For nearly a century, physicists have been colliding particles to gain insight into the nature of our physical world. This approach has driven some of the greatest breakthroughs in physics, including the discoveries of the top quark at Fermi National Accelerator Laboratory’s Tevatron accelerator and the Higgs boson at CERN’s Large Hadron Collider. Now, a new frontier in particle physics is beckoning: the potential to unlock scientific knowledge by colliding subatomic particles called muons. Once constructed, a muon collider could reveal new physical phenomena that revolutionize our understanding of energy, matter, space and time.
Muons, which belong to the lepton family along with electrons, tau leptons and corresponding neutrinos, are about 200 times heavier than electrons. Unlike protons —composite particles made of quarks and gluons — muons are fundamental particles with no known internal structure.
Short-lived particles
In particle colliders, high-energy collisions directly convert energy into new particles, demonstrating Einstein’s famous equation, E = mc2, which links matter and energy. One of the main advantages of the muon collider is that it will directly translate energy from the particle collisions into new particles without energy being transferred elsewhere.
Since muons are not made of smaller constituent particles like protons or charged atoms, their collisions would produce a cleaner dataset. In contrast, when protons or charged atoms collide, part of the energy is wasted on ejecting secondary particles from their internal structure rather than being fully used to generate new particles.
As a result, a muon collider will use a smaller footprint and less energy to generate new particles for study. For instance, a more power-efficient, 10 TeV muon collider could yield data comparable in physics reach to a 100 TeV Hadron Collider, and it would be approximately five times smaller in size.
However, there’s a significant challenge. Muons exist for just a few microseconds, making it difficult to harness their potential for study.
“While the concept of the muon collider dates back to the 1970s, practical obstacles kept it theoretical,” said Sergo Jindariani, a Fermilab scientist. “Recent advances in technology have renewed interest in the muon collider.”
Improvements in accelerator and detector technologies have brought new possibilities for physics research. Superconducting cavities now accelerate particles to higher energies, superconducting magnets can generate stronger magnetic fields, and the integration of precision timing capabilities and artificial intelligence into future detectors will revolutionize their capabilities.
While these technologies are advanced by today’s standards, experts agree that even further breakthroughs are required before a muon collider can be built. A collaboration of theorists, experimentalists and accelerator physicists will be essential to developing the tools and infrastructure needed to make the collider work.
A new generation
To jumpstart this ambitious project, around 300 researchers from across the nation gathered at Fermilab last August to discuss the technical challenges, build educational initiatives for the scientific community, and garner support for developing and building the collider.
“There was an especially large contingent of early-career researchers drawn to the promise of pioneering new physics,” said Jindariani. “The earliest we can start building the collider is maybe in the 2040s. This machine is really for future generations to pick up and conduct physics with.”
Kiley Kennedy is a postdoctoral researcher at Princeton University who works on the CMS detector at the Large Hadron Collider, and she attended the inaugural Muon Collider workshop.
“I came into particle physics as an undergrad in 2015, and I didn’t build the detector I work on,” said Kennedy. “I inherited it. It’s really cool to think about building a detector that hopefully I will be able to use.”
Kennedy added that senior researchers in the field might not have the opportunity to work on the collider when it’s fully constructed.
“I think they are paying it forward,” added Kennedy. “One quote that resonates with me is from Isaac Newton: ‘If I have seen further, it is by standing on the shoulders of giants.’ That’s really how I feel when I think about collider physics from the LHC to muon colliders.”
Condensing muons
One of the toughest technological challenges in colliding muons is condensing them to increase the number of collisions in the collider. Muons scatter after they are generated. Condensing the muons is like starting with a diffuse cloud the size of a basketball and compressing it into a smooth, dense cluster the size of a marble.
A critical step toward building a muon collider is developing a prototype of a muon ionization cooling demonstrator to help researchers tackle the challenge of condensing muons. Once completed, the prototype will harness a sequence of powerful magnets, absorber materials and cavities that contain electromagnetic energy to precisely squeeze the muons closer together, increasing the number of collisions between groups of muons.
A second, smaller workshop in October helped researchers conceptualize the details of this prototype, including the required equipment, space and timelines.
“The International Workshop on Ionization Cooling Demonstrator set the stage for building a prototype cooling system called the demonstrator,” said Diktys Stratakis, a Fermilab scientist. “Building the demonstrator would be a major step toward the muon collider.”
The International Muon Collider Collaboration aims to have the demonstrator operating by the 2030s. While the collaboration is international in scope, the ionization cooling demonstrator and the eventual full-scale muon collider could ultimately be constructed at Fermilab, bringing the next generation of particle physics capabilities to the United States.
Fermi National Accelerator Laboratory is America’s premier national laboratory for particle physics and accelerator research. Fermi Forward Discovery Group manages Fermilab for the U.S. Department of Energy Office of Science. Visit Fermilab’s website at www.fnal.gov and follow us on social media.
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Beginning today, photographers are invited to apply for a spot to capture exclusive and behind-the-scenes photographs of locations at Fermi National Accelerator Laboratory in Batavia, Illinois. Professional and amateur photographers will be able to explore and take pictures of scientific experiments and equipment in five designated research areas that are not accessible to the public.
The 2025 Global Physics Photowalk is a photo competition that begins with a local contest at each of the participating laboratories. As part of this, Fermilab will offer a day this summer for 25 photographers to tour the lab and take photos, which can then be submitted to the local contest. Fermilab judges will submit three of the local winners to the worldwide Global Physics Photowalk competition. The Interactions Collaboration will announce a shortlist of global finalists in September, and the winners will be selected by a jury and public vote.
Credit: Ryan Postel, Fermilab
This year’s Global Physics Photowalk has 16 participating particle physics laboratories from three continents. The winning photos will be featured in a future issue of the CERN Courier and in Symmetry magazine.
“Enabling photographers to capture the research and technologies at Fermilab is another way for people from all over the world to see the amazing high-energy particle physics we do,” said Fermilab’s interim director, Young-Kee Kim. “The connection between art and science is profound and can be universally understood in any language.”
Photos from previous years can be viewed on the Interactions website. Photographers of all skill levels are welcome and do not need to be a U.S. citizen to apply.
Space is limited for the Fermilab Photowalk day scheduled for Saturday, July 26, 2025, from 8 a.m. to 12 p.m. Participants must submit the online application by June 1, 2025.
The 2025 Global Photowalk is organized by the Interactions Collaboration, an international group of science communicators dedicated to telling stories about particle physics research and achievements.
You can follow the Photowalk on social media using #PhysPics25.
Fermi National Accelerator Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.
A team of researchers from the U.S. Department of Energy’s Fermi National Accelerator Laboratory, Caltech, NASA’s Jet Propulsion Laboratory, University of Geneva and Federico Santa María Technical University in Chile recently tested a new technology to determine whether superconducting microwire single photon detectors, or SMSPDs, are feasible for use in future particle physics experiments. The results found that the SMSPDs were able to detect a variety of particles with impressive detection efficiency, making them a promising technology to advance particle physics research and dark matter detection. This achievement represents a significant step toward developing advanced detectors for next-generation particle physics experiments.
The groundbreaking study was conducted at Fermilab, where an array of SMSPDs was used to measure particle efficiency and time resolution while detecting high-energy particles such as protons, electrons and pions. Efficient and accurate detection these particles is essential to enhancing scientists’ understanding of fundamental physics.
“We are very excited to work on cutting-edge detector R&D like SMSPDs because they may play a vital role in capstone projects in the field such as the planned Future Circular Collider or an International Muon Collider,” said Fermilab scientist Cristián Peña, who led the research. “And we are thrilled to have assembled a world-class team across several institutions to push this emerging research to the next level.”
Traditional particle detectors, while effective, often face limitations in sensitivity, spatial resolution and time resolution — critical requirements for accurately detecting particles. The need for ever more precise particle detectors has driven researchers to explore new sensing materials and technologies.
The SMPSD arrays, which were designed and fabricated at Jet Propulsion Laboratory, or JPL, are a variation of high-performing superconducting nanowire single photon detectors, or SNSPDs. Both devices work similarly. A thin film of superconducting material — in this case, 3-nanometer-thick tungsten silicide — is patterned into 1.5-micron-wide wires covering an active area that detects charged particles as they deposit energy into the sensor. Researchers apply a bias current just below the maximum current the superconducting wire can sustain. Once the charged particles deposit enough energy to break the superconductivity, the bias current diverts from the wire to produce a detectable electrical pulse.
SNSPDs have been instrumental in fields like quantum information science and space exploration due to their ultra-low energy thresholds and exceptional time resolution. For example, JPL develops them for space-based optical communications, while Fermilab uses them in its quantum networks, dark matter research and astrophysics applications. However, for particle physics, their use has been limited because of their small active detection area and little to no particle beam studies.
In contrast, SMSPDs have a much larger active detection area than their nanowire cousins, marking a significant step forward for the large particle detectors needed for particle physics experiments.
The researchers reported a consistent detection efficiency using the SMSPDs across different detection areas and bias currents. A silicon tracking telescope installed at Fermilab’s Test Beam Facility provided the precise and crucial spatial resolution needed to accurately measure detection efficiency. In addition, the timing resolution, which is essential to accurately track particles in next-generation accelerator-based experiments, was measured for the first time for such charged particles.
“This is significant step toward developing advanced detectors for future particle physics experiments,” said coauthor Si Xie, a scientist at Fermilab with a joint appointment at Caltech as a research scientist. “This is just the beginning. We have the potential to detect particles lower in mass than we could before, as well as exotic particles like those that may constitute dark matter.”
The research team is already working to further improve SMSPD arrays and other similar technologies.
“We are in the process of optimizing SMSPD arrays for high-energy particle detection in terms of time resolution and detection efficiency so this technology can be used in next-generation accelerator-based experiments,” said Christina Wang, a Lederman Fellow at Fermilab who is also a co-author on this study. “We will continue to test these optimized arrays with greater precision.”
“In future experiments, the team plans to explore using SMSPD arrays in accelerator-based experiments by characterizing their ability to operate effectively in high-radiation environments with high-particle occupancy,” added Wang.
These are crucial steps toward integrating this promising technology into tomorrow’s particle detectors to help discover new physics phenomena.
The study in the Journal of Instrumentation is titled “High energy particle detection with large area superconducting microwire array” and was funded by the U.S Department of Energy, Fermi National Accelerator Laboratory, the National Agency for Research and Development (ANID) in Chile and the Federico Santa María Technical University.
Fermi National Accelerator Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.