Input to the SCAC Facilities Subcommittee from the U.S. Muon Collider Collaboration
This document provides the U.S. Muon Collider Collaboration's input to the SCAC Facilities Subcommittee, outlining the scientific case, necessary R&D roadmap, and strategic relevance of a future Muon Collider to U.S. facility planning for 2026–2036 while emphasizing workforce development and international synergies.
Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
In the vast landscape of modern physics, scientists are constantly searching for the next great leap in understanding the universe. For decades, the most powerful tool for this search has been the particle collider, a massive machine that smashes tiny particles together at incredible speeds to recreate the conditions of the early universe. The current champion, the Large Hadron Collider, has already revealed the Higgs boson, a particle that explains how other things get their mass. However, the universe still holds deep mysteries, such as the nature of dark matter and the reason why the universe is made of matter rather than antimatter. To solve these puzzles, physicists need to reach higher energy levels than ever before. One proposed path forward involves a machine built around muons, a particle similar to an electron but much heavier. Because muons are heavy, they can be accelerated to extremely high energies without losing as much energy as lighter particles would, potentially opening a window to physics at scales far beyond what current machines can see.
A group of scientists from across the United States has recently submitted a detailed plan to the Strategic Planning Committee for Accelerator Facilities, outlining how the country can prepare for the possibility of building such a machine. Their proposal does not call for the immediate construction of a giant collider, which would be a massive and risky undertaking. Instead, they argue that the next decade should be dedicated to a carefully staged program of research and development. The core of their argument is that before a full-scale facility can be built, the team must prove that the most difficult parts of the technology actually work. They propose starting with small-scale tests of individual components, known as micro-demonstrators, spread across various universities and national laboratories. These tests would check things like powerful magnets, radio-frequency cavities that speed up particles, and the complex systems needed to cool the muon beams. By testing these pieces separately first, the team hopes to reduce the technical risks and refine the design before committing to a larger project.
The plan envisions a progression from these small tests to a larger, integrated facility called a macro-demonstrator. This intermediate machine would not be a full collider, but it would be a working prototype capable of producing and cooling muon beams on a significant scale. The scientists believe this facility could also serve as a powerful tool for other areas of physics, such as studying neutrinos or dark matter, even before a full collider is built. The proposal emphasizes that the United States must maintain its expertise in this field to remain a leader in global science. If the country waits too long to develop these technologies, it risks losing the skilled workforce and engineering knowledge required to build such a complex machine. The authors point out that while the basic idea of cooling muons has been tested in the past, putting together a full system that works under realistic engineering conditions has never been done. This is the primary hurdle that needs to be cleared.
The document also highlights the broader benefits of this research program. The technologies needed to build a muon collider, such as high-power magnets and advanced radiation detectors, have applications in other fields, including medical imaging and nuclear security. By investing in this research now, the United States could advance capabilities across the entire Office of Science, not just for particle physics. The scientists are clear that they are not asking for a construction budget yet. They are asking for a coordinated plan to fill a gap in the current research portfolio. They want to ensure that by the time a decision is made to build a collider in the future, the technology will be ready, the costs will be understood, and the scientific case will be solid. Their goal is to keep the option of hosting a world-leading energy frontier facility alive for the next generation of scientists, ensuring that the United States remains at the forefront of exploring the fundamental laws of nature.
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