Latest / The Last Observer: Science and Beyond / A Single Recoil in the Mine: Dark Matter’s Most Intriguing Maybe

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A Single Recoil in the Mine: Dark Matter’s Most Intriguing Maybe · The Last Observer: Science and Beyond

• 0:00
  Speaker 1: Welcome to the Last Observer podcast. Today we will talk
• 0:03
  Speaker 1: about a possible first glimpse of dark matter from the
• 0:06
  Speaker 1: Lux Zeppelin experiment. A single unexplained particle hit a mile
• 0:11
  Speaker 1: underground in South Dakota.
• 0:13
  Speaker 2: Okay, I need you to say that again slowly. Dark matter.
• 0:17
  Speaker 2: The thing that is supposed to make up most of
• 0:19
  Speaker 2: the mass in the universe. And they think they might
• 0:22
  Speaker 2: have actually seen it?
• 0:24
  Speaker 1: They are not claiming they saw it. That is the
• 0:26
  Speaker 1: important part. They saw one event that does not look
• 0:29
  Speaker 1: like any of the usual background junk. It sits in
• 0:32
  Speaker 1: the exact region where a certain kind of dark matter
• 0:35
  Speaker 1: particle would land.
• 0:37
  Speaker 2: One event. That feels like finding a single footprint in
• 0:40
  Speaker 2: a desert and wondering if a person walked there.
• 0:43
  Speaker 1: Exactly. And physicists are trained to be allergic to one-off footprints.
• 0:48
  Speaker 1: 5 sigma is the gold standard for a discovery. This
• 0:51
  Speaker 1: is 2.6 sigma. Roughly a half percent chance it is
• 0:55
  Speaker 1: just some rare background they have not catalogued yet.
• 0:58
  Speaker 2: Half a percent is not nothing. That is not a
• 1:01
  Speaker 2: coin flip. That is the kind of number that makes
• 1:04
  Speaker 2: a room of particle physicists sit up a little straighter.
• 1:07
  Speaker 1: They presented it today, September 1st, at a conference in Japan.
• 1:12
  Speaker 1: The Lux Zeppelin Collaboration. 250 people from 39 institutions. The
• 1:18
  Speaker 1: detector lives in an old gold mine, almost a mile down,
• 1:22
  Speaker 1: so cosmic rays cannot fake the signal.
• 1:25
  Speaker 2: I love that. We hide from the sky to look
• 1:27
  Speaker 2: for the invisible stuff that holds galaxies together.
• 1:31
  Speaker 1: The tank holds 10 tons of liquid xenon, ultra-pure. When
• 1:35
  Speaker 1: something slams into a xenon nucleus, you get a tiny
• 1:39
  Speaker 1: flash of light, then electrons drift up and make a
• 1:42
  Speaker 1: second flash. Two signals. That pairing is how they tell
• 1:46
  Speaker 1: a nuclear recoil from random radioactive noise.
• 1:49
  Speaker 2: So this event had both flashes, and the ratio looked
• 1:53
  Speaker 2: like a nucleus getting kicked. not an electron getting tickled.
• 1:57
  Speaker 1: Yes, and it was a hard kick. If this is
• 2:00
  Speaker 1: a WIMP, a weakly interacting massive particle, it would be
• 2:04
  Speaker 1: at least 200 times heavier than a proton. That is
• 2:07
  Speaker 1: not the lightweight stuff a lot of earlier searches were
• 2:10
  Speaker 1: optimized for.
• 2:11
  Speaker 2: Wait, they already looked at this same data for the
• 2:14
  Speaker 2: classic low-energy WIMP bump and found nothing. Now they opened
• 2:18
  Speaker 2: a higher-energy window and one lonely event popped out.
• 2:22
  Speaker 1: That is the twist. The simplest elastic WIMP would have
• 2:25
  Speaker 1: left a trail of smaller recoils too. They did not
• 2:28
  Speaker 1: see that trail. So if this is dark matter, it
• 2:31
  Speaker 1: is not the textbook version. Maybe inelastic scattering. The particle
• 2:36
  Speaker 1: has to jump to a higher internal energy state, so
• 2:39
  Speaker 1: only high energy collisions count.
• 2:41
  Speaker 2: That would also explain why it showed up in June.
• 2:44
  Speaker 2: Earth is slamming into the galactic dark matter wind in summer.
• 2:48
  Speaker 2: Higher relative speed, more chance of clearing that energy threshold.
• 2:52
  Speaker 1: Theorists are already saying they do not have to invent
• 2:55
  Speaker 1: a whole new particle zoo for this. There are models
• 2:58
  Speaker 1: on the shelf that could produce exactly one punchy event
• 3:01
  Speaker 1: and not a smear of little ones.
• 3:04
  Speaker 2: Higher relative speed, more chance of clearing that energy threshold.
• 3:08
  Speaker 2: I am trying not to get carried away. Dark matter
• 3:11
  Speaker 2: experiments have teased us before. Xenon-1T had a bump that
• 3:15
  Speaker 2: vanished when the next detector looked harder.
• 3:19
  Speaker 1: The collaboration knows that history. Rick Gateskell, the spokesperson, said
• 3:24
  Speaker 1: they do not want to get ahead of themselves. They
• 3:26
  Speaker 1: just want other people to look at this event and
• 3:29
  Speaker 1: tell them if they missed a weird background.
• 3:31
  Speaker 2: Fair, but also, we have been circling this stuff for decades.
• 3:35
  Speaker 2: Gravity says it is there, galaxies spin too fast, light
• 3:39
  Speaker 2: bends too much, clusters hold together, and ordinary atoms cannot
• 3:44
  Speaker 2: account for it.
• 3:46
  Speaker 1: 85% of the mass in the universe, if the picture
• 3:48
  Speaker 1: is right, and it does not emit light. does not
• 3:51
  Speaker 1: absorb light, barely talks to us at all. The only
• 3:55
  Speaker 1: conversation it wants is gravity, and very rarely a bump
• 3:58
  Speaker 1: into a nucleus.
• 4:00
  Speaker 2: Clusters hold together, and ordinary atoms cannot account for it.
• 4:04
  Speaker 2: A mile underground, in a tank of frozen noble gas,
• 4:08
  Speaker 2: one nucleus flinched, and now half the field is staring
• 4:12
  Speaker 2: at that flinch.
• 4:14
  Speaker 1: They already have three times more data sitting on disk
• 4:17
  Speaker 1: that has not been run through this particular high energy search.
• 4:20
  Speaker 1: If this was real, there should be more footprints in
• 4:23
  Speaker 1: the next batch.
• 4:24
  Speaker 2: That is the test. One event is a rumor. A
• 4:27
  Speaker 2: handful is a story. Five Sigma is a headline that
• 4:31
  Speaker 2: rewrites textbooks.
• 4:33
  Speaker 1: Until then, we sit with the strangeness. A possible particle
• 4:36
  Speaker 1: 200 proton masses heavy arriving from the dark halo of
• 4:40
  Speaker 1: the Milky Way, tapping xenon like a ghost knocking once
• 4:44
  Speaker 1: on a door.
• 4:45
  Speaker 2: I keep thinking about how quiet that lab must be.
• 4:48
  Speaker 2: Rock all around, water shield. outer veto detectors hunting neutrons,
• 4:53
  Speaker 2: and still, something got through the filters and refused to
• 4:56
  Speaker 2: look like anything they know.
• 4:57
  Speaker 1: Aaron Manalasi from Berkeley Lab said this is the first
• 5:02
  Speaker 1: outlier he has seen that looks valid in every way.
• 5:05
  Speaker 1: Usually you stare at an odd event and it falls apart.
• 5:09
  Speaker 1: This one did not fall apart.
• 5:11
  Speaker 2: That sentence is going to live in my head, valid
• 5:14
  Speaker 2: in every way, and still they wait.
• 5:17
  Speaker 1: That is the discipline. The universe does not owe us
• 5:20
  Speaker 1: a clean announcement. Sometimes it leaves one mark and walks away.
• 5:24
  Speaker 2: All right, walk me through how they even know the
• 5:27
  Speaker 2: background is that low. Because if the background estimate is wrong,
• 5:31
  Speaker 2: the half percent evaporates.
• 5:33
  Speaker 1: The background story is almost as impressive as the possible signal.
• 5:37
  Speaker 1: They do not just hope the mine is quiet. They
• 5:39
  Speaker 1: measure every way ordinary matter can fake a dark matter kick.
• 5:44
  Speaker 2: Cosmic rays first. Those are the easy ones. A mile
• 5:48
  Speaker 2: of rock knocks them down to almost nothing.
• 5:51
  Speaker 1: Then neutrons from the rock and from the detector materials.
• 5:54
  Speaker 1: Neutrons can smack a xenon nucleus and look a lot
• 5:57
  Speaker 1: like a wimp. So they wrap the inner tank in
• 6:00
  Speaker 1: a veto system. If something happens in the outer detectors
• 6:03
  Speaker 1: at the same time, they throw the event away.
• 6:06
  Speaker 2: And radioactivity in the xenon itself. Even ultra-pure xenon has
• 6:11
  Speaker 2: traces of krypton and radon daughters. Those decay and make flashes.
• 6:16
  Speaker 1: The two-flash trick helps. An electron recoil from a gamma
• 6:20
  Speaker 1: or a beta decay makes a different ratio of prompt
• 6:23
  Speaker 1: light to drifted electrons than a nuclear recoil. They draw
• 6:27
  Speaker 1: a band on a plot. Radioactivity lives on one curve.
• 6:31
  Speaker 1: Nuclear kicks live on another.
• 6:33
  Speaker 2: And this lone event sat off the radioactivity curve in
• 6:36
  Speaker 2: the nuclear recoil region at high energy, where they expected
• 6:40
  Speaker 2: almost zero background.
• 6:43
  Speaker 1: Sam Erickson... who led the analysis at Bristol, said they
• 6:46
  Speaker 1: spent months extra just trying to invent a background that
• 6:49
  Speaker 1: could land there. They understand the detector well enough that
• 6:53
  Speaker 1: a single leftover event matters.
• 6:55
  Speaker 2: I like that honesty. We expected dark matter to be rare,
• 6:59
  Speaker 2: so a handful of events could already be the first detection.
• 7:03
  Speaker 2: They are not waiting for a flood.
• 7:05
  Speaker 1: The dataset was 220 live days from March 2023 to
• 7:07
  Speaker 1: April 2024. They had already published a search in the
• 7:14
  Speaker 1: low-energy window on that same exposure and set world-leading limits.
• 7:19
  Speaker 1: This was a second pass, looking for punchier recoils.
• 7:23
  Speaker 2: So they are not changing the rules after seeing the data.
• 7:26
  Speaker 2: They opened a window they had not fully used, and
• 7:29
  Speaker 2: one event was sitting in it.
• 7:31
  Speaker 1: The event even has a name in the notes.
• 7:33
  Speaker 2: LZ230616.
• 7:34
  Speaker 1: June 16, 2023. Midsummer. That date is not proof of anything.
• 7:42
  Speaker 1: But if inelastic dark matter is real, summer is when
• 7:45
  Speaker 1: you expect the energetic collisions.
• 7:48
  Speaker 2: The Earth is moving around the Sun, and the Sun
• 7:51
  Speaker 2: is moving through the galaxy. For part of the year
• 7:54
  Speaker 2: we fly into the dark matter wind. Relative speed goes up.
• 7:58
  Speaker 2: Threshold interactions become more likely.
• 8:01
  Speaker 1: Classic wimp searches also look for that annual modulation. Dharma
• 8:05
  Speaker 1: claimed it for years, and nobody else reproduced it cleanly.
• 8:09
  Speaker 1: So people are wary of season arguments. It is a
• 8:13
  Speaker 1: nice consistency check if more events show up and they
• 8:16
  Speaker 1: cluster in summer.
• 8:18
  Speaker 2: What would a 200 GeV WIMP even mean for the
• 8:21
  Speaker 2: early universe? That is a heavy particle. Thermal freeze-out at
• 8:26
  Speaker 2: that mass is tight. You need the right annihilation rate
• 8:29
  Speaker 2: or you overproduce it.
• 8:31
  Speaker 1: There are ways. Co-annihilation, a slightly heavier partner that helps
• 8:36
  Speaker 1: burn it down, or the particle was never in thermal
• 8:39
  Speaker 1: equilibrium and got made by some other process. Theorists have
• 8:43
  Speaker 1: been writing those papers for 20 years waiting for a
• 8:46
  Speaker 1: hint like this.
• 8:48
  Speaker 2: Gigi Phan at Brown, who was not on the experiment,
• 8:51
  Speaker 2: said there are well-motivated extensions. Inelastic scattering. Momentum-dependent elastic scattering.
• 8:58
  Speaker 2: You do not have to throw the wimp idea in
• 9:00
  Speaker 2: the trash. You just stop assuming the simplest collision.
• 9:04
  Speaker 1: That is why this feels different from a random bump.
• 9:07
  Speaker 1: It is odd, but it is odd in a direction
• 9:10
  Speaker 1: theory already pointed.
• 9:12
  Speaker 2: Meanwhile, the detector keeps running. They have the largest dark
• 9:15
  Speaker 2: matter exposure on Earth right now, and it is still growing.
• 9:19
  Speaker 2: More live days means either this event becomes a lonely
• 9:22
  Speaker 2: fluke or friends appear.
• 9:25
  Speaker 1: Other xenon experiments will look too. Xenon-T in Italy, Panda-X
• 9:30
  Speaker 1: in China. If nature put a heavy inelastic wimp in
• 9:34
  Speaker 1: the halo, they should eventually see the same kind of
• 9:37
  Speaker 1: isolated hard recoil.
• 9:39
  Speaker 2: And if they do not, Then LZ either got unlucky
• 9:42
  Speaker 2: with a 1 in 200 background, or they found a
• 9:44
  Speaker 2: new rare process that is not dark matter at all.
• 9:48
  Speaker 2: That would still be interesting. A background nobody modeled is
• 9:51
  Speaker 2: a physics result.
• 9:53
  Speaker 1: Particle physics has a habit of discovering the thing next
• 9:56
  Speaker 1: to the thing you wanted. Neutrinos were a headache before
• 9:59
  Speaker 1: they were a fear. This could be a headache that
• 10:01
  Speaker 1: becomes a field.
• 10:03
  Speaker 2: I keep coming back to the human scale of it.
• 10:06
  Speaker 2: Graduate students at Brown watching the live display. Machine learning
• 10:10
  Speaker 2: tools they built to clean the data. Undergraduates writing code
• 10:13
  Speaker 2: that helps decide whether a flash is real.
• 10:16
  Speaker 1: Science at this level is not a lone genius in
• 10:19
  Speaker 1: a cave. It is a small city of people arguing
• 10:22
  Speaker 1: about one blip on a plot.
• 10:24
  Speaker 2: And the plot is public now. Paper going to physical
• 10:27
  Speaker 2: review letters. Talk slides out. The community can try to
• 10:31
  Speaker 2: break it.
• 10:32
  Speaker 1: That is how you know they are serious. They did
• 10:35
  Speaker 1: not sit on it until they had five events. They
• 10:38
  Speaker 1: showed the one event and asked for help.
• 10:40
  Speaker 2: If I were a theorist tonight, I would be running scams.
• 10:44
  Speaker 2: What mass splitting in an inelastic model fits one high-energy
• 10:48
  Speaker 2: recoil and zero low-energy recoils in 220 days.
• 10:53
  Speaker 1: And if I were on a competing experiment, I would
• 10:56
  Speaker 1: be unblinding the same energy window as fast as the
• 10:59
  Speaker 1: collaboration rules allow.
• 11:01
  Speaker 2: The quiet part is that even if this fades, the
• 11:04
  Speaker 2: machine worked. They can see a single nuclear recoil in
• 11:07
  Speaker 2: 10 tons of xenon and not lose it in the noise.
• 11:11
  Speaker 2: That capability is new in this energy range.
• 11:15
  Speaker 1: Neil Weiner at NYU said, That is the top line,
• 11:19
  Speaker 1: even before you decide what the event is. These detectors
• 11:23
  Speaker 1: can hunt a broader set of stories than the original
• 11:25
  Speaker 1: WIMP cartoon.
• 11:26
  Speaker 2: The cartoon was a particle that bounced like a billiard
• 11:29
  Speaker 2: ball and left a soft trail. The real world might
• 11:32
  Speaker 2: be pickier. Energy thresholds, internal states, velocity dependence.
• 11:38
  Speaker 1: Nature does not owe us the simplest Lagrangian. It only
• 11:41
  Speaker 1: owes us consistency with what we already measured.
• 11:45
  Speaker 2: Which brings us to why we believe dark matter exists
• 11:48
  Speaker 2: at all, even after all these null searches.
• 11:51
  Speaker 1: Start with rotation curves. Stars on the outskirts of spiral
• 11:55
  Speaker 1: galaxies move too fast. If you only count the stars
• 11:59
  Speaker 1: and gas you can see, those outer stars should drift away.
• 12:02
  Speaker 1: They do not.
• 12:03
  Speaker 2: So something extra is holding them. A halo of mass
• 12:07
  Speaker 2: that does not shine.
• 12:09
  Speaker 1: Then, gravitational lensing. Clusters of galaxies bend light more than
• 12:13
  Speaker 1: their visible mass allows. The bullet cluster is the famous picture.
• 12:17
  Speaker 1: Two clusters collided. The hot gas slammed and stopped, but
• 12:21
  Speaker 1: the bulk of the mass kept going. The mass was
• 12:24
  Speaker 1: not in the gas. It was in something that barely interacted.
• 12:27
  Speaker 2: That is hard to fake with modified gravity. You can
• 12:30
  Speaker 2: tweak gravity in a quiet galaxy. It is harder when
• 12:34
  Speaker 2: two systems smash and the mass and the light go
• 12:37
  Speaker 2: different ways.
• 12:38
  Speaker 1: Cosmic microwave background 2. The pattern of hot and cold
• 12:42
  Speaker 1: spots in the infant universe... fits a universe that is
• 12:45
  Speaker 1: about 5% ordinary matter, 25% dark matter, and the rest
• 12:50
  Speaker 1: dark energy. Change those fractions and the peaks in the
• 12:54
  Speaker 1: power spectrum move.
• 12:55
  Speaker 2: So we are not hunting a rumor. We are hunting
• 12:58
  Speaker 2: a substance whose gravity is measured three different ways. We
• 13:02
  Speaker 2: just do not know the particle.
• 13:04
  Speaker 1: Wimps were the favorite because they appear almost for free
• 13:08
  Speaker 1: in supersymmetry, a stable heavy particle that froze out with
• 13:12
  Speaker 1: roughly the right density. beautiful. Then the Large Hadron Collider
• 13:16
  Speaker 1: did not hand us superpartners, and the xenon tanks did
• 13:19
  Speaker 1: not light up in the easy window.
• 13:21
  Speaker 2: So the field widened. Axions, sterile neutrinos, primordial black holes,
• 13:27
  Speaker 2: fuzzy dark matter, dark photons, whole hidden sectors.
• 13:33
  Speaker 1: LZ is built for WIMPs, especially in the tens to
• 13:36
  Speaker 1: hundreds of GeV range. An event at 200 GeV, if real,
• 13:41
  Speaker 1: would pull some of those other ideas back toward the
• 13:44
  Speaker 1: sidelines and put a heavy, weakly interacting particle back on
• 13:47
  Speaker 1: the table.
• 13:48
  Speaker 2: Not the simplest wimp. A cousin, still in the family.
• 13:53
  Speaker 1: There is also the neutrino fog. These detectors are now
• 13:56
  Speaker 1: so sensitive that solar neutrinos bounce off xenon nuclei through
• 14:00
  Speaker 1: coherent scattering. That is a standard model process. It looks
• 14:04
  Speaker 1: a bit like light-dark matter. LZ and ZenONT have both
• 14:08
  Speaker 1: seen that fog.
• 14:10
  Speaker 2: Which is wild. The same machine that hunts the unknown
• 14:13
  Speaker 2: is now a neutrino observatory. But that fog sits at
• 14:17
  Speaker 2: low energy. This new event is higher. Different neighborhood on
• 14:21
  Speaker 2: the plot. Good.
• 14:23
  Speaker 1: You do not want your maybe wimp sitting where boron-8
• 14:26
  Speaker 1: neutrinos live. That would be an easy way to fool yourself.
• 14:30
  Speaker 2: History is full of almosts. Dama modulation. Cogent excess. CDMS
• 14:36
  Speaker 2: silicon events. Xenon-1T electron excess. Each one taught the field
• 14:42
  Speaker 2: how to be meaner about systematics.
• 14:45
  Speaker 1: That meanness is a feature. If this event survives the
• 14:48
  Speaker 1: next year of scrutiny, it will have earned it.
• 14:51
  Speaker 2: What would change if it is real? Not your grocery list,
• 14:54
  Speaker 2: but cosmology models get a particle mass to plug in.
• 14:58
  Speaker 2: Direct detection roadmaps shift. Collider searches get a target mass.
• 15:03
  Speaker 2: Indirect detection, looking for annihilation gamma rays in the galactic center,
• 15:08
  Speaker 2: gets a new benchmark.
• 15:10
  Speaker 1: And philosophy of the universe shifts a millimeter. We would
• 15:13
  Speaker 1: have touched the dominant form of matter for the first time,
• 15:16
  Speaker 1: not inferred it, touched it. One nucleus in South Dakota
• 15:21
  Speaker 1: recoiled because the halo of the Milky Way brushed it.
• 15:24
  Speaker 2: That sentence should not be allowed to sound ordinary.
• 15:28
  Speaker 1: It does not. I can feel the scale mismatch. A
• 15:31
  Speaker 1: particle that may have been born in the first second
• 15:34
  Speaker 1: after the Big Bang, circling with the galaxy for 13
• 15:37
  Speaker 1: billion years. And then one Tuesday in June, it hits
• 15:40
  Speaker 1: a xenon atom we purified and poured into a tank.
• 15:44
  Speaker 2: Or it was radon. Or a neutron that slipped the veto.
• 15:48
  Speaker 2: Or a software ghost. That is the other door. And
• 15:51
  Speaker 2: it is still wide open.
• 15:52
  Speaker 1: 2.6 sigma means both doors are open. Discovery door. Embarrassment door.
• 15:59
  Speaker 1: The experimenters chose to walk into the hallway and tell
• 16:02
  Speaker 1: everyone there are two doors.
• 16:04
  Speaker 2: I respect that more than a hype press release. The
• 16:07
  Speaker 2: temptation to wait for more data must have been huge.
• 16:10
  Speaker 1: Waiting has a cost too. Other groups cannot cross-check a secret.
• 16:15
  Speaker 1: Theory cannot aim, so they publish the rumor with the
• 16:18
  Speaker 1: error bars attached.
• 16:19
  Speaker 2: The detector itself is a kind of sculpture. Photomultiplier tubes
• 16:24
  Speaker 2: like golden eyes on the top and bottom. An electric
• 16:27
  Speaker 2: field dragging electrons upward through liquid xenon so cold it
• 16:31
  Speaker 2: is a dense, clear fluid.
• 16:33
  Speaker 1: Brown built a lot of those light sensors. Students who
• 16:36
  Speaker 1: will be professors someday can say they helped assemble the
• 16:39
  Speaker 1: eyes that maybe saw the dark.
• 16:41
  Speaker 2: There is a future experiment on the drawing board called XLZD. Xenon, LZ,
• 16:48
  Speaker 2: and Darwin merging into a bigger tank. 60 to 80
• 16:52
  Speaker 2: tons of active xenon. If this hint is real, that
• 16:55
  Speaker 2: machine would turn a rumor into a spectrum.
• 16:59
  Speaker 1: A spectrum. Not one event. An energy shape. A rate
• 17:03
  Speaker 1: versus time. Maybe a direction if they get clever. That
• 17:07
  Speaker 1: is when you stop whispering maybe.
• 17:09
  Speaker 2: Until then, we live in the maybe, which, honestly, is
• 17:12
  Speaker 2: the most interesting room in science.
• 17:15
  Speaker 1: The maybe room is where you still get to be surprised.
• 17:18
  Speaker 2: Walk through what happens next in practical terms. Who looks,
• 17:23
  Speaker 2: how long, what would kill the idea?
• 17:25
  Speaker 1: First, LZ analyzes the extra live time they already have.
• 17:30
  Speaker 1: Three times the exposure. maybe more by the time the
• 17:33
  Speaker 1: next paper lands. If the rate is real, you expect
• 17:37
  Speaker 1: a few more isolated hard recoils. If the rate is
• 17:40
  Speaker 1: a fluke, the new data stay empty in that corner
• 17:43
  Speaker 1: of the plot.
• 17:44
  Speaker 2: Empty would not prove the first event was fake. Rare
• 17:49
  Speaker 2: backgrounds happen once, but empty would make the story much
• 17:53
  Speaker 2: less urgent.
• 17:54
  Speaker 1: Second, independent xenon tanks. Different mine, different materials, different analysis teams.
• 18:01
  Speaker 1: a matching event in Italy or China would be huge.
• 18:05
  Speaker 1: A hard veto from those detectors would sting.
• 18:08
  Speaker 2: Third, theory papers. They will map the mass and the splitting.
• 18:13
  Speaker 2: They will ask whether such a particle overcloses the universe,
• 18:17
  Speaker 2: or underproduces, or messes up the cosmic microwave background.
• 18:21
  Speaker 1: Fourth, collider people will ask whether a 200 GeV weekly
• 18:26
  Speaker 1: interacting state should have shown up at the LHC already.
• 18:30
  Speaker 1: Sometimes the answer is no, because the production mode is sneaky.
• 18:34
  Speaker 1: Sometimes the answer is, we should have seen a hint
• 18:37
  Speaker 1: and did not, which puts pressure on the model.
• 18:41
  Speaker 2: And fifth, the quiet work. Recalibrate the veto. Revisit neutron yields.
• 18:47
  Speaker 2: Hunt for a software coincidence that only happens once in
• 18:50
  Speaker 2: 200 days. That unglamorous stuff is how you earn trust.
• 18:55
  Speaker 1: Wick Haxton called it the most interesting thing in recent times.
• 18:58
  Speaker 1: and said there will be a flood of people looking
• 19:00
  Speaker 1: at this event. That is the healthiest possible reaction, not celebration, attention.
• 19:08
  Speaker 2: Dan Hooper said it is only one event, who knows,
• 19:11
  Speaker 2: and also that it is intriguing. Both halves of that
• 19:15
  Speaker 2: sentence are true at once.
• 19:17
  Speaker 1: I keep picturing the control room when they unblinded that
• 19:20
  Speaker 1: high-energy box. You write the cuts, you freeze the rules,
• 19:24
  Speaker 1: you open the box. And there is one point sitting
• 19:27
  Speaker 1: where the map said almost nothing should live.
• 19:31
  Speaker 2: Someone probably said a word you cannot put on a podcast.
• 19:34
  Speaker 1: Then they did the adult thing. They tried for months
• 19:38
  Speaker 1: to kill their own event. They failed to kill it.
• 19:41
  Speaker 1: So they told the world.
• 19:43
  Speaker 2: That is a good definition of scientific courage. Not shouting eureka,
• 19:48
  Speaker 2: refusing to hide the maybe.
• 19:50
  Speaker 1: Dark matter has been a gravitational silhouette for almost a century,
• 19:54
  Speaker 1: depending how you count. Zwicky with clusters, Rubin with rotation curves,
• 20:00
  Speaker 1: then the microwave sky, then lensing maps. Direct detection was
• 20:04
  Speaker 1: supposed to put a face on the silhouette.
• 20:07
  Speaker 2: Today we might have a single pixel of that face. Blurry. Contested. Precious.
• 20:14
  Speaker 1: Or we have a pixel of something else we do
• 20:16
  Speaker 1: not understand yet, which is also a gift. Unknown backgrounds
• 20:20
  Speaker 1: are how new physics sneaks in wearing work clothes.
• 20:24
  Speaker 2: Either way, the universe just became slightly less abstract. There
• 20:28
  Speaker 2: is a tank in a mine and a date on
• 20:30
  Speaker 2: a plot and a mass estimate written in pencil.
• 20:33
  Speaker 1: 200 times a proton. June. South Dakota. Liquid xenon. Two flashes.
• 20:41
  Speaker 1: One leftover point.
• 20:43
  Speaker 2: I am going to be checking for the follow-up analysis
• 20:46
  Speaker 2: the way some people check sports scores. That is a
• 20:49
  Speaker 2: strange hobby, and I accept it.
• 20:51
  Speaker 1: Same. If more events appear, I want to know the
• 20:55
  Speaker 1: season they arrived. I want to know the energy. I
• 20:58
  Speaker 1: want to know if the other experiments blink.
• 21:02
  Speaker 2: And if nothing appears, I want to know what rare
• 21:04
  Speaker 2: process they found instead. Because a detector this clean should
• 21:09
  Speaker 2: not have mystery recoils without a reason.
• 21:11
  Speaker 1: That is the pact. We built a quiet room under
• 21:14
  Speaker 1: a mountain so the universe would have fewer places to hide.
• 21:19
  Speaker 1: Now we wait to see what speaks in the quiet.
• 21:22
  Speaker 2: A mile of rock. Ten tons of xenon. Two hundred
• 21:27
  Speaker 2: and fifty people. One knock on the door.
• 21:30
  Speaker 1: Welcome to the Last Observer Podcast. We spent this hour
• 21:35
  Speaker 1: on a possible first glimpse of dark matter from Lux Zeppelin.
• 21:39
  Speaker 1: Not a discovery. A question with better lighting than usual.
• 21:43
  Speaker 2: Keep an eye on that mine. The halo of the
• 21:46
  Speaker 2: galaxy is still passing through us, whether we catch it
• 21:49
  Speaker 2: or not.
• 21:50
  Speaker 1: Every second, if the models are right, a river of
• 21:53
  Speaker 1: invisible particles streams through this room, through your hands, through
• 21:57
  Speaker 1: the Earth, and almost never stops to say hello.
• 22:01
  Speaker 2: Almost never. That is the whole game.
• 22:05
  Speaker 1: Thanks for listening. Stay curious. Stay skeptical. And if the
• 22:10
  Speaker 1: universe knocks again, we will be here.
• 22:13
  Speaker 2: We will be here.