For many years, individuals have been attempting to directly identify dark matter: the elusive mass in our universe. Currently, findings from the FAMU-FSU College of Engineering are paving the way for a novel, highly-sensitive detector — and although it’s still undergoing research and development, it has already managed to search for types of dark matter that other detectors have been unable to identify.

Traditionally, most dark matter investigations have focused on two categories of dark matter: ultra-light axions and more substantial WIMPs (weakly interacting massive particles). However, the new TESSERACT experiment, which stands for Transition-Edge Sensors with Sub-EV Resolution And Cryogenic Targets, explores the intermediate regions, searching for low-mass dark matter approximately a hundred to a thousand times lighter than a WIMP.

“It’s a type of Goldilocks dark matter,” stated Dan McKinsey, the project director for TESSERACT and a researcher at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), which is overseeing the experiment. “There’s this untested area that presents an opportunity for discovery. Our detector possesses the sensitivity, even in this preliminary stage, that enables us to search for dark matter candidates that no one has been able to explore previously.”

In a paper uploaded to the online archive arXiv, TESSERACT researchers disclosed their initial dark matter findings, revealing no signs of low-mass dark matter between masses of 44 MeV/c2 and 87 MeV/c2 (where MeV denotes millions of electronvolts). By comparison, the mass of a proton is slightly under 1,000 MeV/c2, and the most recent findings from LZ, the world’s premier WIMP experiment, searched for dark matter down to 9,000 MeV/c2. This represents the first instance where any experiment has searched for nuclear recoil signals from dark matter with mass under 87 MeV/c2.

If researchers were to uncover dark matter in this new domain, they would require a new explanation for its interactions. For instance, while WIMPs interact through the weak force, low-mass dark matter might suggest the presence of an unknown fifth fundamental force.

While numerous advanced dark matter experiments utilize vast quantities of detector material or enormous magnets, TESSERACT’s strength lies not in its dimension but in its sensitivity. These pioneering world-class results stemmed from meticulously designed and shielded silicon chips that are one square centimeter, about a quarter of the size of a postcard stamp. These detectors were developed at UC Berkeley and manufactured at Texas A&M University.

TESSERACT employs transition-edge sensors, a form of superconducting detector, that function at around 8 millikelvin (close to negative 460 degrees Fahrenheit). Even the slightest amount of heat — for instance, from a lightweight dark matter particle colliding with the chip and transferring some energy — can trigger the sensor.

A significant portion of the work involved in designing the specialized cryostat utilized for these dark matter explorations was spearheaded by TESSERACT collaboration executive committee member Wei Guo in his cryogenics laboratory at the Florida State University-based National High Magnetic Field Laboratory. Guo, an educator at the FAMU-FSU College of Engineering, is acclaimed for his contributions to quantum engineering, cryogenic heat and mass transfer, and the investigation of quantum fluid dynamics in superfluid helium-4.

“I am proud of the significant contributions our cryogenics lab has made to the Dark Matter search initiatives of the TESSERACT collaboration,” Guo remarked. “Under the leadership of Dr. Yinghe Qi, we have achieved remarkable advancements in crafting a specialized cryogenic system that guarantees outstanding radioactive background protection while ensuring stable sensor cooling below 10 mK.”

Researchers have been involved in R&D since 2020 to enhance sensitivity and mitigate (or account for) potential sources of noise that could obscure a dark matter signal. This includes discovering the optimal recipe for crafting the sensors and minimizing background vibrations and electromagnetic interference in the dilution refrigerator that contains the silicon chip. The compact size of the detector is also advantageous; less area implies fewer background interactions.

“We’ve been striving to make the sensors very consistent and of high fidelity at extremely low temperatures,” stated Vetri Velan, a Chamberlain Fellow at Berkeley Lab and co-lead of the analysis. “The lower the transition temperature of the sensor, the superior the noise performance and the enhanced sensitivity to dark matter. So, it’s all about maximizing the sensitivity of these sensors.”

TESSERACT addresses a common challenge faced by sensitive detectors: a persistent but unexplained source of excess noise at low energies, the very region where dark matter may exist. The experiment’s methodology in manufacturing and shielding the detectors has diminished that background rate by a factor of 30.

“The instruments we are operating are remarkably quieter compared to virtually any other device that has been used,” remarked Michael Williams, a Chamberlain Fellow at Berkeley Lab and co-lead of the analysis. “Additionally, there’s a substantial overlap between the work we’re conducting on these devices and other quantum material sciences. As we enhance these transition-edge sensors for our objectives, we can also adopt the same engineering to create better qubits and quantum computers.”

An INITIATIVE DESIGNED TO ALTER
Most dark matter investigations are conducted deep underground, utilizing thousands of feet of rock to assist in blocking particles from space that might interact within the detector. With this initial detector prototype, TESSERACT has thus far explored new territories for dark matter from what is effectively Earth’s surface: the sub-basement of UC Berkeley’s Birge Hall (not far from the location of John Clauser’s Nobel Prize-winning experiment on photon entanglement that established the foundation for our current quantum transformation).

However, to further enhance the detectors’ sensitivity, researchers

Aiming to establish the complete experiment beneath 1,700 meters (5,600 feet) of rock in Europe’s most profound underground facility: France’s Modane Underground Laboratory. Construction is anticipated to commence in 2025, with the experiment expected to initiate by 2029, searching for dark matter with masses as low as 10 MeV/c2. The experiment will expand from its existing size, approximately akin to a phone booth, to a six-foot cube.

The core of TESSERACT lies within its transition-edge sensors, while researchers are simultaneously developing supplementary detector modules to enhance their chances of identifying dark matter. HeRALD (Helium Roton Apparatus for Light Dark matter) represents the inaugural instance of a dark matter experiment utilizing superfluid helium and will employ TESSERACT’s silicon chips as the sensor components of the detector. SPICE (Sub-ev Polar Interactions Cryogenic Experiment) will utilize individual sapphire and gallium arsenide crystals. Furthermore, the scientific teams in France will contribute a sensor composed of silicon and germanium. These various modules will provide researchers distinctive methods to search for dark matter and test a range of theories. Both initiatives will leverage the same cryostat system, developed under the guidance of Guo’s team.

The protective enclosure encircling the experiment is engineered to disassemble, allowing researchers to readily access TESSERACT’s components and replace them within a few days. Should HeRALD detect compelling evidence of dark matter, scientists can substitute in SPICE to verify the outcome (or vice versa). In contrast, numerous sophisticated dark matter experiments are constructed like a ship in a bottle; it could require months or years to dismantle and replace components, if feasible at all.

Researchers are currently advancing both HeRALD and SPICE and exploring new manufacturing techniques to further enhance the transition-edge sensors.

Enhanced detectors and an underground setting will enable the experiment to probe for lower mass particles and boost the likelihood of observing exceedingly rare dark matter interactions with ordinary matter.

“This finding is the initial sign that we can explore this new realm of low-mass dark matter through experimental examination,” McKinsey remarked. “It’s incredibly exciting to have a small experiment operating in the basement that can evaluate new concepts regarding dark matter. This is merely the opening barrage for TESSERACT. We anticipate numerous additional discoveries over the forthcoming decade.

The TESSERACT collaboration also comprises researchers from Argonne National Laboratory, Caltech, IJCLab (Laboratoire de Physique des 2 Infinis Iréne Joliot-Curie), IP2I (Institut de Physique des 2 Infinis de Lyon), LPSC (Laboratoire de Physique Subatomique et de Cosmologie), Texas A&M University, UC Berkeley, the University of Massachusetts Amherst, the University of Zürich, and QUP (the International Center for Quantum-field Measurement Systems for Studies of the Universe and Particles).

The Department of Energy’s Office of Science is the foremost supporter of fundamental research in the physical sciences in the United States and is dedicated to addressing some of the most urgent challenges of our era. For further information, please visit energy.gov/science.

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