June 23, 2025
UChicago physicist Karri DiPetrillo’s mission to bring a muon collider to fruition
Particle colliders are the only laboratory setting where scientists can recreate the conditions of the early universe. In 2012, physicists discovered the Higgs boson using the proton-accelerating Large Hadron Collider (LHC), currently the world’s highest-energy collider. This groundbreaking discovery opened the door to studying how fundamental particles first gained mass.
Many physicists believe that a collider with ten times the energy of the LHC is the next step in exploring the universe’s history and secrets. A particle collider operating at the 10 TeV scale, such as a muon collider, is essential for unraveling the mysteries surrounding the nature of the Higgs boson, its connections to phase transitions in the early universe, and the properties of dark matter. A team that includes UChicago physicist Karri DiPetrillo is working to turn the dream of a muon collider into a reality.
Next-generation particle collider
A muon is an elementary subatomic particle roughly 200 times heavier than an electron. Hypothetically, a muon collider would smash muons into their antiparticles in two giant particle detectors, creating massive new particles. Compared to an equally powerful proton collider, a muon collider could be less expensive, more power-efficient, and more compact—small enough to be housed at Fermi National Accelerator Laboratory.
However, a muon is extremely short-lived—it exists on average for only 2.2 microseconds before decaying into an electron and two types of neutrinos. Physicists would need to produce, accelerate, and collide muons before they decay. Because muons are unstable, no one knows if a muon collider is possible. Considerable research is necessary to address the unique challenges of developing such a high-energy collider.
The United States pursued muon collider research and development in the early 2010s through the US Muon Accelerator Program until the 2014 Particle Physics Project Prioritization Panel (P5) recommended cutting all funding. Despite promising designs and simulations, “there wasn’t enough enthusiasm from the physics community,” said DiPetrillo, Assistant Professor of Physics who spends most of her time working on the ATLAS experiment at the LHC.
Yet, over the past decade, significant advancements in proton sources, high-power targets, high-field magnets, and ionization cooling have brought the prospect of a muon collider closer to fruition, fueling enthusiasm. “As part of long-term planning processes in Europe and the US, physicists solidified the case for a 10 TeV muon collider,” said DiPetrillo, “and accelerator experts determined there were no technological showstoppers.”
Earlier this month, the National Academies of Sciences, Engineering, and Medicine released a new report that lays out a 40-year vision for particle physics; its top recommendation calls for the United States to build a muon collider.
The LHC’s larger and higher-energy proton-colliding successor may not be built for another 50 years, but a muon collider could potentially be realized within two decades. “Colliders are monumental endeavors,” said DiPetrillo. “If we want to see that breakthrough in a reasonable timescale, dedicated R&D needs to begin now.”
Background research
In May, the Simons Foundation announced an award supporting research aimed at muon collider development, granted to DiPetrillo; Isobel Ojalvo, an Assistant Professor at Princeton University; and Tova Holmes, an Assistant Professor at the University of Tennessee, Knoxville. The project seeks to advance a muon collider’s experimental design while fostering interdisciplinary collaboration between accelerator physicists and collider experimentalists. The team’s efforts will concentrate on improving beam-induced background simulations and developing AI-driven techniques to distinguish rare events from the background.
Approximately 10 million muons decay in each particle collision event, generating a stream of high-energy electrons and neutrinos that can interfere with the detector’s ability to measure the particles produced by the collision. Separating this background noise (beam-induced background) from collision data poses challenges for detector design.
DiPetrillo’s team will address the computational challenge of simulating this exceedingly high number of decay particles as well as developing algorithms to mitigate the impact of that beam-induced background on detector performance. “To extract the physics we’re after, these algorithms must sit directly in our detector readout electronics,” said DiPetrillo. “We will concentrate on developing machine learning algorithms that can be implemented in custom microelectronics.”
The project will also address key aspects of accelerator design. The acceleration process starts by hitting a target with a high-power proton beam. This produces subatomic particles called pions, which decay into a basketball-sized cloud of muons that must be compressed—or cooled—into a tight bunch about 25 microns wide before the muons can be accelerated. “The number of muons that survive the process and the size of the bunch have a direct impact on the number of resulting collisions and science output of the experiment,” explained DiPetrillo. “Our team will focus on the muon production point and cooling muons into small bunches.”
About the award
The award, “Muon Colliders: A new direction in High Energy Physics,” is part of the Simons Foundation’s targeted grants in the Math and Physical Sciences, intended to “support high-risk theoretical mathematics, physics and computer science projects of exceptional promise and scientific importance.” It will support three PIs, three postdoctoral researchers, and three students for two years.
In the US, funding to support rigorous muon collider R&D is sparse. “Experimentalists and accelerator physicists have largely been working on this in our free time. Having the support for full-time personnel will enable us to make breakthroughs in terms of addressing design and computational challenges,” said DiPetrillo.
“There has been a lot of talk about enabling a new generation of physicists to realize a future collider,” she added. “It’s wonderful that the Simons Foundation supported this group of PIs. We’re three women (still rare in physics), all early career faculty, and have played a leading role in enabling muon collider progress over the past few years.”
DiPetrillo is too early in her career to have designed the detectors and colliders that will define most of her academic research. She is eager to lead the field toward innovative new collider technology. “I find the design and technology challenges on both the accelerator and detector sides fascinating and full of opportunities for creativity,” said DiPetrillo. “I’m also excited about the potential to have a collider just an hour away from UChicago.”