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When researchers examine the universe, they observe stars swirling around their galaxies at speeds that defy the established laws of physics, alongside clusters of galaxies pulling each other with excessive force. They postulate that something must be generating more gravitational pull than all currently visible matter can elucidate — but regardless of what this substance may be, it remains undetectable. Dark matter is essentially a placeholder: A well-documented gap in our comprehension of the cosmos.

Scientists have proposed various hypotheses to elucidate what dark matter could be, but thus far, no investigation has yielded convincing proof to validate any of them. A collaborative team of global physicists is presently developing a new variety of dark matter detector with the objective of achieving the first direct sighting of this enigmatic material. Data from the detector’s prototype has already dismissed one of the predominant theories of dark matter’s origin.

The recent study was published on August 13 in Physical Review Letters.

“DAMIC-M may offer our best opportunity to resolve the dark matter puzzle in the years ahead,” stated Alvaro Chavarria, an associate professor of physics at the University of Washington and the lead researcher for the DAMIC-M (DArk Matter In CCDs at Modane) international consortium responsible for this research.

Most physicists believe that dark matter consists of particles, akin to all other matter in the cosmos. For reasons yet to be understood, this category of particles does not engage significantly with standard matter or photons. However, it could interact just enough to be detected by a highly sensitive device as dark matter particles traverse the Earth.

“We are aware of the quantity of dark matter present in the universe, but we remain uncertain if it comprises numerous light particles or a smaller number of heavier ones,” Chavarria remarked. “Our goal is to rule out all conceivable theories until we uncover something.”

For years, the prominent candidate for dark matter was a hefty theoretical particle humorously dubbed the WIMP, or Weakly Interacting Massive Particle. However, experiments have not identified a single WIMP, leading many researchers to redirect their inquiries toward lighter alternatives called “hidden-sector” particles. Lighter particles would make detection more challenging, so to respond to this issue, Chavarria and the DAMIC-M team devised a new category of detector.

The innovative device functions somewhat like a digital camera, employing a silicon sensor known as a CCD, containing millions of pixels. The sensor identifies photons and converts them into an image. This dark matter detector is composed of similar — albeit much more sensitive — CCDs capable of capturing minute and rare particle interactions.

Chavarria and his team assembled and evaluated the CCD modules in their UW clean room laboratory. They subsequently transported the apparatus directly to the Laboratoire Souterrain de Modane, a facility situated beneath 5,000 feet of rock within the French Alps. There, it was encased in lead to shield it from radioactive materials in the surrounding rock and commenced operation. All of these steps were taken to ensure the experiment was conducted with pristine equipment.

“We are searching for exceedingly rare signals in the detector — perhaps on the scale of one signal per year,” Chavarria explained. “It is essential to eliminate all forms of interference from other types of radiation.”

Despite the sophistication of the instrument, it remains a prototype. The DAMIC-M team is currently constructing a significantly larger and more sensitive detector, projected to be operational by early next year. Nevertheless, the prototype has proven to be beneficial. Over two and a half months, it captured several thousand “images,” which the team combed through for signs of dark matter interactions. None were found.

However, in the realm of dark matter detection, the lack of findings is a finding in and of itself.

Historically, scientists have considered two potential scenarios regarding how hidden-sector particles could have emerged in the early universe. Each scenario posits a different prediction regarding how these particles may appear today. Should the hidden-sector theory hold true, one of those two scenarios should be valid. The “null” outcome by the DAMIC-M prototype significantly diminishes the likelihood of one of the scenarios — and the full-scale detector is sensitive enough to finalize the inquiry. Either the new detector will uncover dark matter, Chavarria stated, or it will be necessary to explore new theories.

“If DAMIC-M fails to yield results, I doubt we will be hearing about hidden-sector models of dark matter any longer.”

Other possibilities remain. It could be that hidden-sector particles exist, but only account for a minor fraction of all the dark matter in the universe. Tiny particles known as axions might also be part of the equation — they are the focus of another detector located at the UW. In other words, dark matter might consist of another particle — or multiple particles.

However, with DAMIC-M, researchers can refine the number of prevailing theories to those deserving further exploration, all while advancing the technology required to do so.

“We have been dedicated to this since I arrived at the UW in 2018,” Chavarria stated. “The development of the module alone…

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It required nearly five years of effort here on campus. Now, owing to the impressive outcome from the prototype, we are quite assured that the full-scale detector will function effectively. I’m extremely thrilled. This was my aspiration.

Co-authors encompass Heng Lin, a prior UW postdoctoral researcher who currently serves as a postdoctoral fellow at Johns Hopkins University; Kellie McGuire, who undertook this investigation as a graduate student at UW; Michelangelo Traina, a former UW postdoctoral researcher who is presently a postdoctoral fellow at the Instituto de Física de Cantabria in Spain, and Kush Aggarwal, a UW graduate student. A comprehensive list of co-authors is available with the publication.

This investigation received funding from the European Research Council; the National Science Foundation; The Kavli Foundation; The Ministry of Science and Innovation in Spain; the Swiss National Science Foundation; and the Centre National de la Recherche Scientifique (CNRS).

For additional details, reach out to Chavarria at [email protected].

This narrative was modified from a news release by the University of Chicago.

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