This dark matter radio can be transformed into new physics

Physicists at Stanford University and SLAC They’ve built a strange instrument they hope will discover dark matter, although which theoretical particles they think they’ll find — hidden photons or tiny blobs called axions — remains a question mark.

Hidden photons are thought to be very similar to ordinary photons, also known as particles of light, except that they have mass and interact Much weaker with ordinary matter, hence their hiding. Axions are a type of subatomic particle (a boson, to be exact) whose existence, if proven, could solve a long-standing problem with the way physicists understand the universe.

Dark matter certainly exists, as its gravitational effects can be seen in almost all galaxies. But while dark matter can be observed indirectly, everything that actually constitutes it, partially or completely, has never been discovered.

Prototype of a dark matter detector.

Radio DM Pathfinder, minus the cylindrical niobium coat.
Photo: Isaac Schultz

A comet in dark matter isn’t necessarily just one thing; There can be multiple reasons why 27% of the universe It appears to be dark matter. Common candidates include weakly interacting massive particles (WIMPs), less massive axons, hidden photons (sometimes called dark), and a class of objects known as Huge built-in aura objects (Macho). WIMPs used to be the pre-filter for dark matter, but many of the detailed experiments set up to discover it have turned up “much of nothing,” such as I mentioned Gizmodo in the year 2020.

“Axion – it’s always difficult to explain, but there are two reasons physicists in general are very excited about it,” Peter Graham, a theoretical physicist at Stanford University, told Gizmodo. for other reasons, but then I realized that it would actually be a naturally good candidate dark matter.”

His name for laundry detergent, axions are not described in the Standard Model of particle physics, but they do explain a frustrating problem in the field: that some of the expected properties of a neutron do not occur in nature. (Physicists, as you might expect, are big fans of Occam’s code: the idea that the simplest solution is probably the right one — there’s no need to overcomplicate things.) But in order to see if axions actually elicit this anomalous behavior in neutrons, the researchers needed to find one.


DM Pathfinder Radio, which hunts for hidden photons.
Photo: Isaac Schultz

“It’s the only really powerful way to solve this problem using the Standard Model,” said Kent Irwin, a physicist at Stanford University and SLAC. and the principal investigator for Dark Matter Radio, he told Gizmodo. “Regardless of dark matter, if the axon wasn’t there, it would cause real headaches for the Standard Model.”

The Dark Matter Radio Project attempts to discover hidden photons in a specific frequency range by systematically rotating the disk, in what amounts to a patient, exhaustive search for wavelengths Where the sound of such a particle can be made. Subsequent generations of radio would hunt for axions.

As far as subatomic particles go, some are only very small, while others are extremely tiny. Some are massive enough to detect collisions with other matter relatively easily, such as collisions that occur in particle collisions. Other particles behave so elusive that they are easy to detect as waves, due to how far they travel through space.

“[An axion] It is so light that quantum mechanics tells you that it actually has to propagate over a very large distance,” Graham said. “You can think of it more as a background wave, a background fluid that you’re kind of immersed in.”

If the dark matter is at least partial axons or hidden photons, then the matter flows through you and passes me in great numbers every second. Like neutrinos, theoretical particles are ubiquitous in ordinary matter at one time due to their abundance and practically surpassed by them due to the smallness of their interaction with them. The axial waves scatter as they are supposed to be anywhere from a few feet to football fields.

That’s why Radio Dark Matter looks for dark matter particles by looking for their background, or a specific frequency they travel on, similar to how a particular radio wave can be picked up only on the frequency it’s broadcasting. This particular radio needs to be shielded from any other type of wave, so it’s immersed in a helium dewar cooled to just above absolute zero. (A dewar is essentially a vacuum flask — in this case a vessel — to keep materials at a certain temperature, in this case to keep helium super-cold.)

The current Dark Matter Radio experience is the prototype, or Pathfinder, of larger projects down the line. It consists of a liter-sized cylinder made of superconducting niobium metal, around which a tightly coiled niobium wire. A bit like someone winding the strings of a guitar on the vertical axis of the reel instead of on its horizontal axis. This is the Pathfinder inductor. If the hidden photon resonates at the frequency that the Pathfinder is set to pass through, the change in the magnetic field will induce a voltage around the strange inductor.

A DM radio for physicists.

The rig the Pathfinder Radio DM is mounted on when submerged in helium.
Photo: Isaac Schultz

said Stephen Kuenstner, a physicist at Stanford University and a member of the DM Radio team. The hidden photons “can pass through the box and have some potential to interact with the circuit in the same way a radio wave might,” Kuestner said.

To amplify any signal the Pathfinder picks up, a hexagonal niobium plate shield encases the aforementioned components that act as a capacitor. This amplified signal is then transmitted to a quantum sensor called a SQUID (Superconducting Quantum Interferometer), a technology invented by Ford Motor Company in the 1960s. The squid lives at the bottom of the radio and measures and records any signals it picks up.

The smaller the expected mass of an axion becomes, the more elusive the particle will be, because its interactions with ordinary matter proportional to its mass. It is therefore important that the next generation of DM radio becomes more sensitive. The way to set up the experiment, “The frequency on the disk is the axon mass,” Irwin said. Appropriate! The mass of these particles does not compare to even the smallest things you might think of, like atoms or quarks. These particles will be somewhere between a trillion and a millionth of an electron volt, The electronvolt is about a billionth the mass of a proton.

The Pathfinder room is comfortable, much like a normal physics lab, but for the seemingly menacing platform that plunges Pathfinders into helium and large helium tanks attached to the wall in case of earthquakes. In 1989, Irwin was a graduate student at Stanford University and was working in the university’s basements when a 6.9-magnitude Loma Prieta earthquake shook the area, sending fire extinguishers off walls. It’s safe to say the lab doesn’t take any chances with helium (although it’s not flammable, the gas can displace oxygen, causing suffocation).

Gaseous Pathfinder helium uses and stays relatively warm 4 K (in other words, four degrees above absolute zero), but the next experiment – the 50L dark matter radio – will use liquid helium, cooled to less than one degree above absolute zero. All the better to hear dark matter using.

The DM 50L radio is in the corner of a large room in the Hansen Experimental Physics Laboratory at Stanford. The room looks a bit like the TV room at the Willy Wonka Factory; It has high ceilings, lots of obscure equipment, and a stark white color. Two 6-foot relief refrigerators on one side, adjacent to a deep cabinet, are the radios. The two machines are fed with gaseous helium held in tanks in the next room, and then cooled to liquid helium as cold as 2 K. Magnets inside the gold-plated copper and aluminum casings will turn any detected axes into radio waves for physicists to interpret.

“The particle physics community is — and that analogy is often said — just like a barge. It takes time and has a lot of momentum,” Irwin said. “So although I think there is a lot of reason to believe that radio-like dark matter signals are more attractive — the signals Pivotal – From WIMPs, there are still a lot of giant experiments out there looking for little things, which is a good thing.”

A horizontal relief refrigerator in the basement of Stanford University.

Horizontal Dilution Refrigerator, part of the DM Radio-50L Experiment.
Photo: Isaac Schultz

Other experiments include axion hunt ADMX Experience at the University of Washington divided Experience in Fermilab, and mascot Experience at MIT, and hastack Research at Yale University. DM Radio is similar to many of these, but looks for hubs in a different range. In concert, the Axion hunt group around the United States and beyond are working to limit potential audiences for the Axis.

Radio Dark Matter itself should be considered more of a family of experiments: the team is currently working with the Department of Energy on a next-generation experiment that will search for axions in a cubic meter, hence its name DM Radio-m³. In the distant future, Erwin and his team have aspirations for a project called Radio DM-GUT, which would be closer to the scale of some of the largest physics experiments on the planet.

Taken together, the experiments survey a wide area of ​​the most promising range for the axion mass. Irwin said the preferred region of the axion mass could be searched for in the next two decades using larger experiments — although the team could have simply found an axion before that time, which could end the search for the entire dark matter. With enough listening, we may have a whole new particle for textbooks. Or there may be radio silence.

More: The prime suspect of dark matter may escape from neutron stars

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