«29 May 2008 Three frontiers of research in particle physics form an interlocking framework that addresses fundamental questions about the laws of ...»
US Particle Physics:
A Strategic Plan
for the Next Ten Years
Report of the Particle
29 May 2008
Three frontiers of research in particle physics form
an interlocking framework that addresses
fundamental questions about the laws of nature
and the cosmos.
US Particle Physics:
A Strategic Plan
for the Next Ten Years
Report of the Particle Physics Project Prioritization Panel 29 May 2008 i In November 2007, at the request of the Office of High Energy Physics of the About Department of Energy and the National Science Foundation, the High Energy Physics Advisory Panel reconstituted the Particle Physics Project Prioritization Panel for the the purpose of developing a plan for US particle physics for the coming decade under a variety of budget assumptions. Appendix A of this report gives the charge to the P5 panel; Appendix B lists its membership. To carry out this charge the panel organized P5 Subpanel three information-gathering meetings, at Fermilab in January, at Stanford Linear Accelerator Center in February, and at Brookhaven National Laboratory in March of
2008. Appendix C gives the agendas for these meetings. Besides talks by experts in the field, each of the three meetings included a Town Meeting, an open session where members of the community could voice their advice, suggestions and concerns to the panel. The panel also invited letters from the worldwide particle physics community, to offer their points of view for consideration. The panel held an additional meeting in early April to put together the first draft of this report.
The strategic plan and recommendations contained in this report, if adopted by HEPAP, are advisory input to the Department of Energy and the National Science Foundation. The actual design and implementation of any plan in these agencies is the responsibility of program management.
Report of the Particle Physics Project Prioritization Panel 1 Executive Summary 1 Table The Three Frontiers of Particle Physics 9 of 2 Particle Physics in the National and International Context 13
2.1 Long-Term Value of Research in Fundamental Sciences 13
2.2 Benefits to Society 14 Contents
2.3 The International Context 18 3 The Frontiers of our Science: Beyond the Standard Model 21
3.1 The Energy Frontier: Exploring the Terascale 21
3.2 The Intensity Frontier: Neutrino Physics and Precision Measurement 34
3.3 The Cosmic Frontier 46 4 The Deep Underground Science and Engineering Laboratory—DUSEL 57
1 ExECUTIVE SUMMARy Particle physics is a central component of the physical sciences, focused on the fundamental nature of matter and energy, and of space and time. Discoveries in this field, often called high-energy physics, will change our basic understanding of nature.
The Standard Model of particle physics provides a remarkably accurate description of elementary particles and their interactions. However, experiment and observation strongly point to a deeper and more fundamental theory that breakthroughs in the coming decade will begin to reveal.
To address the central questions in particle physics, researchers use a range of tools
and techniques at three interrelated frontiers:
• he Energy Frontier, using high-energy colliders to discover new particles and T directly probe the architecture of the fundamental forces.
• T he Intensity Frontier, using intense particle beams to uncover properties of neutrinos and observe rare processes that will tell us about new physics beyond the Standard Model.
• T he Cosmic Frontier, using underground experiments and telescopes, both ground and space based, to reveal the natures of dark matter and dark energy and using high-energy particles from space to probe new phenomena.
As described in the box on pages 9-11, these three frontiers form an interlocking framework that addresses fundamental questions about the laws of nature and the cosmos. These three approaches ask different questions and use different techniques, but they ultimately aim at the same transformational science.
The changing context Recent reports, including the National Research Council’s “Revealing the Hidden Nature of Space and Time” (the EPP2010 report) and earlier P5 reports, have discussed the outlook for the field of particle physics in the United States. The scientific priorities have not changed since those reports appeared, but the context for the scientific opportunities they describe has altered.
Particle physics in the United States is in transition. Two of the three high-energy physics colliders in the US have now permanently ceased operation. The third, Fermilab’s Tevatron, will turn off in the next few years. The energy frontier, defined for decades by Fermilab’s Tevatron, will move to Europe when CERN’s Large Hadron Collider begins operating. American high-energy physicists have played a leadership role in developing and building the LHC program, and they constitute a significant fraction of the LHC collaborations—the largest group from any single nation. About half of all US experimental particle physicists participate in LHC experiments.
1 Executive Summary
As this transition occurs, serious fiscal challenges change the landscape for US particle physics. The large cost estimate for the International Linear Collider, a centerpiece of previous reports, has delayed plans for a possible construction start and has led the particle physics community to take a fresh look at the scientific opportunities in the decade ahead. The severe funding reduction in the Omnibus Bill of December 2007 stopped work on several projects and had damaging impacts on the entire field. The present P5 panel has developed a strategic plan that takes these new realities into account.
Overall recommendation Particle physics explores the fundamental constituents of matter and energy and the forces that govern their interactions. Great scientific opportunities point to significant discoveries in particle physics in the decade ahead.
Research in particle physics has inspired generations of young people to engage with science, benefiting all branches of the physical sciences and strengthening the
scientific workforce. To quote from the EPP2010 report:
“A strong role in particle physics is necessary if the United States is to sustain its leadership in science and technology over the long term.”
The present P5 panel therefore makes the following overall recommendation:
The panel recommends that the US maintain a leadership role in world-wide particle physics. The panel recommends a strong, integrated research program at the three frontiers of the field: the Energy Frontier, the Intensity Frontier and the Cosmic Frontier.
The Energy Frontier Experiments at energy-frontier accelerators will make major discoveries about particles and their interactions. They will address key questions about the physical nature of the universe: the origin of particle masses, the existence of new symmetries of nature, the existence of extra dimensions of space, and the nature of dark matter. Currently, the Tevatron at Fermilab is the highest-energy collider operating in the world.
The panel recommends continuing support for the Tevatron Collider program for the next one to two years, to exploit its potential for discoveries.
In the near future, the Large Hadron Collider at CERN in Geneva, Switzerland will achieve much higher collision energies than those of any previous accelerator, to explore the energy range we call the Terascale. The LHC represents the culmination of more than two decades of international effort and investment, with major US involvement. Experiments at the LHC are poised to make exciting discoveries that will change our fundamental understanding of nature. Significant US participation in the full exploitation of the LHC has the highest priority in the US high-energy physics program.
The panel recommends support for the US LHC program, including US involvement in the planned detector and accelerator upgrades.
The international particle physics community has reached consensus that a full understanding of the physics of the Terascale will require a lepton collider as well as the LHC. The panel reiterates the importance of such a collider. In the next few years, results from the LHC will establish its required energy. If the optimum initial energy proves to be at or below approximately 500 GeV, then the International Linear Collider is the most mature and ready-to-build option with a construction start possible in the next decade. A requirement for initial energy much higher than 500
2 Report of the Particle Physics Project Prioritization Panel
GeV will mean considering other collider technologies. The cost and scale of a lepton collider mean that it would be an international project, with the cost shared by many nations. International negotiations will determine the siting; the host will be assured of scientific leadership at the energy frontier. Whatever the technology of a future lepton collider, and wherever it is located, the US should plan to play a major role.
For the next few years, the US should continue to participate in the international R&D program for the ILC to position the US for an important role should the ILC be the choice of the international community. The US should also participate in coordinated R&D for the alternative accelerator technologies that a lepton collider of higher energy would require.
The panel recommends for the near future a broad accelerator and detector R&D program for lepton colliders that includes continued R&D on ILC at roughly the proposed Fy2009 level in support of the international effort. This will allow a significant role for the US in the ILC wherever it is built. The panel also recommends R&D for alternative accelerator technologies, to permit an informed choice when the lepton collider energy is established.
The Intensity Frontier Recent striking discoveries make the study of the properties of neutrinos a vitally important area of research. Measurements of the properties of neutrinos are fundamental to understanding physics beyond the Standard Model and have profound consequences for the evolution of the universe. The latest developments in accelerator and detector technology make possible promising new scientific opportunities in neutrino science as well as in experiments to measure rare processes. The US can build on the unique capabilities and infrastructure at Fermilab, together with DUSEL, the Deep Underground Science and Engineering Laboratory proposed for the Homestake Mine in South Dakota, to develop a world-leading program of neutrino science.
Such a program will require a multi-megawatt-powered neutrino source at Fermilab.
The panel recommends a world-class neutrino program as a core component of the US program, with the long-term vision of a large detector in the proposed DUSEL and a high-intensity neutrino source at Fermilab.
The panel recommends an R&D program in the immediate future to design a multi-megawatt proton source at Fermilab and a neutrino beamline to DUSEL and recommends carrying out R&D on the technologies for a large multi-purpose neutrino and proton decay detector.
Construction of these facilities could start within the 10-year period considered by this report.
A neutrino program with a multi-megawatt proton source would be a stepping stone toward a future neutrino source, such as a neutrino factory based on a muon storage ring, if the science eventually requires a more powerful neutrino source. This in turn could position the US program to develop a muon collider as a long-term means to return to the energy frontier in the US.
The proposed DUSEL is key to the vision for the neutrino program. It is also central to nonaccelerator experiments searching for dark matter, proton decay and neutrinoless double beta decay. DOE and NSF should define clearly the stewardship responsibilities for such a program.
The panel endorses the importance of a deep underground laboratory to particle physics and urges NSF to make this facility a reality as rapidly as possible. Furthermore the panel recommends that DOE and NSF work together to realize the experimental particle physics program at DUSEL.
Scientific opportunities through the measurement of rare processes include experiments to search for muon-to-electron conversion and rare-kaon and B-meson decay.
Such incisive experiments, complementary to experiments at the LHC, would probe the Terascale and possibly much higher energies.
The panel recommends funding for measurements of rare processes to an extent depending on the funding levels available, as discussed in more detail in Sections 3.2.2 and 7.2.3.
The Cosmic Frontier Although 95 percent of the universe appears to consist of dark matter and dark energy, we know little about either of them. The quest to elucidate the nature of dark matter and dark energy is at the heart of particle physics—the study of the basic constituents of nature, their properties and interactions.
The US is presently a leader in the exploration of the Cosmic Frontier. Compelling opportunities exist for dark matter search experiments, and for both ground-based and space-based dark energy investigations. In addition, two other cosmic frontier areas offer important scientific opportunities: the study of high-energy particles from space and the cosmic microwave background.
The panel recommends support for the study of dark matter and dark energy as an integral part of the US particle physics program.
The panel recommends that DOE support the space-based Joint Dark Energy Mission, in collaboration with NASA, at an appropriate level negotiated with NASA.
The panel recommends DOE support for the ground-based Large Synoptic Survey Telescope program in coordination with NSF at a level that depends on the overall program budget.
The panel further recommends joint NSF and DOE support for direct dark matter search experiments.
The panel recommends limited R&D funding for other particle astrophysics projects and recommends establishing a Particle Astrophysics Science Advisory Group.