When Steven Gardiner first embarked on his scientific career, his research centered on the practical applications of nuclear physics, such as prototyping neutron detectors for counterterrorism and improving simulations used by nuclear engineers to design reactors. Fundamental research on neutrino physics was far from his mind until he considered PhD programs and heard about the Deep Underground Neutrino Experiment, hosted by the U.S. Department of Energy’s Fermi National Accelerator Laboratory.
After speaking to his adviser, Bob Svoboda at University of California, Davis, about the exciting science potential of DUNE, Gardiner recalled, “I became a neutrino person and never looked back.” He joined Fermilab in 2018, bringing a unique background in neutron simulations to the study of some of the most elusive particles in the universe.
This career track recently earned Gardiner a Department of Energy Early Career Award, which provides funding to explore the low-energy research potential of DUNE. While the experiment is primarily designed for high-energy beam physics, Gardiner is advocating for its use as an unusual kind of telescope. Rather than collecting rays of light to study the universe, DUNE will be sensitive to ghostly low-energy neutrinos coming from outer space, including those from the Sun, supernovae, black holes and possibly dark matter.
“Even though DUNE is designed for beam physics, you can go way lower in energy, and it still performs,” Gardiner said. He believes his specific background allows him to make a “unique contribution due to my career trajectory,” taking him from neutrons to neutrinos.
The technical heart of this research involves upgrading a computer simulation code called MARLEY, or Model of Argon Reaction Low Energy Yields. Because neutrinos interact so weakly with ordinary matter, they are not directly visible in detectors. Instead, physicists must look for extremely rare collisions between neutrinos and atomic nuclei. Like a subatomic version of a car crash investigation, the tracks left by particles coming out of each collision provide clues about what originally happened. To put these puzzle pieces back together, scientists rely on detailed simulations of the collision physics, which is where MARLEY becomes essential. Results from these simulations will help researchers tell the difference between uninteresting noise, low-energy cosmic neutrinos and potential signals from undiscovered new particles. The ultimate goal of this work is to push the boundaries of physics. “My hope is that as a result of this project, we are thinking about new physics beyond the Standard Model,” Gardiner said.
He also emphasized science opportunities going far beyond the microscopic world. “Neutrinos reveal the inner workings of stars to us, whether it’s the core of our own Sun or the first moments of a supernova explosion,” Gardiner said. By refining the models used to interpret neutrino interactions, he is helping to open a wider view of the distant universe. “DUNE is a new window to the cosmos,” he said. “It gives us a new way of seeing into a hidden world where all kinds of crazy stuff might be going on.”
The DOE funding ensures that low-energy neutrino research may expand our understanding of the fundamental building blocks of the universe through the unparalleled sensitivity of the DUNE detectors.
Fermi National Accelerator Laboratory is America’s 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.
For nearly a century, scientists have been searching for evidence of dark matter, an invisible substance they believe makes up most of the mass of the universe. Such a discovery could lead to a greater understanding of our universe and how it works.
But finding this elusive material is easier said than done. For one thing, nobody knows exactly what dark matter is made of, so the range of particle masses and their signal frequencies is incredibly broad. Also, dark matter interacts infrequently with ordinary matter and light. To observe it, scientists rely on extremely sensitive detectors to capture very weak signals produced by dark matter particles.
In a study published in Physical Review Letters, scientists at Fermi National Accelerator Laboratory, University of Chicago, Stanford University and New York University used a state-of-the-art detector to speed up the search for one theorized dark matter particle — the dark photon — with unprecedented precision. If it exists, the dark photon would be distantly related to the photon, a visible particle of light.
Their research is enabled by the U.S. Department of Energy’s Quantum Information Science Enabled Discovery program, which partners Fermilab and university scientists to advance quantum sensor development for future high-energy physics experiments.
“Fermilab’s longstanding expertise in designing and building ultrasensitive, low-noise electronics makes it the ideal place to further this technology for next-generation quantum science research like dark matter searches,” said Aaron Chou, a scientist at Fermilab who worked on the study.
The dark photon resides in a narrow frequency band, which means to see its signal a radio-like detector must be carefully tuned to its exact frequency. Scientists developed this detector to be capable of capturing weak signals from dark photons by placing an electrically-tunable instrument called a superconducting quantum interference device — or SQUID — inside a three-dimensional microwave cavity. The device’s superconductance means it has no resistance to energy and can therefore pick up even the faintest signals, such as those from a dark photon.
Key to the detector’s ability to speed up the search for a tiny signal in a broad range of frequencies is flux tuning, which uses electricity to tune the device instead of manually.
“Rather than physically turning a dial to a specific frequency like with a radio, we apply electromagnetic flux to the SQUID, precisely controlling its ability to oppose changes in electricity flowing through it,” said Fang Zhao, a former Fermilab postdoctoral researcher who led the study.
Somewhat like an electronic pendulum, this flux essentially changes how quickly or slowly the device moves. The microwave cavity is coupled to the SQUID, so changes in the SQUID correspondingly changes the speed of the cavity, allowing it to “listen to” different frequencies.
“Without the ability to electrically tune its frequency, you would have to build billions of detectors to capture the signal,” said Ziqian Li, a former University of Chicago graduate student who also worked on the study. “In contrast, we can build a few flux-tunable detectors and place them at various frequencies, enabling capture of possible signals much faster than before.”
Conventional tunable detectors require mechanically changing the shape of a cavity by physically exerting force or adding mechanical parts inside connected circuits. This poses a challenge because qubit-based detectors require ultracold temperatures to function properly, and extreme cold can cause these parts to seize and break. In addition, mechanical parts emit a lot of heat, which creates noise in the cavity, obscuring signals and decreasing the ability to read and understand the quantum information stored inside the detector.
But use of flux tuning not only enables rapid frequency scanning, it also generates very little heat. This overcomes a major challenge for dark matter searches — preserving coherence. Quantum coherence, says Zhao, is what makes these sensors so precise.
“It’s a fundamental requirement for quantum devices to be protected from anything like heat or noise that might obscure such fragile signals and preserve them long enough for us to detect them.”
The scientists scanned a relatively large frequency range of 22-megahertz over three days. During this time, they were able to speed up the scanning rate by at least a factor of 20 over mechanical tuning methods. While their search did not turn up any dark photons, they were able to build on previous studies at multiple institutions and narrow the frequency range where dark matter can exist.
“What we’re really trying to do is to build a detector that is more sensitive than anybody else has ever made before; we did that,” said Chou. “We also showed that the detector was compatible with the qubit-based signal readout that we use for dark matter searches and that everything was integrated and everything just worked. It laid the foundation for larger dark matter searches.”
The current detector is very simple, with one cavity and one tunable device — the SQUID. However, work is underway to scale up this technology. Researchers could combine 10, 50 or even more cavities, each covering a different frequency range, with a single tunable element and simultaneously scan a 50 times wider range.
“While there is more work to do to improve scaling, we know now we can use the same detection technique to allow us to detect a large range of the dark photon within a few days, and then the full coverage search of the dark photon is within our reach,” said Li.
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.
Aleksandra Ćiprijanović, a Wilson Fellow and associate scientist at the U.S. Department of Energy’s Fermi National Accelerator Laboratory, is a recipient of a 2025 DOE Early Career Award. Her project, “Bridging the Gap Between Scientific Datasets with Artificial Intelligence,” was selected for funding by the Office of High Energy Physics as part of the new Computational Research in High Energy Physics program.
Ćiprijanović’s project aims to address a problem that she encountered almost a decade ago when she first started dabbling with AI in her research: the domain shift problem. The problem occurs when a machine learning model is trained on one dataset but is tested or deployed on data that comes from somewhere else; since the model only learned patterns from the training data, its performance often drops when the data changes.
The domain shift problem is persistent in high-energy physics research. Scientists often use simulations to train their AI models, but computational constraints, approximations and unknown physics create unavoidable differences between simulations and real data. This means simulation-trained AI models may perform poorly when they are applied to experimental data.
“Trying to solve this would help the high-energy physics community in general,” said Ćiprijanović.
So Ćiprijanović wants to create a universal AI analysis framework to bridge the gap between simulated and real data. “The main deliverable of this project is going to be a software package that is general and broad and easy to use for all communities,” she said. “You can just plug in your own dataset, easily choose the type of AI model that you want to train and a downstream task that you want to solve.”
While she plans to start with cosmological data — since that is her scientific home — Ćiprijanović also intends to test her project on collider and neutrino physics.
“I really do want to make a software framework that will be used across different high-energy physics frontiers,” she said.
The framework will have a modular structure and a number of data, model and task options to enable broad scientific use and solutions to any high-energy physics domain-shift problem.
Fermilab is uniquely positioned to support this project, said Ćiprijanović. The lab’s science and computing capabilities will enable the creation of a universal AI analysis framework that will work with a vast range of high-energy physics research needs and coding standards.
“We will need to find people to test out the code and give us inputs from cosmic and from neutrinos and from the collider world,” said Ćiprijanović. “Luckily, at Fermilab, we have experts from all these frontiers! Fermilab is the place to do this.”
Since 2010, the highly competitive DOE Office of Science Early Career Research Program has distributed funding annually to support outstanding early career scientists at universities, national laboratories and Office of Science user facilities.
Fermi National Accelerator Laboratory is America’s 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.
What if Olympic officials could record sprinters’ times only to the nearest minute? “We would know who started the race, and who finished the race, but that’s it,” said Bryan Cardwell, a postdoctoral researcher at the University of Virginia. “There’s no way to know who arrived first and who arrived last.”
Cardwell and his colleagues on the CMS experiment are currently tackling a similar problem. The CMS experiment records the tracks and properties of subatomic particles created by the Large Hadron Collider, the world’s most powerful particle accelerator. As it stands, physicists get a picture of all the particles produced in a collision, but they have insufficiently detailed information about when the particles were produced or how fast they were traveling, making it difficult to tell them apart.
That’s why CMS scientists are building a new detector that will let them watch particle collisions as they unfold, with 30-picosecond (0.00000000003 second) accuracy.
“In 30 picoseconds, light moves about one centimeter.”
Chris Neu, University of Virginia
“In 30 picoseconds, light moves about one centimeter,” said Chris Neu, a professor at the University of Virginia. “We’re talking about measuring the time of arrival of very fast objects with a very high precision.”
Some scientists suspect that rare and massive particles that take a long time to decay could move more slowly than lighter, more common particles. This means that when they do finally decay, their “daughter particles” will be a step behind. The difference would be tiny; a photo finish after a race that is only four feet long. But scientists hope that a precise “stopwatch” detector will help them tell the difference.
“We’ll be able to see if any particles are habitually arriving late,” Cardwell said. “That is inherently interesting.”
Turning ripples into tsunamis
The new timing detector consists of two parts: a barrel equipped with roughly 10,000 crystal sensors, and end caps coated with hair-thin silicon wafers. While silicon sensors are common inside CMS, this new detector has a special gain layer that amplifies the signal before it is read out.
“A small signal is like a tiny ripple on the surface of the water, and it gets lost among the little waves around it, so it’s hard to tell exactly when it arrived,” said Artur Apresyan, a researcher at the U.S. Department of Energy’s Fermi National Accelerator Laboratory. “The gain layer turns the small signal into a fast-moving tsunami that stands out clearly from the background, making its arrival time very clear. This amplification feature is not present in other CMS detectors; it’s a new design specifically for timing detectors.”
Currently, scientists at Fermilab are building and testing the sensors and support structures in collaboration with their national and international partners.
“The work on the end cap timing detector at Fermilab has been a unique possibility for many junior researchers to participate in the design and construction of a novel kind of detector,” Apresyan said. “These kinds of opportunities are very rare in such large and advanced experiments, and Fermilab provides an exceptional opportunity to allow newcomers to join and learn cutting-edge detector technologies and their applications.”
Unveiling the dark sector
Once the finished detector is installed inside CMS, scientists hope that it will help them separate fast-moving particles from slow-moving dark matter, a mysterious class of particles that are only visible through their gravitational pull.
Dark matter is as good as discovered in the sense that we know it’s there.”
Tevong You, King’s College London
“Dark matter is as good as discovered in the sense that we know it’s there,” said Tevong You, a theorist at King’s College London. “The problem is that none of the Standard Model particles that we know of can account for the properties of dark matter.”
According to You, many theoretical models predict that — in addition to the stable dark matter particles — there could be an entire universe of dark sector particles that might have properties similar to the known particles of the Standard Model.
“Dark matter is very stable, but we also know that stable particles like protons are just a small subset of all visible particles,” You said. “Maybe dark matter is just one small part of an extended dark sector that is full of long-lived particles that can decay into visible matter.”
According to Cardwell, the LHC could be producing dark matter. These dark matter particles would eat up a lot of kinetic energy from the proton-proton collisions and turn it into mass via Einstein’s equation, E = mc2. “This means they have less energy to go fast,” Cardwell said.
When these dark matter particles decay into visible matter, the resulting daughter particles would be lagging behind everything else produced during the collision. This is where the timing detector comes into play.
“If we can measure the time those particles are arriving, we can figure out if they came from a particle that moved a little slower before decaying,” Cardwell said.
Pinpointing exceptional events
The new timing detector will also give scientists a much clearer view of what exactly is happening when bunches of protons collide inside the LHC.
“Right now in CMS, we send something like 100 billion protons through 100 billion protons 40 million times a second,” Cardwell said.
Every time two bunches of protons cross, about 70 collide. Currently, scientists use the spatial coordinates of the smaller particles produced by the collisions to connect the dots and figure out which particles came from what collisions. But spatial orientation alone won’t be enough when scientists turn on the High-Luminosity LHC, which will increase the collision rate by up to a factor of five.
“When there are so many collisions, many of them will literally be at the same point in space,” Cardwell said. “But the collisions don’t all happen at the same time; they’re actually spread out over around 200 picoseconds. With a really, really precise timing detector, 200 picoseconds can suddenly become a very long time; I can slice that 200 picoseconds into a bunch of individual frames.”
These frames will allow scientists to disentangle the messy LHC collisions and pinpoint rare and exceptional events.
“The cool thing about this detector is that it will make everything CMS does better,” Cardwell said. “If we are searching for dark matter, if we are measuring the properties of the Higgs boson, if we’re doing anything at all, the quality of every measurement will increase.”
As a theorist, You is excited about this new timing detector because it will open new avenues for research.
“The best bet for a spectacular discovery at the LHC is through developing new types of searches and new ways of sifting through the data,” You said.
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.