Catching Dark Matter in a Basement in Neutrino Alley

Dark Matter Sub-Atomic Particle Artist's Concept

This illustration represents a dark matter particle. Scientists at Oak Ridge National Laboratory attempted to observe these elusive particles using their neutrino detectors in Neutrino Alley.

Scientists at Oak Ridge National Laboratory attempted to observe dark matter in a brightly-lit hallway in the basement using the sensitivity of their neutrino detectors. Neutrino Alley, where the team works, is located beneath the Spallation Neutron Source, a powerful particle accelerator. Following up on years of theoretical calculation, the COHERENT team set out to observe dark matter, which is believed to make up to 85% of the mass of the Universe. The experiment allowed the team to extend the worldwide search for dark matter in a new way, and they are planning to receive a much larger and more sensitive detector to improve their chances of catching dark matter particles.

Few things carry the same aura of mystery as dark matter. The name itself radiates secrecy, suggesting something hidden in the shadows of the Universe.

A collaborative team of scientists called COHERENT, including Kate Scholberg, Arts & Sciences Distinguished Professor of Physics, Phillip Barbeau, associate professor of Physics, and postdoctoral scholar Daniel Pershey, attempted to bring dark matter out of the shadows of the Universe and into a slightly less glamorous destination: a brightly lit, narrow hallway in a basement.

Not an ordinary basement, though. Working in an area of Oak Ridge National Laboratory nicknamed Neutrino Alley, the team typically focuses on subatomic particles called neutrinos. They are produced when stars die and become supernovas, or, on a more down-to-Earth level, as a by-product of proton collisions in particle accelerators.

Perseus Cluster Dark Matter

Dark matter, the invisible stuff that makes up 85% of the Universe’s matter, isn’t just hidden away between galaxies. A team of scientists is trying to bring it out of the shadows. Credit: X-ray: NASA/CXO/Fabian et al.; Radio: Gendron-Marsolais et al.; NRAO/AUI/NSF Optical: NASA, SDSS

Not coincidentally, Neutrino Alley is located directly underneath one of the most powerful particle accelerators in the world, Oak Ridge’s Spallation Neutron Source (SNS). Neutrino Alley houses a collection of detectors specifically designed to observe neutrinos as they pass through and collide with them.

Neutrinos aren’t the only by-product of SNS’s operations, though. Dark matter (not to be confused with the movie villain favorite anti-matter) is also produced when particle accelerators crash protons together. Following up on years of theoretical calculation, the COHERENT team set out to capitalize both on SNS’s power and on the sensitivity of their neutrino detectors to observe dark matter in Neutrino Alley.

“And we didn’t see it,” says Scholberg. “Of course, if we had seen it, it would have been more exciting, but not seeing it is actually a big deal.”

She explains that the fact that dark matter wasn’t observed by their neutrino detectors allows them to greatly refine the theoretical models of what dark matter looks like.

“We know exactly how the detector would respond to dark matter if dark matter had certain characteristics, so we were looking for that specific fingerprint.”

Kate Scholberg, Grayson Rich and Philip Barbeau

Kate Scholberg, co-author Grayson Rich and Philip Barbeau. Credit: Long Li /Duke University

The fingerprint in question is the way in which the nuclei of the atoms in the neutrino detector recoil when hit by a neutrino, or in this case, by a dark matter particle.

“It’s like throwing projectiles at a bowling ball on a sheet of ice,” said Pershey. The bowling balls, in his analogy, are the atoms contained in the neutrino detector — which in this experiment was a 14.6 kg cesium iodide crystal. “You can tell a lot about the projectile and the force with which it was thrown by how much the bowling ball recoils upon contact.”

When it comes to dark matter, any information is good information. No one really knows what it is. Almost 100 years ago, physicists realized that the Universe couldn’t behave the way it did if all it contained was the stuff we can see.

“We’re floating in a sea of dark matter,” said Jason Newby, group leader for neutrino research at Oak Ridge National Lab and a co-author of the study. The consensus among physicists is that dark matter makes up to 85% of the mass of the Universe. It must be subject to gravity to explain the Universe’s behavior, but it doesn’t interact with any sort of light or electromagnetic wave, appearing dark.

Jason Newby and Yuri Efremenko Hold Photosensor

Jason Newby and co-author Yuri Efremenko hold the remarkably small 14.6 kg cesium iodide neutrino detector used to search for dark matter at Neutrino Alley. Credit: Genevieve Martin/Oak Ridge National Laboratory, U.S. Dept. of Energy

“We learned about it by looking at big galaxies rotating around each other, seeing that they rotate way faster than they ought to, implying that they have more mass than they appear to have,” said Pershey. “So we know that there’s extra stuff out there, we just need to learn where to look for it.”

“Even though we’re in the realm of mostly no results,” said Newby, “it’s really important that everywhere you can look, you look, and then you can rule out a whole number of possibilities and focus on a new area with strategy rather than just using a ‘spaghetti on the wall’ approach.”

Daniel Pershey

Daniel Pershey. Credit: Duke University

“We’re extending our reach for what models for dark matter can exist, and that’s very powerful,” said Scholberg.

She points out that the achievement doesn’t stop there: the experiment also allowed the team to extend the worldwide search for dark matter in a new way.

“The typical detection technology is to go underground, build a very sensitive detector, and wait for these dark matter particles to just pass through,” said Pershey.

The problem? Dark matter particles may be traveling quite leisurely through the air. If they also happen to be very light, they may not reach the detector with enough energy to create a detectable fingerprint.

The COHERENT team experimental setup addresses this issue.

“When you go to an accelerator, you produce those particles at significantly higher energies,” said Pershey. “And that gives them a lot more oomph to knock into nuclei and make the dark matter signal appear.”

So, what now? It’s not quite back to the drawing board. Neutrino Alley is currently preparing to receive a much larger and more sensitive detector, which, combined with COHERENT’s refined search parameters, will greatly improve the chances of catching one of these devilish particles.

“We’re at the doorstep of where the dark matter should be,” said Pershey.

Reference: “First Probe of Sub-GeV Dark Matter Beyond the Cosmological Expectation with the COHERENT CsI Detector at the SNS” by D. Akimov et al., 3 February 2023, Physical Review Letters.
DOI: 10.1103/PhysRevLett.130.051803

9 Comments on "Catching Dark Matter in a Basement in Neutrino Alley"

  1. Perhaps DARK MATTER (what’s in a name?) has no physical presence in this Universe. It would be like looking for a needle in a haystack, when one doesn’t know what a needle is, much less a haystack… or the old Buddhist/Matrix conundrum: There is no spoon… I mean… One wears a coat to stay warm not to consider the “weave”. The 1950s colloquial expression “Threads” notwithstanding. Dark Matter (Gor!) perhaps, IS NOT-Matter or energy, but “merely” a “frame” of reference within which the fabric of the Visible Universe is defined.
    One would necessarily have to abandon the notion of a Finite Universe for a self-contained “ISM”, which does not conform to “one’s” Science let alone one’s expectations.
    In conclusion, a Suggestion: For the burning pain in your Heart over the Nature of “things”, take the RED Pill. The BLUE Pill is a tonic dose of Nexium.

  2. Get into Cern, dark matter there, spin in small amounts, create warp drive. Get out of this planet…

  3. Howard Jeffrey Bender, Ph.D. | April 1, 2023 at 6:51 am | Reply

    Another possibility, from a view of String Theory, is that Dark Matter appears to us as an effect of string/anti-string annihilations. As you may know, quantum mechanics requires that strings must be formed as pairs in the quantum foam – a string and an anti-string – that immediately annihilate each other. Quantum mechanics also requires both the string and anti-string to be surrounded by “jitters” that reduce their monstrous vibrating energies. What if this jitter remains for a fraction of an instant after their string/anti-string annihilations? This temporary jitter would be seen by us as matter, via E=mc2, for that instant before it too returns to the foam. That’s why we never see it – the “mass” lasts only for that instant but is repeated over and over and over, all over. Specifics on this can be found by searching YouTube for “Dark Matter – A String Theory Way”

  4. Fixed gravity for you. | April 1, 2023 at 12:29 pm | Reply

    “Dark matter” seems capable of forming concentric evenly-spaced halo effects with progressively-fading cyclic density variations. “Malin 1” shows four or five such cycles in its sharpest imaged version, trapping matter into concentric zones, as I see it, it’s supposedly the largest organized spiral galaxy, coming in at around half a million light years across. Dark matter proponents seem to want to ignore it for the greater good of curved space gravity, but it’s impossible to say, really. All a part of the lure of oversized invisible stuff, I suppose.

  5. Roger Haselhorst | April 1, 2023 at 1:35 pm | Reply

    Interested non-academic observer;
    The Standard Model, particle physics, (Higgs,quantum,magnetic)fields etc.,zero point(energy)non-empty space(quasi particles). Einstein tells us electromagnetism and matter are interchangeable (simplified) within the framework of spacetime and gravity. If quasiparticles and zero point energy(clue?) permeating space were mere potential until matter encountered, then could it at galactic scales, as the god field gives mass to Higgs Boson, explain galactic rotation without need to conjure the majority of the universe from nothing? Maybe not,but it seems that a better understanding of something we think we know is a much more elegant solution than something from nothing.

  6. Charles G. Shaver | April 1, 2023 at 2:10 pm | Reply

    Since 2009, in my model of the universe gravity is simply pulsing coherent curling, coiling and spiraling lines of universally attractive force perpendicular to their lengths radiating across the universe from all disparate objects with their respective fields of gravity, in accordance with the inverse-square law of attraction. As “gravity lensing” demonstrates, even photons in transit have sufficient mass to be affected by fields of gravity as they pass massive objects enroute to the earth.

    The problem with the standard model is long ago with classic double-slit experiments it was assumed that the scattering of impacts on the target was due to a dual nature of small particles to be both particles and waves; not. Pulsing lines of gravity force are what direct the particles to one slit or the other. My low budget lay at-home experiments with rotating wheels since 2012 have informed me that rotation of an object can affect the density/strength of that object’s field of gravity. And, with most (if not all) objects in space rotating at one rate or another, what is thought to be dark matter is rotationally intensified gravity, and dark energy is non-existent.

    Photons accelerate leaving a source in an expanding field of gravity (blue shift) and decelerate when entering our contracting field of gravity (red shift); the age and size of the universe still need to be determined, it may be collapsing, static or expanding, as I see the possibilities. My question is: what is it that’s inducing those lines of gravity force to radiate from all of those cosmic objects?

  7. Fixed gravity for you. | April 3, 2023 at 6:14 am | Reply

    Frequency of light particle occurrence has nothing to do with the frequency of light waves, one reason why it’s tricky but not wise to suppose gravitational redshift is evidence of two different rates of time. Another reason would be that it’s not good to suggest imaginary violations in energy conservation are real when around religious cranks.

    Another problem with the religion of relativity is it encourages religious cranks by offering no satisfactory explanation for those strange eye-shaped galaxies except to invent more invisible refuse to go along with their bent nothing issues. So, you’ll never hear about conservation of anything physical, let alone pitch momentum, in radiated gravity information carriers.

    Another problem with the religion of relativity is it implies space is full of large invisible things when in all likelihood all the invisible things in the universe are invisible because they’re too small to see.

    Another problem with the religion of relativity is that Maxwell gets the blame for making Einstein think the speed of light should be constant in variable gravity. It also supposes the universe cares about keeping the speed of light constant, especially as it shortens the lengths of equations.

    The religion of relativity preserves an opportunistic “what you saw is what you got” ethic, while focusing on youth and pretending it’s problems are useful for GPS calibrations and that wormholes will some day explain entanglements.

    Another problem with the religion of relativity is it motivates religious and non-religious cranks to conceal the authoritarian lack of logic it carries as it has historically perversely associated unbent space with inhuman behavior. Fascists like it, however, so there is that.

  8. What if our assumption that gravity is what is holding galaxies and solar system together is wrong? What if our understanding of gravity is so flawed that we think 85% of the mass of the universe is some esoteric matter we can’t detect? Just look at the Earth and the Sun. If the sun was the size of a basketball, the Earth would be the size of the tip of a ball point pen over 1000 linear feet away! How much gravitational interaction would there be between even a solid lead basketball and the tip of a pen two blocks away? Zero to quite a few decimal places. Something else is holding galaxies and our solar system together or our theories of gravity are way off.

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