Searching for dark matter, deep in the Earth
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What is the main topic of the SuperCDMS SNOLAB experiment?
Hey, it's Flora, and you are listening to Science Friday. When I think about dark matter, my mind goes to outer space. I imagine, I don't know, I imagine mysterious cosmic dust bunnies floating around in the distant universe. But a lot of them, because we know dark matter makes up 80-something percent of the total matter of the universe. But researchers are looking for signs of dark matter right here on Earth. An experiment called Super CDMS is searching for the signatures of dark matter deep, deep underground. Here to tell us more is Dr. Priscilla Cushman. She's a physicist at the University of Minnesota and has been working on this dark matter hunting experiment for over 20 years.
Why is dark matter research conducted deep underground?
Priscilla, welcome to Science Friday. Thank you for inviting me. I love your show, by the way. Oh, thank you. Appreciate it. Also, welcome back to the surface of Earth.
Is dark matter present all around us right now?
I understand you've been deep below for a bit. I have. I have indeed. Should I picture you in a lab coat and a miner's helmet?
Well, the lab coat, no. You'll have to think more about a large miner's coverall and a utility belt and a backpack filled with not only my own stuff I need, but also a self-rescuer that weighs about 20 pounds, marching about a kilometer to get to the lab, actually, at two kilometers below the surface.
Wow. Why do you need to be so deep underground to do this research?
Well, basically, we have very, very sensitive detectors, right?
What specific interactions are researchers looking for with dark matter?
And so they're sensitive to everything. And that includes the cosmic rays, which are intersecting us and the Earth at all times. And they get blocked by the Earth between the surface and where the lab is. But the dark matter particles do not. because they are so weakly interacting. Basically, they pass through the earth. You would count as many of them at night as at day because they can just come through the other side of the earth any way they want.
This is something that I think upends one of my preconceived notions. So is dark matter everywhere? Is it in the room with us right now? At this very moment.
But it is moving quite fast because not so much that it is moving fast, but that we are moving fast through it as we move around the sun and as our solar system moves around our galaxy.
Is it staying still?
Why is cooling important for dark matter detection?
Is it floating there and we're moving through it?
Yeah, it's more to think of it that way, because the relative motion is all that counts, because we're having detectors that measure the kinetic energy of the particles. And so from our point of view, it's like this dark matter wind that's moving through our detectors. But only one in a trillion actually gets close enough to one of our target atoms to move the nucleus a tiny bit. And that's why we have a hard time seeing it, although there's so much of it.
Yeah, let's talk about that. What are you looking for exactly?
So what we're looking for is an interaction between a dark matter particle and a nucleus. Our target material, for example, are crystals of germanium or silicon. The target material exist to be interacted with, if you like. So we have all of this collection of nuclei and the dark matter particles are moving through and they have to be very close to the nucleus to make an interaction. But that's what we're looking for.
What milestones have been achieved in the SuperCDMS experiment?
Imagine that you are standing in the middle of a large stadium and then the nucleus would be like putting a little grape down in the middle, and all the electrons are out at the edges of that stadium. So for a dark matter particle that needs to get very, very close to that grape, there is a ton of open space for it to go through. And that's our main problem is that there's a lot of dark matter particles, but as they move through us and through the Earth, and also through our detectors, we have a hard time detecting them because they mostly just pass through. Obviously, the more detectors you have, the more nuclei you have, and the longer you wait to see an interaction, the more likely you are to see one.
So that's what drives the need for a larger and larger detector, or in our case, very sensitive detectors that can look at the very lowest and tiniest energy depositions.
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Chapters
8 chapters
1
What is the main topic of the SuperCDMS SNOLAB experiment?
0:04–0:50
2
Why is dark matter research conducted deep underground?
0:50–0:58
3
Is dark matter present all around us right now?
0:58–1:36
4
What specific interactions are researchers looking for with dark matter?
1:36–2:29
5
Why is cooling important for dark matter detection?
2:29–3:37
6
What milestones have been achieved in the SuperCDMS experiment?
3:37–4:49
7
What will the first data collection phase look like?
4:49–6:40
8
What are the implications of discovering dark matter particles?
6:40–14:29
Speakers
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