Record-Setting Dark Matter Detector Comes Up Empty -- and That's Good News (gizmodo.com) 42
An anonymous reader quotes a report from Gizmodo: WIMPs (weakly interacting massive particles) are one of the most serious contenders for dark matter -- the "missing" mass supposedly constituting 85% of our universe. Given its elusiveness, dark matter tests the patience and creativity of physicists. But the latest results from LUX-ZEPLIN (LZ), the South Dakota-based detector, may have brought scientists a small step closer to catching WIMPs in action. In a recent Physical Review Letters paper, scientists analyzed 280 days' worth of data from LUX-ZEPLIN, reporting the tightest ever upper limit on the interaction strength of WIMPs. The result -- a near fivefold improvement -- demonstrates how physicists are increasingly getting better at circumventing the problem that dark matter is, well, dark; the elusive stuff evades any detection method that depends on materials interacting with visible light or other types of radiation.
The LUX-ZEPLIN experiment, located one mile underground in a decommissioned South Dakota gold mine, employs nearly 15,000 pounds (7 tons) of liquid xenon. The chemical element's high atomic mass and density make it potentially easier for scientists to detect any unknown particles that may pass through the detector. Also, liquid xenon is transparent, preventing any unwanted noise -- usually arising from radioactive matter around the detector -- from spoiling an experiment. "These results firmly establish that LZ is the world's most sensitive search for dark matter heavier than 10 GeV, that's about 10 times heavier than a proton," explained Scott Haselschwart, a physicist at the University of Michigan and LZ physics coordinator, in an email to Gizmodo. "To put our result in perspective: we have ruled out dark matter that would interact only once in a single kilogram of xenon every four millennia!" "LZ is the most sensitive search for WIMP dark matter to date, but we still have another two years of data to collect," Haselschwart said. "This means that a discovery of dark matter in LZ could come anytime now. We are truly looking for dark matter where no one has ever looked before and that is extremely exciting!"
The LUX-ZEPLIN experiment, located one mile underground in a decommissioned South Dakota gold mine, employs nearly 15,000 pounds (7 tons) of liquid xenon. The chemical element's high atomic mass and density make it potentially easier for scientists to detect any unknown particles that may pass through the detector. Also, liquid xenon is transparent, preventing any unwanted noise -- usually arising from radioactive matter around the detector -- from spoiling an experiment. "These results firmly establish that LZ is the world's most sensitive search for dark matter heavier than 10 GeV, that's about 10 times heavier than a proton," explained Scott Haselschwart, a physicist at the University of Michigan and LZ physics coordinator, in an email to Gizmodo. "To put our result in perspective: we have ruled out dark matter that would interact only once in a single kilogram of xenon every four millennia!" "LZ is the most sensitive search for WIMP dark matter to date, but we still have another two years of data to collect," Haselschwart said. "This means that a discovery of dark matter in LZ could come anytime now. We are truly looking for dark matter where no one has ever looked before and that is extremely exciting!"
This has been going on for 100 years (Score:4, Interesting)
Re:This has been going on for 100 years (Score:5, Insightful)
The problem is: Where to?
We have no obvious path, and the ones proposed so far are even more elusive. Physicists would love to move on, and the ones leading a promising new way will be hailed as the Newtons and Einsteins of the 21st century. Currently, we are in the process to mark out all possible places to look, and we are crossing out the squares we have searched so far. Each square cleared is a success, because it narrows down the places to look even further.
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-Yes that is many questions, but it is better than ruling just on thing out each decade, is the current pace even that fast? Oops another question - we just don't have any answers. It's OK to admit this.
Re:This has been going on for 100 years (Score:4, Informative)
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Oops another question - we just don't have any answers. It's OK to admit this.
This is your alternative? Just give up?
Thankfully most scientists throughout history did not have your approach to science.
Alternative Models (Score:3)
We have no obvious path, and the ones proposed so far are even more elusive.
That's not really true. Axions - that solve the strong CP problem - are looking like an increasingly likely candidate for Dark Matter. LIGO can also test the hypothesis that Dark Matter is just small Black Holes - while the source of such BHs is not theoretically motivated it's not experimentally ruled out yet and if they were found we all know the theorists would come up with ideas of where they came from!
While you could argue that none of these are "obvious paths" with the death of the WIMP miracle I
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And LIGO can't test the small Black Holes hypothesis. It measures gravitational waves in the wrong frequency band. The lowest mass it can detect is about the size of a neutron star binary (~ 3 solar masses). Advanced LIGO will be able to detect masses down to a single neutron star (1.4 solar masses), still too large for the hypothetic small primordial Black Holes.
Re:Alternative Models (Score:4, Interesting)
LIGO goes after the intermediate BH masses - substellar size mergers are detectable with their projected upgrades at closer distances where there should be enough to mergers to detect close enough to see them if these are Dark Matter. As the mass drops, the number of BHs needed to explain DM increase and so the chances of a much closer-by merger increase.
The frequency is determined by the orbital period and for larger masses this is lower giving a shorter sensitivity period for really large mass BH mergers. Lower mass BHs would generate a detectable signal for longer but at lower amplitudes hence the need for increased sensitivity to see them - at least according the last talk I saw on this. While the mass range of BHs that are still not ruled out is not well theoretically motivated, I'd argue we should still cover since theorists are not always right. Small BHs under ~5 x 10^11 kg can be ruled out as Dark Matter since their lifetime is short enough that most would have decayed via Hawking Radiation within the age of the universe.
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Axions are as elusive as WIMPS - they are only hypothesized and not detected yet.
Elusive means "difficult to find, catch or achieve" hence, for something to be "elusive" it must exist and the degree of difficulty of the search for it determines the level of elusiveness. Being hypothetical does not make something elusive, you can hypothesize a very easy to detect particle but then your theory will not remain at the hypothesis stage for long since data will quickly confirm or deny it. Conversely, WIMPS have been hypothesized for decades and we have been searching for them for that long u
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Michelson-Morley (Score:3)
Negative results can sometimes be very profound...although for LUX that is not really the case. I would not describe this result as exciting but it is useful. To be exciting they would actually have to have found evidence of Dark Matt
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The problem is that we don't have a better theory than dark matter to explain the motion of galaxies, although MOND and its derivatives are a close second.
A good theory must explain all observations with the least amount of free parameters. And dark matter is actually quite good in that regard: we have stuff that is massive and that we currently can't detect except for its gravitational effect on galaxies, and a particle is currently the favorite candidate. I mean, why not, neutrinos were like that not so l
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Gee, I wonder why those silly scientists didn't ask you first before constructing the models and then the experiments to conduct to either validate or falsify them. You'd have been able to save them all those billions of dollars. Have you informed them that you have this skill? I am sure they'd listen to you.
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Lamgda Cold Fusion Model
If you need to troll, please get the basics right. It's called Lambda CDM - CDM for cold dark matter. Check here: https://en.wikipedia.org/wiki/Lambda-CDM_model [wikipedia.org].
"where no one has ever looked before" (Score:3)
We are truly looking for dark matter where no one has ever looked before and that is extremely exciting!
Did they check between the sofa cushions? That's one of the places I always look for stuff I can't find. The stuff always ends up being in the last place I look, though.
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"Dark matter" is about to go the way of phlogiston and luminiferous aether.
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Re:"where no one has ever looked before" (Score:4, Funny)
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There is no dark side of the moon, really. Or the darker side is the one we can see, the one with the huge lava flows. But those socks probably disappeared while still wet, right? This would explain the water ice at the bottom of the permanently shadowed craters. So the place to look is going to be in craters near the poles.
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We are truly looking for dark matter where no one has ever looked before and that is extremely exciting!
Did they check between the sofa cushions? That's one of the places I always look for stuff I can't find. The stuff always ends up being in the last place I look, though.
Dude, the number of times I've found things that fell *through* the couch to the floor when I move the couch years later.... Maybe they should check under the recliner too, while they're at it.
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Thank you for explaining the closing joke of my comment. If anyone did not understand that the bit about checking between sofa cushions was a joke, I hoped the truism would indicate that the earlier suggestion was not intended as a serious approach to finding dark matter. Now I don't have to worry about people understanding that the finale was written with tongue in cheek.
(Full disclosure, in the interest of clarity: It is a lot easier to write things with one's tongue in one's cheek than to say things th
Ain't none (Score:5, Interesting)
Agreed (Score:4, Informative)
Just like newtonian mechanics couldn't explain the orbit of mercury without a load of kludges and then relativity came along and solved it. I suspect we need a whole new branch of physics to find the true answer.
Rename it Epstein Matter, (Score:2)
it only exists when those in charge want it to.
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Have you heard of the bullet cluster's implications for dark matter?
https://en.wikipedia.org/wiki/... [wikipedia.org]
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But I see a flaw in that work. From the article [wikipedia.org]:
However, this study by Clowe et al. made no attempt to analyze the Bullet Cluster using MOND or any other modified gravity theory.
Proof by contradiction would have been much more powerful evidence that dark matter exists. Apply MOND or other theories and show that the results would not fit the measurements. But no. Some people just don't want to test their beliefs [fineartamerica.com].
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"Dark matter is a kludge." No, it isn't. It is a marker for "we need to slot something in here to make our gravity models work." Our gravity models are not wrong in the same sense Newon's theory of gravity was not wrong, merely incomplete or underdetermined would be a better term. But then all scientific models are underdetermined because trying to including every damn thing in the Universe tends to be bit hard.
Another Nail In Supersymmetry's Coffin (Score:1)
Just like the subject says, supersymmetry, an elegant solution to a number of problems, in particular the best theoretical extension to the Standard Model, slides closer to oblivion with each large scale and small scale (accelerator) experiment meant to find these large supersymmetrical particles.
Searching underground? (Score:2)
This is like searching an empty barrel to prove that fish exist in the pond.
-why yes, I like to oversimplify overly complex theories that keep wasting someone else's money that I don't care about.
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A dark matter particle wouldn't interact through the electromagnetic force (that's why it's dark). It would pass right through all that rock almost as if it weren't there.
The same is true of neutrinos, which also don't interact through electromagnetism. Most neutrinos from the sun go right through the earth and continue on their way. They do interact through the weak nuclear force, which is why we can very occasionally detect them. We've ruled out neutrinos as dark matter, but there might be some other
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Yes and no. The idea behind WIMP is, that it very, very rarely interacts with normal matter. So it doesn't really matter where you place the detector and can place it, where you have less background noise. A simple number example, if 99,99% of all WIMPs would pass earth without interaction, it simply doesn't matter, how much rock is above and under the detector, as less than 0,01% of the particles would be eliminated until they could reach the detector. And the true percentage is probably orders of magnitud
A Whole Lot of Aether (Score:1)
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We have lots of evidence that dark matter exists. We just don't know what it is. We have ideas, but we don't know which one is right. To find out, we need to test each of the ideas until we find support for one of them and rule out all the others. This experiment took a step toward (possibly) ruling out one of the ideas.