> It's an open question, right, whether dark matter has no interaction or just very little interaction with normal matter? If there's none, this experiment will detect nothing but noise.
Correct. What this experiment (LUX-ZEPLIN) is looking for is the effects of xenon nuclei being "bumped" - recoiling - due to something undetectable. It doesn't matter what interaction mediates the recoil - it could even be a so-far-undiscovered interaction. They're just looking for evidence of the recoil happening. But if the only interaction is gravity, they won't detect anything, since gravity is too weak for us to detect the effects of at that scale.
> I'm confused why, if dark matter exists and has mass (since it interacts gravitationally), there's no noticeable missing results from high-energy events that create particles.
Particle physicists actively look for this, e.g. in reactions in particle accelerators. But not finding evidence of that only places constraints on how strongly dark matter can couple to ordinary matter, it doesn't rule it out.
> Shouldn't dark matter particles be generated by, say, cosmic ray collisions?
Not necessarily. Just being energetic doesn't guarantee anything. There's a bit of a chicken-and-egg issue here: without knowing more about dark matter, we can't predict what reactions might produce it. That's why experiments like LUX-ZEPLIN make as few assumptions as possible - all it requires is that some mechanism for energy transfer from dark matter to matter exists.
> Or black hole decay?
Black hole decay has never been observed. Since it's purely theoretical, no matter how well-justified it is, it doesn't really help in the search for dark matter. There's no reason that Hawking radiation couldn't include dark matter, in fact if dark matter exists it probably would, but we have no way to detect that.
Even if say black hole collisions (which have been indirectly observed) produced dark matter, we wouldn't really have any way of detecting it at the distances in question.
Correct. What this experiment (LUX-ZEPLIN) is looking for is the effects of xenon nuclei being "bumped" - recoiling - due to something undetectable. It doesn't matter what interaction mediates the recoil - it could even be a so-far-undiscovered interaction. They're just looking for evidence of the recoil happening. But if the only interaction is gravity, they won't detect anything, since gravity is too weak for us to detect the effects of at that scale.
> I'm confused why, if dark matter exists and has mass (since it interacts gravitationally), there's no noticeable missing results from high-energy events that create particles.
Particle physicists actively look for this, e.g. in reactions in particle accelerators. But not finding evidence of that only places constraints on how strongly dark matter can couple to ordinary matter, it doesn't rule it out.
> Shouldn't dark matter particles be generated by, say, cosmic ray collisions?
Not necessarily. Just being energetic doesn't guarantee anything. There's a bit of a chicken-and-egg issue here: without knowing more about dark matter, we can't predict what reactions might produce it. That's why experiments like LUX-ZEPLIN make as few assumptions as possible - all it requires is that some mechanism for energy transfer from dark matter to matter exists.
> Or black hole decay?
Black hole decay has never been observed. Since it's purely theoretical, no matter how well-justified it is, it doesn't really help in the search for dark matter. There's no reason that Hawking radiation couldn't include dark matter, in fact if dark matter exists it probably would, but we have no way to detect that.
Even if say black hole collisions (which have been indirectly observed) produced dark matter, we wouldn't really have any way of detecting it at the distances in question.