On Sept. 1, scientists searching for evidence of dark matter unveiled their analysis of an unusual event recorded in 2024. Their findings, though not yet proven, could be a significant clue to the presence of the unseen stuff that is theorized to make up a quarter of the mass of the universe.
A team of researchers around the world probed the anomaly detected at the LUX-ZEPLIN experiment, which is located deep underground in South Dakota.
Two University at Albany physicists involved in the study, Matthew Szydagis and Cecilia Levy spoke with WAMC’s Lucas Willard.
INTERVIEW TRANSCRIPT
Editor's note: this conversation has been lightly edited for clarity.
Levy: I always say this. It's a great analogy. It's like the wind. How do you know the wind is there? You see the leaves move in the tree, but you can't actually see the wind. So, same thing with dark matter. that's how we know it's there because we see its effects on stars and galaxies and in astronomy in space, right? But we haven't actually detected the particles that it's made of.
Willard: So, there's been a search for dark matter, and we're going to be talking about this big underground facility in South Dakota, which has a lot of scientific equipment that I have no idea how it works. But this, it's a mile underground, and it's a really big technical marvel. But maybe Matthew, can you tell me a little bit about the LZ over in South Dakota?
Szydagis: Cecilia and I work on the LZ experiment, which is a large vat of liquid xenon.
'Why liquid xenon?' You might ask.
It's a general good detector of particles, so it can detect regular types of particles we already know and love — alphas, betas, gamma rays-and so it's a general particle detector.
Why we think it could also detect dark matter, is, because we are shielding it against all those well-known particles we already know about by deploying it deep underground, nearly a mile underground in South Dakota, and so that's going to help with prevention of cosmic rays of naturally occurring cosmic radiation, and it's also even that's not good enough because rocks the cavern walls are just naturally radioactive to a very, very, small amount, just like the human body, and so, in addition to being underground, we also shield the LZ experiment with many additional layers.
We've got a water tank that the liquid xenon sits at the center of, and between the xenon and the water tank, there's also what's called the outer detector that's made up of different components to tag neutrons, gammas, those other particles that we already know about, in order to reduce the probability of a false positive.
Willard: So what happens when a particle that may signify dark matter actually interacts, travels through space, through the mile of Earth, into this big vat of xenon deep underground in this former gold mine. What actually happens? What is the equipment actually looking for?
Levy: Super simple. Light. We're looking at two signals of light, two flashes.
Willard: So, something actually glows in the tank?
Levy: Sure. You can say this. Yes. So, we have we have light sensors in the on the detector at the bottom and at the top we have a lot of light sensors, and so what happens is that you get a first light signal and then after that you also get charge, and so we apply an electric field because electric fields actually move charge charges, and so the charges drift up, and then they hit some more xenon, and then they create a second flash of light.
Willard: So on Sept. 1, there was this release of findings of an analysis from an anomaly that happened a couple of years ago.
So, obviously, it takes a lot of time to to look at all this stuff. I imagine it's a little bit more than looking for a needle in a haystack. But what was this anomaly that was actually recorded, and what went into this analysis that clues us into, 'hey, this is pretty significant in the search for dark matter.'
Szydagis: Well, we have an event that is in a region of parameter space in the in the results where we don't expect to see anything from known sources of background noise.
Those well known particles I was talking about earlier, but we had been sitting on this event for about a couple years, because before publishing something that could be potentially interpreted as a dark matter signal, we wanted to be absolutely sure there wasn't some source of background that we had not considered - we had forgotten. It's also important to keep in mind, we are only talking about one event, so it is extremely far from being conclusive.
The reason why there is still reason for excitement and why there's been excitement is because it's in a region where we don't expect any background noise from known types of particles.
Willard: Is this the first time from this event a couple of years ago that the detector, this big vat of xenon, actually recorded this flash of light that was sort of an anomaly that could point to evidence of dark matter?
Levy: So, we see all the time a whole bunch of light, right? So there's there's always reaction. Tons of things, right? But yes, this is the first time that we see something that we legitimately cannot explain, and so that does not mean it is dark matter. I really want to be very clear about this. We don't know where scientists were being very cautious, but I can tell you, for two years we've been looking and looking and trying to like think about backgrounds and explain it, etc. and we haven't been able to.
Willard: I think it's fascinating, just zooming out for a second, that we have this research right now. Well, this facility is far away in South Dakota, but this is news that went around the world, and now, I'm talking to two UAlbany physicists that happen to have some handle in the analysis of this data. It's pretty interesting, and just an illustration of how science is really local here about something that seems so abstract.
Szydagis: I think it's up to nearly 40 institutions now worldwide. So, the LZ experiment has, even though the physical experiment is deployed deep underground South Dakota, it is not just an American experiment. There are tons of U.S. institutions and labs, but we also have members from the U.K. Australia, Portugal, South Korea. I might be forgetting a country or or continent even, so it's really a multinational effort, and Cecilia and I have been part of this for for many years now, and throughout our careers we've been on similar or different experiments because there are so many different experiments looking for dark matter, and right now I think we're honored to be to have been for many years now, a part of really the the number one world leading experiment for a particular type of dark matter because we don't know exactly what dark matter is, what its mass is.
So, there are different types of experiment, but for the types of heavy dark matter particle that LZ is geared for, it's really the best experiment in the world right now.
Levy: So, yes, this experiment is very much multinational, but it is vastly funded by the Department of Energy, so this is who gives us our funding. So, this is the federal government, and to answer also, maybe a little bit more directly your question, I think that what's fascinating with science, is at the end, science is the great unifier, and so I think that this is really for me. I really enjoy just even being able to just talk to people and it doesn't matter who — I will talk to anybody about it because I think that that is part of being what a scientist is — you have to be an educator at heart, and you want to be able to share your knowledge. You also have to be very careful, right? Like again, we hold ourselves at the highest of the highest standards of integrity, but sharing it, I think, is really part of the thrill.
