Building for Discovery Strategic Plan for U.S. Particle Physics in the Global Context Report of the Particle Physics Project Prioritization Panel (P5) May 2014 Report of the Particle Physics Project Prioritization Panel i Preface Panel reports usually convey their results logically and dispas- to our community, to those who charged us, and to scientists sionately, with no mention of the emotional, soul-searching in other fields. Our community’s passion, dedication, and entre- processes behind them. We would like to break with tradition preneurial spirit have been inspirational. Therefore, to our to share some behind-the-scenes aspects and perspectives. colleagues across our country and around the world, we say a heartfelt thank you. Every request we made received a thought- This is a challenging time for particle physics. The science is ful response, even when the requests were substantial and the deeply exciting and its endeavors have been extremely suc- schedules tight. A large number of you submitted inputs to cessful, yet funding in the U.S. is declining in real terms. This the public portal, which we very much appreciated. report offers important opportunities for U.S. investment in science, prioritized under the tightly constrained budget sce- In our deliberations, no topic or option was off the table. Every narios in the Charge. We had the responsibility to make the alternative we could imagine was considered. We worked by tough choices for a world-class program under each of these consensus—even when just one or two individuals voiced con- scenarios, which we have done. At the same time, we felt the cerns, we worked through the issues. responsibility to aspire to an even bolder future. These are not contradictory responsibilities: an annual budget is a balance Wondrous projects that address profound questions inspire sheet, but investment in fundamental research is a powerful and invigorate far beyond their specific fields, and they lay expression that our culture and economy have greater potential the foundations for next-century technologies we can only in the long run. Our society’s capacity to grow is limited only begin to imagine. Particle physics is an excellent candidate by our collective imagination and resolve to make long-term for such investments. Historic opportunities await us, enabled investments that can lead to fundamental, game-changing by decades of hard work and support. Our field is ready to discoveries, even in the context of constrained budgets. move forward. We were given complex issues to resolve. We listened carefully Respectfully submitted, Steve Ritz, chair Marcel Demarteau Francis Halzen Lia Merminga Kevin Pitts University of California, Argonne National Laboratory University of TRIUMF University of Illinois Santa Cruz Wisconsin-Madison at Urbana-Champaign Hiroaki Aihara Scott Dodelson JoAnne Hewett Toshinori Mori Kate Scholberg University of Tokyo Fermi National Accelerator SLAC National Accelerator University of Tokyo Duke University Laboratory and Laboratory University of Chicago Martin Breidenbach Jonathan L. Feng Wim Leemans Tatsuya Nakada Rick van Kooten SLAC National Accelerator University of California, Lawrence Berkeley National Swiss Federal Institute Indiana University Laboratory Irvine Laboratory of Technology in Lausanne (EPFL) Bob Cousins Bonnie Fleming Joe Lykken Steve Peggs Mark Wise University of California, Yale University Fermi National Accelerator Brookhaven National California Institute of Los Angeles Laboratory Laboratory Technology André de Gouvêa Fabiola Gianotti Dan McKinsey Saul Perlmutter Andy Lankford, ex officio Northwestern University European Organization for Yale University University of California, University of California, Nuclear Research (CERN) Berkeley Irvine Report of the Particle Physics Project Prioritization Panel iii Contents Executive Summary v Chapter 1: Introduction 1 1.1: Particle Physics is a Global Field for Discovery — 2 1.2: Brief Summary of the Science Drivers and Main Opportunities — 3 1.3: Criteria — 6 Chapter 2: Recommendations 7 2.1: Program-wide Recommendations — 8 2.2: Project-specific Recommendations — 10 2.3: Funding Scenarios — 15 2.4: Enabling R&D — 19 Chapter 3: The Science Drivers 23 3.1: Use the Higgs Boson as a New Tool for Discovery — 25 3.2: Pursue the Physics Associated with Neutrino Mass — 29 3.3: Identify the New Physics of Dark Matter — 35 3.4: Understand Cosmic Acceleration: Dark Energy and Inflation — 39 3.5: Explore the Unknown: New Particles, Interactions, and Physical Principles — 43 3.6: Enabling R&D and Computing — 46 Chapter 4: Benefits and Broader Impacts 49 Appendices 53 Appendix A: Charge — 54 Appendix B: Panel Members — 57 Appendix C: Process and Meetings — 58 Appendix D: Snowmass Questions — 63 Appendix E: Full List of Recommendations — 64 Report of the Particle Physics Project Prioritization Panel v Executive Summary Particle physics explores the fundamental constituents of mat- Snowmass, the yearlong community-wide study, preceded the ter and energy. It reveals the profound connections underlying formation of our new P5. A vast number of scientific opportu- everything we see, including the smallest and the largest struc- nities were investigated, discussed, and summarized in tures in the Universe. The field is highly successful. Investments Snowmass reports. We distilled those essential inputs into five have been rewarded recently with discoveries of the heaviest intertwined science Drivers for the field: elementary particle (the top quark), the tiny masses of neutri- • Use the Higgs boson as a new tool for discovery nos, the accelerated expansion of the Universe, and the Higgs boson. Current opportunities will exploit these and other dis- • Pursue the physics associated with neutrino mass coveries to push the frontiers of science into new territory at • Identify the new physics of dark matter the highest energies and earliest times imaginable. For all these reasons, research in particle physics inspires young people to • Understand cosmic acceleration: dark energy and inflation engage with science. • Explore the unknown: new particles, interactions, and physical principles. Particle physics is global. The United States and major players in other regions can together address the full breadth of the The vision for addressing these Drivers with a prioritized set field’s most urgent scientific questions if each hosts a unique of projects, including their approximate timescales and how world-class facility at home and partners in high-priority facil- they fit together, was developed using a set of selection criteria. ities hosted elsewhere. Strong foundations of international The Drivers, which are intertwined, are not prioritized. Instead, cooperation exist, with the Large Hadron Collider (LHC) at the prioritization is in the selection and timing of the specific CERN serving as an example of a successful large international projects, which are categorized as large, medium, or small based science project. Reliable partnerships are essential for the suc- on the construction costs to the particle physics program. cess of international projects. Building further international cooperation is an important theme of this report, and this To enable an optimal program, given recent scientific results perspective is finding worldwide resonance in an intensely and funding constraints, and using our criteria, we recommend competitive field. some projects not be implemented, others be delayed, and some existing efforts be reduced or terminated. Having made Choices are required. Ideas for excellent new projects far exceed these choices, the field can move forward immediately with a what can be executed with currently available resources. The prioritized, time-ordered program, which is summarized in Table 1 U.S. must invest purposefully in areas that have the biggest and includes the following features: impacts and that make most efficient use of limited resources. Since the 2008 Particle Physics Project Prioritization Panel • The enormous physics potential of the LHC, which will be (P5) report, two major U.S. particle physics facilities have ter- entering a new era with its planned high-luminosity upgrades, minated operations, and inflation-adjusted funding in the U.S. will be fully exploited. The U.S. will host a world-leading neutrino for particle physics has continued to decline. In addition, pri- program that will have an optimized set of short- and long-base- marily because of earlier strong investments, landmark dis- line neutrino oscillation experiments, and its long-term focus coveries have been made that inform choices for future direc- is a reformulated venture referred to here as the Long Baseline tions. A new P5 panel was therefore charged to provide “an Neutrino Facility (LBNF). The Proton Improvement Plan-II (PIP-II) updated strategic plan for the U.S. that can be executed over project at Fermilab will provide the needed neutrino physics a ten-year timescale, in the context of a twenty-year global capability. To meet budget constraints, physics needs, and read- vision for the field.” The Charge calls for planning under two iness criteria, large projects are ordered by peak construction specific budget Scenarios, reflecting current fiscal realities, as time: the Mu2e experiment, the high-luminosity LHC upgrades, well as for an additional unconstrained Scenario. and LBNF. Building for Discovery: Strategic Plan for U.S. Particle Physics in the Global Context vi • The interest expressed in Japan in hosting