Did We Detect Dark Matter… or Fool Ourselves?

Please join my mailing list here 👉 https://briankeating.com/yt to win a meteorite 💥 What if 85% of the universe is invisible—and the one experiment claiming to have found it is wrong? For nearly three decades, Italian physicists have claimed their DAMA/LIBRA experiment detected the elusive particles that make up dark matter—the mysterious substance holding galaxies together. Yet no one else has ever confirmed it. Join Brian Keating, UCSD cosmologist and host of The INTO THE IMPOSSIBLE Podcast, as he visits Kaixuan Ni and his team—scientists building the world’s most sensitive detectors deep underground—to uncover: • ⚛️ How detectors using liquid xenon can “fingerprint” single atomic collisions. • 💡 Why dark matter’s “heartbeat” signal divided physicists for 30 years. • ☢️ How dark-matter detectors are now being repurposed to detect nuclear weapons and monitor reactors remotely. • 🌞 The shocking discovery of solar neutrinos and ultra-rare nuclear decays—phenomena rarer than the age of the universe itself. This is the invisible architecture of reality—where cosmology meets particle physics, and theory meets obsession. 📍 Filmed at UC San Diego’s Mayer Hall and Harold Urey Hall — home to experiments that may finally prove what 85% of the cosmos is made of. 👇 Watch till the end to see how a failed dark-matter search could save the world from nuclear war. Key Takeaways: 00:00 "Dark Matter Detection Debate" 04:51 "Physics, Peace, and Deuterium" 08:20 "Annual Modulation from Dark Matter" 10:05 Particle Physics' Atomic Fingerprinting Revolution 16:03 "Data Processing for Dark Matter" 18:56 "Boron-8 Neutrinos Observed" 22:43 "Exploring Electron Recall Signal Excess" 24:22 "Xenon Experiment Resolves Signal Mystery" 30:11 S1, S2 Signal Discrimination 33:11 "Radon Control for Clean Detection" 34:26 "From Cosmic Mysteries to Peace" 38:10 Dark Matter: Undetected Mystery 🎥 Directed & Narrated by: Brian Keating 🔬 Featuring: Prof. Kaixuan Ni, Prof. Liang Yang, Zihao Shi (Columbia) 📍 Location: UC San Diego 🎙️ From The Professor Keating Experiments series Join this channel to get access to perks like monthly Office Hours: https://www.youtube.com/channel/UCmXH_moPhfkqCk6S3b9RWuw/join My tell-all cosmic memoir Losing the Nobel Prize: http://amzn.to/2sa5UpA Follow me to ask questions of my guests: 🏄‍♂️ Twitter: https://twitter.com/DrBrianKeating 🔔 Subscribe https://www.youtube.com/DrBrianKeating?sub_confirmation=1 📝 Join my mailing list; just click here http://briankeating.com/list ✍️ Detailed Blog posts here: https://briankeating.com/blog 🎙️ Listen on audio-only platforms: https://briankeating.com/podcas Learn more about your ad choices. Visit megaphone.fm/adchoices

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Speaker 00

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• 0:56Speaker 02

  For a hundred years, we've sensed the presence of an invisible force: dark matter. First proposed by Fritz Zwicky in the 1930s, and later confirmed, beyond a reasonable doubt, by Vera Rubin herself. What would the universe look like without dark matter? Galaxies would still form, but they'd fly apart. Their outer stars would spin off like sparks from a pinwheel. In 1933, Fritz Zwicky noticed this problem in galaxies within the Coma Cluster. The visible matter couldn't account for the galaxy speeds he observed. He called it dunkelnaturi, dark matter. Decades later, Vera Rubin found the same mystery in spiral galaxies.

• 1:41Speaker 02

  Stars far from the center weren't slowing down. Rotation curves were flat. Speeding up, an astronomical anomaly begging for an invisible explanation. Imagine two galaxies, one governed by Newton's laws alone, and one with an unseen halo of dark matter. In the dark matter-rich galaxy, stars at the outer edges orbit almost as swiftly as those near the center. This observation is a cornerstone of the dark matter hypothesis. It suggests not only that there's an unseen mass enveloping the galaxy, but that the dark matter would produce a telltale heartbeat revealing its presence. This iron ball is heating to 3,000 degrees.

• 2:22Speaker 02

  As it glows, it's radiating light across the electromagnetic spectrum. We can see it, we can measure it, we can interact with it. This is normal matter, behaving exactly as we expect. It's dark and it's matter, but it's not dark matter. In most of the universe, it's nothing like this ball. Picture this: you're hunting for something that makes up 85% of the universe, but you've never seen it, can't touch it, and you aren't even sure you can prove that it exists. Your detector sits a mile underground, colder than Antarctica, waiting for a collision that might happen once in a decade. And when it finally does, you're not even sure it's real. That's exactly what happened to my guest today. And what he discovered next will completely change how you think

• 3:07Speaker 02

  about the invisible universe around us.

• 3:10Speaker 03

  I knew this DAMA result since I was a undergrad student in 1995. From experimental point of view, other experiments, almost all of these experiments that are more sensitive than DAMA have already exude that particular signal.

• 3:26Speaker 02

  Imagine Earth plowing through a cosmic headwind of invisible particles, dark matter particles. As our planet circles the Sun, we glide on a helix, riding through that dark matter wind. Sometimes we push against it, sometimes it blows with us. In March, the Earth trails behind the Sun. By June, it charges straight into the stream. The signal peaks. Six months later, the Earth swings around, moves away, and the wind slackens. It's then when the signal dips. And then the pattern repeats orbit after orbit, year after year. This annual rise and fall is the telltale heartbeat scientists have been searching for, the faint whisper of dark matter.

• 4:08Speaker 02

  And this signal is what the Dama-Libra experiment claims to have seen, not just for one or two years, but for nearly the past 30 years. The signal that piqued Caishuan's interest 30 years ago was produced by the Dama-Libra experiment. It shows the telltale pulse of our cosmic dance around the sun as the sun itself moves around our galaxy. The predictions of the dark matter model match exactly on what Dama-Libra has observed. So why don't all of Caishuan's colleagues agree that Dama has made the definitive detection? Right here, on the campus of UC San Diego, scientists are working to see the invisibility,

• 4:51Speaker 02

  the missing matter that makes up most of the matter in the universe. What they do is very complementary to what scientists using cosmic microwave background do. We're all in the same team, although it's claimed that scientists, competitors, have seen a dark matter signal for over 30 years. This signal remains controversial. We'll explore the nature of that signal, how it was made, how it was first detected, and why colleagues are very skeptical about it. We'll interview the primary players in the new generation of searches using liquid noble gases like xenoc,

• 5:32Speaker 02

  fighting against backgrounds, man-made, natural, and cosmic in nature. We'll reveal the techniques and technologies that spin off from this research in a fascinating way that this research into cosmology and particle physics may pay dividends in helping maintain peace, detect rogue nuclear weapons, and even prevent a nuclear war.

• 6:01Speaker 02

  All this happens not far from UCSD's famous Yuri Holm, named after Harold Yuri. He's famous for many things. He was the first person to detect and measure the properties of deuterium, which plays an enormous role, not only in particle physics, but in cosmology as well. The abundance of deuterium is one of the best pieces of evidence that we have that the Big Bang occurred. Its abundance ratio matches almost perfectly the expectations that one would get from an early universe which is extremely hot, extremely dense, a fiery furnace, fusing

• 6:46Speaker 02

  proton to neutron. And that may seem implausible. How can a neutron, which is neutral, bind to a proton, which is positive? Well, that's what Harold Yuri figured out, measuring heavy hydrogen, paving the way for the measurement of tritium, which is radioactively unstable. We've named our building, the chemistry department, is named after him, won the Nobel Prize for his discovery. Before we dive into the controversy that's been tearing the physics community apart for 30 years, you need to understand what's at stake here. If the Italian experiment we're about to discuss is right, Dama Libra, it's the discovery of the century. If they're wrong, it's the most persistent false signal in human history.

• 7:31Speaker 02

  And what makes this extraordinary? My friend, Professor Taishan Ni at UC San Diego, is about to tell us why he spent his entire career trying either to confirm or debunk a claim that inspired him as a 20-year-old kid back in 1995. That was 30 years ago, three decades, his whole life's obsession. And the signal, well, it's still dividing scientists to this very day. The universe would look very different without dark matter. Galaxies would spin much slower than they're observed to spin. The Earth following the Sun trails at a much faster rate than would be expected if there was no dark matter in our galaxy. Can you explain what the current thinking is of this experimental result?

• 8:16Speaker 02

  They claim 20 sigma detection. They've measured it since 30 years now, and yet they're the only ones that believe it. So what is the state of perception of this result within your field? Is it a detection? Is it definitely not a detection or somewhere between?

• 8:33Speaker 03

  Yeah, I knew this DAMA result since I was a undergrad student, right? 1995. And that probably triggered me to come to US to study dark matter. But still exists now that the conflict without experiments. And so from experimental point of view, almost all of these experiments that are more sensitive than DAMA have already explored that particular signal. So they detect something, but something might not be dark matter. Might be some background that remain in their detector.

• 9:11Speaker 02

  Can you explain the principle behind the annual modulation technique?

• 9:16Speaker 03

  So annual modulation is really coming from like dark matter. And the dark matter is in our galaxy, right? Or so on the Earth. And the Sun is moving around the galaxy. So it has a speed. So basically, the Sun has a relative motion with the dark matter halo we call it. And the Earth is rotating around the Sun, right? So in June, when the Earth is rotating in the same direction as Sun, the speed relative to the dark matter halo is larger than in December, when the Earth is rotating in the opposite direction with Sun. So that different speed making the event rate different in the detector.

• 9:59Speaker 03

  In June and December, there could be a 5%, 10% of variations as we call annual modulation. So if we detect such an annual modulation with a lot of variance, that could be a confirmation of, you know, dark matter signal. As it could be.

• 10:16Speaker 04

  Because there are other background, but also marginally at the same phase, such as cosmic ray neons interacting. And I'll go detect.

• 10:26Brian Keating?

  But those three experiments are all in the northern hemisphere. Is there a plan to build an identical copy of DAMA or something cosine based in the southern hemisphere? With that annual modulation.

• 10:37Speaker 04

  Poses trying to build a, for example, I believe the SAB experiment in the southern in Australia. Boom, has southern hemisphere. Could make, you know, the modulation, maybe the the phase different compared to the other hemisphere. Um, but that experiment is you, um, you know, kind of that's beauty.

• 11:00Speaker 02

  Yeah. Hold on to what you've just heard about seasonal modulation, because in a minute, Professor Ni is going to reveal the technology that makes his detectors fundamentally different from the controversial Italian experiment called DAMA Libra. What he's about to describe sounds like science fiction. A chamber that can fingerprint individual particle collisions at the atomic level? It's like CSI particle physics. And that fingerprinting capability, that's exactly why the physics community is so divided about the 30 year old claim of success by the DAMA Libra experiment. No other event in scientific history has lasted so long without confirmation and yet been accepted by so many as being truth.

• 11:42Brian Keating?

  Can you explain the way that xenon detector system, your experiment works? What is a dual phase time projection chamber, TPC?

• 11:50Speaker 03

  So we use a dual phase. We call dual phase time projection chamber is mainly a liquid phase. This is the main target for interacting with the dark matter. And above that is a gas phase. And we need a gas phase because we want to amplify the signals. The dark matter detect very low end a signal in the liquid zena and then produce ionization. And this ionization had to be drifted into the gas phase. So any tiny sub KV bands can be amplified. One electron can be amplified by a hundred times, a thousand times. Turn into light and then we can detect these tiny energies. That's the main, you know, advantage of dofit.

• 12:35Speaker 02

  Yeah, time projection sounds very futuristic. What does it actually mean? Time projection in a chamber, TPC.

• 12:42Speaker 03

  So it's first, you know, we have one interaction and then ionization start to drift, right? So there's a time. So we will know the time and this time tells you the event position in this direction. So that's where the time comes. And projection, sometime you can also think of as, you know, in our case, this event will eventually will be ionization charge will be drift on the top and it will give you localize the signal. And this local and give you the kind of a position in this direction, X, Y direction. So that give you kind of projection.

• 13:24Speaker 02

  Okay. And so it's very different than the than the DAMA experiment. DAMA is scintillation, dark matter, if it exists, comes in and there's a reaction that causes a pulse of light effectively, correct?

• 13:38Speaker 03

  That's right, DAMA use the scintillation. We also use scintillation, you know, before the ionization charge drift, we also have a direct scintillation, but we have two signals. So these two signals will tell you actually the difference between many background from the actual signal. DAMA, I believe, is just using the scintillation, the crystal is actually scintillation crystal. Their scintillation crystal is also very pure, you know, very clean. And they detect these scintillation pulses and trying to look for them into whether or they cannot tell the difference between a nuclear recoil or electron recoils or backgrounds,

• 14:19Speaker 03

  but they can just count how many events to the lowest energy possible and then use a modulation as information.

• 14:27Speaker 02

  Ah, so it has less.

• 14:30Speaker 03

  Diffusion. Yes. Yeah.

• 14:32Speaker 02

  I want to pause here and give you some perspective on what we're talking about. The interaction Professor Nee just described, a dark matter particle hitting a xenon atom, would be like a mosquito flying into a freight train and somehow leaving a trace in the freight train's trajectory that we could still measure. The precision required is almost supernatural. And yet, he and his colleagues, team and friend, including past guest Elena April, have built machines that can do exactly that. So if they're so good, if they're so sensitive, why can't they confirm a signal that's been reported since Bill Clinton was president? So we mentioned the, some of the concerns about the DAMA results or reproducibility and confirmation.

• 15:14Speaker 02

  Why has it been so hard for other researchers to confirm or refute the DAMA Libra results?

• 15:21Speaker 03

  I, I think one thing, the mental point is you need to get very clean crystals, very pure crystals. If your crystal is, has in some radioactive contaminants that continues emitting background, then basically you cannot see as clean as DAMA can see.

• 15:41Speaker 03

  The technology actually accompanying maybe is not, you know, open to the public. So other people who want to use this, the same type of crystals. For example, I believe Princeton University actually grow their own crystals for the SABR experiment.

• 16:01Speaker 02

  So if you were to meet a hypothetical student who is interested in working on DAMA for their PhD, how would you advise them? What would you say to them?

• 16:10Speaker 03

  Oh. Working on DAMA or working on SABR, for example, confirmation.

• 16:16Speaker 02

  First DAMA, yeah.

• 16:18Speaker 03

  So I would advise student to say, look into the data. Really understand the background at the lowest energy possible.

• 16:28Speaker 03

  And see if there's any systematic or other background that we haven't found or the collaboration hasn't found to see that can also produce a modulation signal. That could be, you know, a very large contribution to the community. If you, you know, still want to work on the Tomax pair.

• 16:49Speaker 02

  How does Zenon's, your project, how does it handle sharing data, making data public or accessible to the community? Does it or does it keep it proprietary?

• 16:59Speaker 03

  So, you know, the data we take, you know, that he mentioned as petabytes of data is the initial is very, you know, not noisy and full of, you know, contamination. You have to understand or are detecting in order to use that data. So even if it's to a public, it's difficult to use. But we do all kinds of data selection, cuts, and eventually produce, you know, these selected events. And that we use them to produce so-called limits. We don't find dark matter. And, and these data, once we publish our paper, we describe all the methods. And these data are also attached to these papers, making them public.

• 17:42Speaker 03

  So people, for example, want to check our signal, check our signal detecting efficiency. You can look at these data. If they want to use them to constrain other type of dark matter models, they can also use this data. And if people are interested in, you know, more experimental part of our background, then I would, you know, welcome to join our collaboration. Yeah.

• 18:07Speaker 02

  Here's where the story takes an unexpected turn that, quite frankly, keeps physicists up at night. While hunting for dark matter, Professor Ni's team stumbled upon something they never intended to find. Particles streaming from the core of our sun, passing through your body right now, completely undetected. They filtered petabytes of data. They used machine learning and AI to identify patterns and found exactly 11 events out of millions of possibilities. The amount of haystack that needs to be thrown out to find that one needle is truly extraordinary. This is detective work at the level of individual atoms. And what they've discovered makes finding dark matter, unfortunately.

• 18:50Speaker 02

  Even harder. What is the most significant source of contamination or systematic effects both in the laboratory and in the cosmos, astrophysical systematics and terrestrial systematics?

• 19:05Speaker 03

  I think mostly background, right? I mentioned, you know, the backgrounds coming from all kinds of sources, from detected material and from astrophysical source like neutrinos. So in our current generation experiment, the most background is coming from detected material, say radon in the xenon. And it depends on what type of a signal you're looking for.

• 19:33Speaker 03

  And but for our next generation experiment, solar neutrino will become another dominant background.

• 19:42Speaker 02

  You mentioned there was a recent detection and publication, in fact, I think about the solar neutrino detector properties of xenon. Can you explain that result?

• 19:52Speaker 03

  So. So the sun produced abundant neutrinos, right? And from the PP fusion and there's a reaction chains. So they are producing different kind of neutrinos. We call them PP neutrino, we call boron eight neutrinos and different energy, different spectrums. And last year, the paper we actually released is about observing about 12, 11 neutrino from so-called PP, boron eight neutrinos. And these neutrinos produce a nuclear recoil in our detector, very low energy nuclear, like about KEV, and very difficult to detect.

• 20:33Speaker 03

  And and we managed to do all kind of analysis technique, including machine learning, you know, trying to filter out all the noises. And eventually found 11 these kind of events out of a total 37 events we detected, another 26 are backgrounds. And these are the result we call a first detection of solar neutrinos in the liquid xenon detector. And that makes our experiment in the future will be more difficult to observe dark matter around six GeV, which produce the same type of spectrum as the BORON 8 solar

• 21:17Speaker 03

  detection in our detector.

• 21:19Speaker 02

  Okay. Speaking of precision, Professor Ni is about to tell us about witnessing something that happens so rarely, it makes winning every single lottery on earth look like the odds of Manny Machado hitting a home run. We're talking about nuclear decay, nuclear decay with a half-life probability of reduction by half, longer than the age of the universe. And Professor Ni and his team, well, they caught that happening multiple times. So if they can detect something with this impossible rarity, why does dark matter mystery elude them?

• 21:57Speaker 02

  About three years ago, when you were first on my podcast during COVID, four years ago, maybe, I'm not sure.

• 22:03Speaker 03

  Oh, yeah, I remember that.

• 22:04Speaker 02

  It was a detection of a very rare decay or some very rare nuclear process. Can you explain that and what the latest findings are from your research on that? Strontium?

• 22:16Speaker 03

  Yeah, I remember. So there was several observations in the past five, six years. One is so-called double electron capture of a xenon 124 element in our detector. And that's a very rare decay, you know? Electron capture is very often, but double electron capture, having two electron capture at the same time, it's very rare. The half-life of that process is 10 to the 22 years. It's very long. That's probably the longest half-life direct decay that we detect directly in a detector.

• 22:53Speaker 03

  And at that time, I think we observe about three, four sigma. And then later, you know, we could have more data and it's five, six, even more than that. Other experiment like Pana X and I believe A O Z also see these signals later. And this is just standard model process, just very difficult to detect. That's the double electron pepper we observe. But I think one thing that we actually talked about is some excess signal coming from our very low energy electron recall from a Zeno one ton experiment. Yeah. So at the time, you know, actually a grad student from UCST, Jin Changyi, you know, he's a professor.

• 23:35Speaker 03

  He and another student from Chicago, they found some excess signals in our electron recall, not nuclear recall, electron recall background. And trying to expand with all kind of background we know, and there's still the excess, you know. And eventually we think maybe these could be some background we don't know. We didn't count into, for example, tritium. That's weak. But you know, that that tritium must be very low. We couldn't detect them. So that's one possibility. But there could be also more exotic explanation.

• 24:18Speaker 03

  Say the neutrinos may have a magnetic moment, a solar neutrino may have a magnetic moment that can produce a higher rate than we expected, or maybe solar axion. So that's the paper we wrote and trying to explain excess. We don't have, we didn't have any conclusion, but that's some possibility for the excess.

• 24:37Speaker 02

  What you're about to hear is why I love experimental physics. Professor Ni's team thought they may have detected something exotic, possibly solar axions or neutrinos with magnetic moments, the kind of discovery that would rewrite textbooks. But then, then they had to build a cleaner detector. And unfortunately for them, their signal, their possible Nobel Prize, well, it disappeared, perhaps for the time being only. But honestly, this is how good science works. It's exactly the kind of story that I love to tell. And that makes the 30 year Dhamma Libra controversy so frustrating, but also so energizing.

• 25:18Speaker 03

  So later, you know, after during a COVID P P, we assembled a xenon and ton experiment. It was larger, cleaner. We made a lot of effort trying to remove for, you know, to heat a detector before we actually feel xenon trying to remove this kind of tritium if there is anything exists, right? And when we start take a data in much lower background, we didn't, the excess is gone, right? We didn't find any excess. So that means, you know, the explanation of tritium could be the right explanation, not solar axion or solar magnetic neutrino magnet moment. So that's like a kind of a, I think, you know,

• 26:03Speaker 03

  for example, we mentioned about DAMA, right? If there's excess, you could explain with dark matter, but there could also be background. And then try and do more experiment, trying to prove or, you know, refute such hypothesis. And that's what we did from zero one ton to zero N ton. We claim a signal and now we are looking, for example, when we detect, collect more data, continue to looking for, for solar neutrinos.

• 26:36Speaker 02

  I can neutrino, which is neutral, have a magnetic moment?

• 26:39Speaker 03

  Um, well, in, in the standard model, a neutrino may not have a magnetic moment, a very low, tiny that we would never see. But there are some exotic theories beyond the standard model that has a larger magnetic moment. That's physicists trying to see, you know, if we see such kind of a large magnetic moment, that could be something new.

• 27:01Speaker 02

  And how, how does it compare to like Zeppelin and Lux and the other, you know, double beta decay, neutrino less double beta decay, which look for the electron spectrum.

• 27:11Speaker 03

  Right, there are different isotopes and for. For people using liquid xenon, that's a xenon one thirty six. Like Nexo collaboration, LZ collaboration, they all have this xenon one thirty six elements. And even dedicated, for example, Canland Zen. And but you know, for LZ and xenon Anton, the element xenon one thirty six, it now detects not enough to to get the same sensitivity as the dedicated each and another double beta experiment. So but in the future, xenon and LZ, and also the Darwin collaboration in Europe, we join together to build a so-called next generation XLZD experiment.

• 27:56Speaker 03

  That eventually contains sixty to eighty ton of liquid xenon, natural liquid xenon. And that will contain about six to eight ton of xenon one thirty six element. That will push the neutrinos with double beta, they have five xenon to have to limit about ten, ten to the twenty seven, ten to the twenty eight years. Wow. And that will be a very sensitive experiment in that process as well. So Dr. Brian Kitting. Hello. These are the students, Ba, Xin Yang and Da Chen, they are three from Columbia University. Okay, well. Yeah, they are senior graduate students working on the xenon. Yeah, and yours is my student. Oh, really? Yeah.

• 28:40Speaker 03

  We're um, we're future detectors. And you know, in the, our dark matter search experiment, xenon is locating in, in the underground lab in Italy, Gran Sasso Underground in Italy. And it's a huge tank full of liquid xenon, um, total about six ton of liquid xenon in the target waiting for dark matter interactions. But here you see it's very tiny detector, right? So, um, but very similar, you know, we have a cryogenic system, we have purification system, uh, we have data acquisition system.

• 29:18Speaker 03

  And here is a little detector we're trying to build for, you know, for different applications.

• 29:23Speaker 02

  Is that like a prototype or is that hype?

• 29:25Speaker 03

  Okay.

• 29:25Speaker 02

  It's also for dark matter, for neutrinos or some other?

• 29:28Speaker 03

  Um, they wanna use it for detecting reacting neutrinos. Uh, you know, the neutrino can also interact with the, with the detector producing a signal very similar to dark matter would produce. So um, you're trying to use the same principle of detector, but reacting use a very low energy and produce nuclear very low energy nuclear very difficult to detect. Yeah, so um, I have another setup downstairs and a high bay, which is slightly bigger than this. Um, that we eventually be built uh as a reactive neutrino detector. So you could find our xenon, the xenon is contained in these uh high pressure bottles.

• 30:07Speaker 03

  And because they are expensive, so we don't wanna lose time and, and usually contains bottles and we have about ten kilogram in the lab right now.

• 30:16Speaker 06

  So I'm the host from Columbia University. Currently I'm working on the xenon time experiment, uh which is.

• 30:24Speaker 06

  Yeah, so I'm working on the xenon time experiments, uh which is a dark matter direct detection experiment. Uh, it's located deep underground at L N G S in Italy. So our experiment has a lot of subsystem, but the core of the system is a, a so-called dual face liquid xenon time protection, time projection chamber. Or the T P C. So you know, when the particle gas scatters inside the T P C uh with the xenon atom, it can generate both simulations and ionizations. So the simulations with the prompt simulations can be detected by the top and bottom P M T arrays.

• 31:03Speaker 06

  Uh, in this silicon is silicon P M. Uh, the prompt simulation can be detected as a so-called S one. And we also have a pied drift field, so the ionized, ionized electrons will drift upwards and reach to the liquid gas interface and finally be detected as S two. So from S one, S two, we know quite a lot of information like. We can reconstruct the events uh positions. We know the uh energy, we buy the S one, S two. And but the most important as a professor question just said, we need to discriminate our signals from the background.

• 31:43Speaker 06

  And in the WIMP search, the dominant background is from the beta decays or the gamma from the materials. So these uh background events are so-called nuclear uh electronic recoil events. And because WIMP is expected to be electronic uh neutral. So it it should be the expected to be nuclear recoil events. So the key of the Zin Anton experiment is to discriminate electronic recoil events from the uh nuclear recoil events. And for these two different types of events uh where the recoils, their S one, S two ratio are different.

• 32:25Speaker 06

  And this brings a lot of power to discriminate our see uh to discriminate the signals from the background. And S one and S two, that's the self indirect or what, can you explain what S one and S two mean in this context? Yes, so the S two uh S one, S two mainly means, so in our analysis, it mainly means the size of the pulse. So you know, the S one, S two are both singulations, but the S two singulation is from the proportional uh. Yeah, so from the drifted electrons and it's proportional to the number of electrons. But anyways, these are both photons and be detected by the PMTs. And you have the waveforms from the PMTs.

• 33:05Speaker 06

  So in our analysis, the S one, S two usually means the size or the integrated area of this uh pulses.

• 33:13Speaker 02

  For example, our primary goal is to observe the uh WIMP dark matter and their signal is large, relatively large than the neutrino interactions. And without this trigon system, we might not be able to observe those very low signal, very low energy signals. Or uh the S two, S two only analysis or S one only analysis um without this trigon um.

• 33:35Speaker 06

  You can just take a, you know, a look at here, um. I imagine.

• 33:41Speaker 03

  Um, this is a so-called radon, radon reduced cleaning room. That would be for the uh for building the next generation experiment. So as I mentioned, radon is one of the dominant background for us. And for any low background dark matter or neutrino experiment. And the radons continue emitting from emanating from the materials, right? And so we want to make sure all the material put in to our detector. He um very much control internal radon emanation. So this especially be a clean room. And you see inside the oil, you know, uh metal coated and make sure the end of rail does.

• 34:26Speaker 03

  And even the hair, um, you know, even in our normal air, there are radons, right? So we have special um radon.

• 34:40Speaker 03

  Radium removal system, if you want to take a picture here. Um, this we inherited from an experiment called the XO two hundred. Um, a a neutrinoless double beta decay experiment that's you know, measure neutrino uh myrona particles. And so this is now is retired and we use it to clean the air here. And then pump the radon, remove the air into the clean. Into the clean. Yeah, yeah, so this is Professor Liang Yang's lab. Okay. Yeah, give me a quick tour. I know. And we'll see her around, yeah. He. I'll get him next time. Yeah, this um he's building some electronic radar.

• 35:22Speaker 02

  Sometimes you can beat swords into plowshares. We're about to see how the search for cosmic mysteries leads to very earthly applications, benefits, and truly hope for us to wage peace. The Pentagon looked at this dark matter detection technology and saw something else entirely, a way to monitor nuclear reactors from a distance, to verify treaty compliance without ever setting foot inside a facility. This is how basic research, fundamental research, can pay unexpected dividends. It's what happened in my field, the cosmic microwave background. We're building sensitive detectors to explore the wispy radiation from the Big Bang, eventually led to advancements in cellphone communications technology.

• 36:09Speaker 02

  Professor Ni's project is funded by DARPA, the same agency that gave us the Internet. We all know what a benefit that's been. This has a different type of benefit, one perhaps to help us seek peaceful resolutions to potential nuclear conflict.

• 36:24Speaker 03

  This is the apparatus actually we are building. And we call it neutrino detection with xenon. And we know the xenon detector now detect the solar neutrinos, right? We want to use this detector technology for some application, for example, detecting neutrino from reactors. We can monitor the reactor few, you know, remotely, not very far, 10, 20 meters away. And the detector is set up like here. Let me just open this.

• 36:59Speaker 03

  So the principle is very much the same as a dark matter detector. You build a cryogenic system, you have a detector vessel, and you have calibrations and trying to, you know, purify the xenon, more or less the same. Just, you know, eventually want to contain less than 100 kilograms xenon here, placed very close to a reactor core. And then we start to see a lot of reacting neutrinos.

• 37:25Speaker 02

  Could you use this for like weapons detection or trees violation of nuclear, you know, proliferation?

• 37:32Speaker 03

  That's the main purpose. Like you want to measure the component few in the nuclear reactors, you know, not, you know, from using neutrinos and to see the compositions, making sure the component inside is not changed during some down period. Yeah, that's the eventual goal.

• 37:56Speaker 02

  So is this funded by G O E or?

• 37:58Speaker 03

  It's a DARPA program. Yeah, but yeah, I had a three-year program and yeah, we built this setup for, yeah.

• 38:07Speaker 02

  So let me just, can I cut through?

• 38:09Speaker 03

  Yeah.

• 38:14Speaker 02

  So there's 100 liters, this one?

• 38:16Speaker 03

  Eventually, like 100 kilograms, we usually say 100 kilograms mass, yeah. And more or less this system is, yeah, we built, you know, based on the dark matter detector technology. Yeah, and.

• 38:35Speaker 03

  And so what is your... Is this his thesis or later? No, no, he is from Columbia. He's a visiting student. Yeah, this is actually my former student postdoc helping to build this system. And he already left, got a professor in somewhere else. And now students are working using this setup actually to build something useful for neutrinos. Wow, there you go. Yeah. There you go, very nice.

• 39:07Speaker 02

  Here's what we've learned today. For 30 years, one experiment has claimed to detect dark matter. For 30 years, increasingly sophisticated detectors have failed to confirm the Donald Lieber claim. We've seen technology so precise, it can catch neutrinos from the sun and witness rare nuclear decays that on average take longer than the age of our universe. But dark matter itself, well, it's still invisible, still undetected, still undefeated, still the greatest mystery in modern cosmology. Eighty-five percent of the universe is missing or made of something we've never seen. That should be humbling, but it should also thrill you because if most of reality is still hidden,

• 39:51Speaker 02

  imagine what else we can discover. If you want to see this technology in action and detail, check out the documentary on Professor Keating's experiments channel. Links in the description or click here. The search for dark matter isn't just about finding particles. It's about building the tools that reveal the invisible architecture of reality itself. And that search, well, my friends, that's just beginning.

• 40:22Speaker 00

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• 40:52Speaker 00

  When everyone's finally together, what makes mornings even brighter? Keeping things deliciously simple. Whether you're pouring up a

• 41:01Speaker 02

  Glass of morning refreshment, or topping off festive drinks for a family brunch, Simply Orange brings that 100% fresh squeezed taste to every moment. Deliciously bright and delightfully easy, Simply Orange is made for all your seasonal gatherings. Simply Orange, say yes to simple.