that define elementary-particle physics. 2. Recommend a 15-year implementation plan with realistic, ordered priorities to realize these opportunities. General feeling: U.S. particle physics is at a crossroads. Many projects terminate in Some bold plans are needed.

Committee: 22 members, of which: 2 industry 7 non-HEP academic scientists 13 HEP physicists “The composition was something of an experiment… As a result, a good deal of education was necessary…” “Members from outside particle physics posed challenging questions to those inside the field and listened carefully to arguments. The result was an overall sharpening of everyone’s thinking as well as stronger connections to a broader context” “For the non-physicists on the committee, the task was both intellectually exciting and sobering. Simply stated, we were not fully aware of the challenge faced by the US particle physics program in sustaining its tradition of leadership…”

3 questions in particle physics: Can the forces between particles be understood in a unified framework? What do the properties of particles reveal about the nature and the origin of matter? What is dark energy, and how has quantum mechanics influenced the structure of the universe? Top priority: exploration of the Terascale. Particle interactions at the scale of a TeV or higher. LHC. ILC should be the next major collider. But: these two should never completely exhaust the budget.

6 (findings and) action items: 1.The highest priority for the U.S. national effort in elementary particle physics should be to continue to be an active partner in realizing the physics potential of the LHC experimental program. Number of U.S. researchers at the LHC will increase U.S. support should keep pace with level of involvement and need to maintain detectors. Full support will require a larger share of existing resources than at present. As potential upgrades are motivated and defined through scientific results, U.S. should consider in-kind contributions as appropriate.

2.An aggressive approach to the realization of the ILC is the central element in a new strategic plan for the U.S. program in particle physics. The U.S. should launch a major program of R&D, design, industrialization, and managing and financing studies of the ILC accelerator and detectors. Consensus of community: ILC next major experimental facility Global Design Effort: reference design with baseline costs: end 2006 full technical design 2009 Decision on ILC should be made no later than 2010 Accelerator commitment from the U.S.: $300M - $500M in 5 years before decision Detector R&D: $50M U.S. should become leading center for ILC R&D. International governance structure and cost-sharing agreement to be pursued.

3.The United States should announce its strong interest to become the host country for the ILC and should undertake the necessary work to provide a viable site and mount a compelling bid. It is not certain that the aggressive pursuit of ILC R&D and a hosting bid would ensure construction or a site in the U.S. However, alternatives to this strategy will not achieve a leadership position. The committee believes that the ILC represents so tremendous an opportunity that is must be pursued vigorously and whole-heartedly. As a host country, U.S. would be expected to commit to a higher level of cost sharing % of the total costs would be for conventional construction activities at the site. Locating the ILC near Fermilab would provide a vibrant center. The existing infrastructure as well as assessments of its geological stability and useable space make it a logical choice. As the only national laboratory devoted solely to particle physics, Fermilab’s top priority should be to secure the ILC.

4.Extraordinary opportunities in astrophysics and cosmology research: probe energies and conditions not available at accelerators Top scientific questions: - direct detection of dark matter in terrestrial laboratories - cosmic microwave background polarization measurement - measurement of key properties of dark energy Scientific priorities at the interface of particle physics, astrophysics and cosmology should be determined through a mechanism jointly involving NSF, DOE, and NASA, with emphasis on DOE and NSF participation in projects where the intellectual and technological capabilities of particle physicists can make unique contributions. The committee recommends that an increased share of the current U.S. elementary particle physics research budget should be allocated to address the questions identified above. Factor 2-3 ! (but was relatively small…)

5.The committee recommends that the properties of neutrinos be determined through a well-coordinated, staged program of experiments developed with international planning and cooperation. -Investigate nature of neutrino mass (0 decay) -Initiate international multiparty study to explore feasibility of joint, rather than parallel, efforts in accelerator-based neutrino experiments. -Longer term goals should include CP-violation in lepton sector and searches for proton decay. There may be a valuable synergy between these important objectives. Experiments in this area should be globally rationalized from start to finish. Avoid unnecessary duplication. Certain neutrino physics and proton decay experiments might be based outside U.S.

6.U.S. participation in large-scale high-precision experiments that probe particle physics beyond the Standard Model should continue, but the level of support that can be sustained will have to be very sensitive to the overall budget picture. Only very limited participation will be feasible in budget scenarios with little or no real growth. Participation in inexpensive, small-scale, high-precision measurements should be encouraged in any budget scenario. Super B-factory, lepton flavor violation experiments, Rare K decays, g-2, electric dipole moments Some of these can be small-scale Super B-factory might be based outside U.S.

A B C D Upon termination of Tevatron, BaBar, RHIC, some funds freed Proposed American Competitiveness Initiative: 8% more for particle physics FY 2007

Some budget remarks: Scenario A: support for LHC, ILC, expand particle astrophysics. But little left for neutrinos, precision experiments. If ILC were hosted by the U.S, additional funding is needed. Scenario B jeopardizes full exploration of the Terascale. U.S. would be a partner, not a leader, and would not host ILC. Efforts in particle astrophysics could be expanded; neutrinos studied abroad. Scientific influence of U.S. in particle physics would be much diminished. Scenario C would go a long way towards realizing LHC, ILC studies and realistic bid, particle astrophysics and a fuller neutrino program. Actually hosting the ILC would still need more. In scenario D, U.S. would make a strong presence in all fields. (The committee considered strategies that abandoned accelerators altogether, but rejected them because they did not lead to a program of sufficient health and vitality to sustain itself)