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December 14, 2021 03:30 am

Researchers Are Hoping To 'Hear' Dark Matter Using a Super-Cooled Experiment

An anonymous reader shares an excerpt from a report by Gizmodo, written by Isaac Schultz: The Dark Matter Radio project is attempting to detect hidden photons in a specific frequency range by methodically turning the dial, in what amounts to a patient, sweeping search of the wavelengths where such a particle could sound off. Later generations of the radio will hunt axions. [...] The current Dark Matter Radio experiment is the prototype, or Pathfinder, for larger projects down the line. It consists of a liter-volume cylinder made of superconducting niobium metal, around which is tightly wound niobium wire. It looks a bit like someone wound guitar string on a spool's vertical axis instead of its horizontal axis. That's the Pathfinder's inductor. If a hidden photon resonating at the frequency the Pathfinder was tuned to passed through it, the change in magnetic field would induce a voltage around the contraption's inductor. "The null hypothesis is that there shouldn't be any radio waves inside of that box unless, in this case, hidden photons, which are our particular flavor of dark matter," said Stephen Kuenstner, a physicist at Stanford University and a member of the DM Radio team. Hidden photons "can pass through the box and they have some probability of interacting with the circuit in the same way that a radio wave would," Kuenstner said. To amplify any signal the Pathfinder picks up, there's a hexagonal shield of niobium plates sheathing the aforesaid components that acts as a capacitor. That amplified signal is then transported to a quantum sensor called a SQUID (a Superconducting QUantum Interference Device), a technology invented by the Ford Motor Company in the 1960s. The SQUID lives on the bottom of the radio and measures and records any signals picked up. The smaller the expected mass for the axion becomes, the more elusive the particle is, as its interactions with ordinary matter are proportional to its mass. So it's important that the next generation of DM Radio becomes more sensitive. The way the experiment is set up, "the frequency on the dial is the mass of the axion," [said Kent Irwin, a physicist at Stanford University and SLAC and the principal investigator of Dark Matter Radio]. Convenient! The mass of these particles doesn't even compare to the smallest things you might think of, like atoms or quarks. These particles would be somewhere between a trillionth and a millionth of an electronvolt, and an electronvolt is about a billionth of a proton's mass. The helium Pathfinder uses is gaseous, and remains a relatively warm 4 kelvin (in other words, four degrees above absolute zero), but the next experiment -- Dark Matter Radio 50L -- will use liquified helium, cooled to less than one degree above absolute zero. All the better for hearing dark matter with. DM Radio 50L sits in the corner of a large room in the Hansen Experimental Physics Lab at Stanford. The room looks a little bit like the TV room in Willy Wonka's factory; it has high ceilings, lots of inscrutable equipment, and is glaringly white. Two 6-foot-tall dilution refrigerators on one side, abutting a deep closet, are the radio. The two machines are fed gaseous helium sitting in tanks in the next room, which they then cool down into liquid helium of a frigid 2 kelvin. Magnets inside gold-plated copper and aluminum sheathes will do the job of converting any detected axions into radio waves for physicists to interpret. "The particle physics community is -- the analogy is often said -- just like a battleship. It takes a while to turn and it has a lot of momentum," Irwin said. "So even though I think that there's a lot of reasons to believe that these radio-like dark matter signals are more attractive -- the axionic signals -- than [Weakly Interactinv Massive Particles (WIMPs)], there's still a lot of giant experiments searching for little things, which is good." The team behind the Dark Matter Radio is "currently working with the Department of Energy on a next-next-generation experiment that will look for axions in a cubic meter, hence its name of DM Radio-m3," adds Gizmodo. "In the more distant future, Irwin and his team have aspirations for a project called DM Radio-GUT, which would be closer to the scale of some of the largest physics experiments on the planet." "All told, Irwin said, the favored area for axion mass could be searched in the next couple of decades using larger experiments -- though the team could simply find an axion before then, potentially ending the hunt for dark matter in its entirety. With enough listening, we might have an entirely new particle for the textbooks. Or maybe there'll be radio silence."

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