TESSERACT has developed exquisitely sensitive transition-edge sensors that open up new searches for and have potential applications in .
For decades, people have been trying to directly detect : the missing mass in our universe. Now, a new, super-sensitive detector, developed by a collaboration of researchers across the U.S. Department of Energy’s (DOE) national laboratories and partner institutions, is on the case. Even though it’s still in the research and development phase, it’s already been able to search for kinds of that other detectors can’t reach.
Historically, most searches have hunted for two particular kinds of : ultra-light axions and heavier weakly interacting massive particles (WIMPs). But the new (Transition-Edge Sensors with Sub-EV Resolution And Cryogenic Targets) experiment searches in between these regimes, looking for low-mass that’s about a hundred to a thousand times lighter than a WIMP.
“It’s a kind of Goldilocks ,” said Dan McKinsey, the project director for TESSERACT and a researcher at DOE’s Lawrence Berkeley National Laboratory (Berkeley Lab), which leads the experiment. ​“There’s this untested window that gives us an opportunity for discovery. Our detector has the sensitivity, even at this early stage, that allows us to look for candidates no one has been able to look for before.”
“Our team at Argonne has roots in science, and we are very excited about being part of those questions because they are at the heart of what drives us. We’re thrilled by the development of these superconducting technologies, pushing the envelope of what the community does. Every single time it does better, it is world-leading, and that is very exciting.” — Clarence Chang, Argonne physicist
The TESSERACT collaboration also includes researchers at DOE’s Argonne National Laboratory; Caltech; Florida State University; IJCLab (Laboratoire de Physique des 2 Infinis Iréne Joliot-Curie in France); IP2I (Institut de Physique des 2 Infinis de Lyon); LPSC (Laboratoire de Physique Subatomique et de Cosmologie, also in France); Texas A&M University; the University of California, Berkeley (UC Berkeley); the University of Massachusetts Amherst; the University of Zurich; and QUP (the International Center for Quantum-field Measurement Systems for Studies of the Universe and Particles in Japan).
In a paper recently posted to the online repository , TESSERACT researchers presented their first results, finding no evidence of low-mass between masses of 44 MeV/c2 and 87 MeV/c2 (where MeV is millions of electronvolts). For comparison, the mass of a proton is slightly less than 1,000 MeV/c2, and the most , the world’s best WIMP experiment, searched for down to 9,000 MeV/c2. This is the first time any experiment has searched for nuclear recoil signals from with mass below 87 MeV/c2.
If researchers were to find in this new region, they’d need a new explanation for how it interacts. For example, while WIMPs interact through the weak force, low-mass could indicate an undiscovered fifth fundamental force at play.
While many advanced experiments use huge volumes of detector material or giant magnets, TESSERACT’s power comes not from its size but its sensitivity. The new world-leading results came from carefully instrumented and shielded silicon chips that are one square centimeter, roughly a quarter of the size of a postcard stamp. These detectors were designed at UC Berkeley and fabricated at Texas A&M University.
Argonne plays a crucial role in TESSERACT by developing advanced superconducting detectors. Superconductors are materials that can conduct electricity without resistance when cooled below a certain critical temperature. By developing and using materials with very low critical temperatures, it is possible to realize detectors that achieve extremely high sensitivity.
“Our team at Argonne is excited to contribute to the TESSERACT project by leveraging our expertise in superconducting materials,” said Clarence Chang, a researcher at Argonne. ​“We are working on creating sensors with unique materials like iridium coated with platinum, which offer a novel approach to enhancing detector sensitivity. This collaboration allows us to push the boundaries of what is possible in detection.”
TESSERACT uses transition-edge sensors, a type of superconducting detector, that operate at around 8 millikelvin (nearly minus 460 degrees F). Adding even a minuscule amount of heat — say, from a lightweight particle bumping into the chip and depositing some energy — can trip the sensor.
“We’ve been working to make the sensors very consistent and high-fidelity at very low temperatures,” said Vetri Velan, a Chamberlain Fellow at Berkeley Lab and co-lead of the analysis. ​“The lower the transition temperature of the sensor, the better the noise performance and the better the sensitivity to . So it’s all about how sensitive we can make these sensors.”
Researchers have been conducting R&D since 2020 to increase the sensitivity and reduce (or account for) potential sources of noise that might hide a signal. That includes finding the right recipe for manufacturing the sensors and reducing background vibration and electromagnetic interference in the dilution refrigerator that houses the silicon chip. The detector’s small size is also an asset — less area means fewer background interactions.
TESSERACT addresses a problem common to sensitive detectors: a persistent but unexplained source of excess , the same region where might lurk. The experiment’s approach to manufacturing and shielding the detectors has reduced that background rate 30-fold.
“The devices that we are running are so quiet compared to pretty much any other device that’s ever been run,” said Michael Williams, a Chamberlain Fellow at Berkeley Lab and co-lead of the analysis. ​“And there’s a really large overlap between the work we’re doing on these devices and other quantum material science. As we improve these transition-edge sensors for ourselves, we can use the same engineering to make better qubits and quantum computers.”
An experiment designed to change
Most experiments are placed deep underground, using thousands of feet of rock to help block out particles from space that can interact in the detector. With this first detector prototype, TESSERACT has already explored new spaces for from what is essentially Earth’s surface: the sub-basement of UC Berkeley’s Birge Hall (not far from the site of John Clauser’s that set the stage for our current quantum revolution).
But to further improve the detectors’ sensitivity, researchers plan to install the full experiment beneath 5,600 feet of rock in the deepest underground laboratory in Europe: France’s Modane Underground Laboratory. Construction is slated to begin in 2025, with the experiment coming online around 2029 and searching for with masses as low as 10 MeV/c2. The experiment will grow from its current footprint, roughly as big as a phone booth, to a six-foot cube.
The heart of TESSERACT is its transition-edge sensors, but researchers are also developing additional detector modules that improve their odds of spotting . (Helium Roton Apparatus for Light ) will be the first time that a experiment uses superfluid helium and will incorporate TESSERACT’s silicon chips as the detector’s sensors. (Sub-ev Polar Interactions Cryogenic Experiment) will use single crystals of sapphire and gallium arsenide. And the science teams in France will contribute a sensor made of silicon and germanium. The different modules will give researchers unique ways to search for and test different theories.
The shielding that will surround the experiment is designed to come apart, making it possible for researchers to easily access TESSERACT’s components and switch things out in a matter of days. If HeRALD sees intriguing signs of , scientists can swap in SPICE and cross-check the result (or vice versa). In contrast, many advanced experiments are built like a ship in a bottle; it would take months or years to open them up and swap components, if it could be done at all.
Researchers are currently continuing to develop HeRALD and SPICE and test new manufacturing processes to further improve the transition-edge sensors. ​“To get TESSERACT to the sensitivity we want, these detectors have to get even better, even though they’re already the best in the world,” Williams said.
Improved detectors and a subterranean home will let the experiment search for lower mass particles and increase the chance of detecting ultra-rare interactions with regular matter.
“This result is the first indication that we can open up this new regime of low-mass to experimental testing,” McKinsey said. ​“It’s a lot of fun to have a small experiment running in the basement that can test new ideas for . This is really just the opening salvo for TESSERACT. We expect to have many more results over the next decade.”
“Our team at Argonne has roots in science, and we are very excited about being part of those questions because they are at the heart of what drives us,” Chang added. ​“We’re thrilled by the development of these superconducting technologies, pushing the envelope of what the community does. Every single time it does better, it is world-leading, and that is very exciting.”
Chang is also a professor at the University of Chicago. In addition to Chang, Argonne team members include Gensheng Wang and Marharyta Lisovenko.
This project received funding from DOE’s Office of Science High Energy Physics.
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