6 ms·

Biggest dark matter detector spots a single weird particle

346 points by randycupertino 1mo ago

pizzathyme 1mo ago
> it’s far too early to claim a discovery, physicists warn...“How do you even make sense of one event?” muses Tom Shutt, a particle astrophysicist at SLAC National Accelerator Laboratory and co-founder of the LZ project. “We just decided we should publish and think really, really, really hard about what that event could be.” Very hard to manage jumping the gun by reporters. Sounds like they saw some new data. No idea what it is. Looking forward to the follow up.
rajaravivarma_r 1mo ago
I always wondered if it would happen in my lifetime. Hope it turns out to be something interesting (AKA) dark matter.
deleted 1mo ago
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SaberTail 1mo ago
I read their preprint[1] and they did a thorough job. They investigated a number of the things I'd suspect if I were looking for mis-reconstructed events or weird backgrounds. So it's certainly interesting! That said, particle physics history is full of 3 sigma particle "discoveries" that disappeared with more data. They're collecting more, so hopefully we'll learn more in a few more years. [1] https://lz.lbl.gov/wp-content/uploads/sites/6/2026/08/LZ_Preprint_260901_Dark_Matter_EFT_Nuclear_Recoil_Search_at_Higher_Energies.pdf https://lz.lbl.gov/wp-content/uploads/sites/6/2026/08/LZ_Pre...
- smueller1234 1mo ago
  Or this[2] 2007 Science paper on ultra high energy cosmic ray source candidates ("anisotropy") that we had to retract because significance started dropping almost the day the paper was approved. It was a fascinating experience as a junior member to follow the collaboration internal conversation and investigation on this, because a lot of extremely principled scientists were clearly deeply worried about losing their hard earned reputation. In the end, I am convinced that we were simply unlucky. [2] https://arxiv.org/pdf/0712.2843 https://arxiv.org/pdf/0712.2843
  - alexpotato 1mo ago
    > we had to retract because significance started dropping almost the day the paper was approved. It's stories like this that raise my p(we are in a simulation).
  - WarmWash 1mo ago
    Reminds me of the FTL neutrinos too, where the scientist where pretty much "hey, something is wrong, can you help us figure it out?" and the general public were the ones screaming "OMG! Physics is dead!" Then when it comes out as measurement error, the public is all "Damn these scientists are all hype machine clowns..."
    - dd8601fn 1mo ago
      I’m fine with that. Put it at the feet of pop science blogging. I’m less fine with the time and resources spent on mouse models. They already know you’d get the same utility from a magic 8 ball, but they do it anyway.
      - gus_massa 1mo ago
        Mouse models are useful to discard very bad ideas. There was a recent experiment to use bacteria to kill cancer https://news.ycombinator.com/item?id=46306894 https://news.ycombinator.com/item?id=46306894 They tried like 40 bacterias in vitro, then like 9 in mice, and only 1 was useful in mice and they will continue only with that, perhaps in humans. Anyway, as you suggest, there is a high chance it will fail. Also, you can do nasty stuff to mice that would never be allowed with humans. In that experiment they injected cancer cells in mice with a bad inmune system, so they could get like 90 mice with cancer and run the experiment in a short time. No ethical committee would approve that in humans.
      - IAmBroom 1mo ago
        Your claim seems to be that testing medicines in animals is useless, because "everyone knows it's not going to work". Congratulations. You've just reduced all of medical science to the Tuskegee STD experiment.
- derektank 1mo ago
  Are there any other candidate particles besides WIMPs that the observation could be from, assuming it’s a real signal?
  - SaberTail 1mo ago
    In one sense anything that passed all their background rejection is a WIMP. To interact with a nucleus through so much matter, it's not interacting electromagnetically. The main candidate for a strong force interaction would be a neutron, and they did a lot of work to model that and eliminate it as a background. So definitionally it would be a WIMP. They were pretty model agnostic in what they were looking for. They modeled and simulated a number of different ways a WIMP could interact with normal matter. If this is a discovery, more data will be needed to figure out the nature of that interaction and how it fits into particle physics. But there's always a chance it's something completely new, or some extremely rare manifestation of things we already know about, but have never seen before. And even if it is WIMP, it may not be the right type of WIMP (wrong mass, or wrong interaction strength) to explain cosmological dark matter.
    - imglorp 1mo ago
      If neutrons are on the list, how are they ruled out from a random decay event emitting particles, from some mineral in the surrounding rock?
      - physicsdude 1mo ago
        The detector from which data is taken to do this analysis contains 7 tons of liquid xenon. It is inside of a larger detector, which contains hundreds of tons of water and more than 10 tons of a scintillator. One of the functions of that outer detector is to absorb neutrons and other infiltrates coming from the rock. When doing this kind of thing, the analysts will plot the rate of events as a function of "distance from the outer surface" and confirm that it decreases, and in this case "is 0" inside of the detector used for analysis. But keep in mind that all statements are made statistically, so it's not that the event _can't_ be an external neutron, but that it is _very_ unlikely to be.
- matthewdgreen 1mo ago
  This sort of thing is really useful for helping people to understand what the purpose of scientific publication is. It's not about presenting finished products to society, it's more like a Discord where you communicate new findings with other authors. Often the reason for a communication is because you found something weird, and you want other people to know about it so they can help you confirm or rule it out as bad data. People shouldn't feel gunshy about this. (My field even has a conference for failed results, CFAIL.) I like to highlight examples of this stuff, because I see so many angry online comments when a paper turns out to be "wrong" or doesn't replicate.
  - irishcoffee 1mo ago
    You have accurately described a email mailing list. Where in the value-add here?
    - ajkjk 1mo ago
      You think that people's findings should be communicated by email? that their email chains are what should go into the permanent record and be cited and printed out and included in journals and such? would you include all the quoted text in the reply-alls, or is that too much?
      - tomrod 1mo ago
        That's how Linux is built. Science has too many threads to do it successfully though
        Charon77 1mo ago
        > would you include all the quoted text in the reply-alls, or is that too much? Only quote the relevant part and reply to it, just like this very comment. And Linux has a large mailing archive of various lists and threads that are searchable and available to everyone and get this: free access
        1mo ago
- antonvs 1mo ago
  The mainstream TV news report that I saw about this ended with a comment about how we should continue to fund this detector. Made me wonder if the nature of this release involved forces other than purely scientific ones. Apparently funding has already been cut for the successor to the LUX-ZEPLIN detector.
  - physicsdude 1mo ago
    Particle physics is not a particularly large community. There is a hand-countable number of experiments like this, and the folks working on each of them know the folks working on each of the others. The collaborations executing each experiment are comprised of scientists employed by multiple independent institutions, both public and private, typically across national borders. Internally, the collaborations have a democratic structure with individual researchers acting as institutional representatives serving in what is essentially a parliamentary structure to make decisions. The software to determine results is always public within the collaboration and reviewed well in advance of making any truly public disclosure like this. Culturally, an attempt to intentionally distort or misrepresent data to suggest a result like this would not be tolerated. You can imagine a bad actor writing a single-author paper with fakery, but a collaboration at this level is inherently critical of itself and everyone holds each other accountable. But mistakes do happen. Exciting results or hints of exciting results can appear due to well-intentioned researchers making convenient mistakes which get glossed over for psychological reasons and then add up to appear as something significant. You can read about "blinding" (which is mentioned in the paper) to get a feel for the techniques researchers employ to not only guard against fabricating results intentionally, but even unintentionally.
    - IAmBroom 1mo ago
      The small pool also lends itself to a lack of unbiased reviewers. If everyone in the community is more-or-less tied to the research, who can best objectively test it, from a blinded POV?
      - physicsdude 1mo ago
- deleted 1mo ago
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- GuB-42 1mo ago
  > That said, particle physics history is full of 3 sigma particle "discoveries" that disappeared with more data. The idea is that because 3 sigma means a ~1/1000 chance of the thing being explained by random chance, 1 in 1000 experiments will produce a bogus 3 sigma result, and we do many thousands of experiments.
  - adgjlsfhk1 1mo ago
    and also because a result always has the caveats of "if we did our experimental design and math right". A 1/1000 rate of experimental/code design errors will double the number of incorrect 3 sigma results.
lordnacho 1mo ago
So you have 7 tons of Xenon as the detector, hoping that some dark matter will bump into a nucleus. How do you exclude other effects?
- SaberTail 1mo ago
  To start with, they do a lot of work to eliminate radioactive backgrounds in the materials they're using, and they put the detector deep underground to shield from cosmic rays. Additionally, when a particle interacts with the nucleus, the ratio of how much energy ends up as scintillation light versus ionization is different than when a particle interacts with an electron, which is most of the background processes. Then, whatever is left, they try to model using known processes. After all that, there's one event that they can't account for. And that's what the news is about.
  - gus_massa 1mo ago
    I agree. Moreover, I'm not sure if it's the same team, but in a similar experiment while removing all the other effects, they discovered that Xenon 124 is radioactive, but the half life is super long and no one had seen it before. https://xenonexperiment.org/observing-the-rarest-decay-process-ever-measured/ https://xenonexperiment.org/observing-the-rarest-decay-proce...
    - vintermann 1mo ago
      That's a pretty cool discovery in its own right.
      - jakzurr 1mo ago
        Wow! That's in https://en.wikipedia.org/wiki/Xenon https://en.wikipedia.org/wiki/Xenon now. Xe-124, half-life 1.1 * 10^22 years. That's crazy.
    - cogman10 1mo ago
      Makes me wonder if all atoms with 2+ nucleus elements (protons and neutrons) are radioactive but the halflife is so far out as to make something we'll never detect.
amemi 1mo ago
Not well informed on the topic- but the title made me think of the recently launched Roman Space Telescope. The difference: LUX-ZEPLIN, which is underground, is waiting to detect a dark matter particle itself. On the other hand, NGRST seeks to observe the effects of dark matter.
deleted 1mo ago
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parineum 1mo ago
> If the new result is real, more signals should emerge soon. LZ researchers have already collected three times as much data as they used in the paper. It sounds like this implies they've seen 3x more events but it seems like they would have said that if it were the case. Have they just gathered more data about the single event or is this 4 separate events they're talking about?
- IsTom 1mo ago
  If this anything like CERN detectors, they get amounts of data so vast that they have to discard almost all of it to be even able to record it. Depending on heurestics you use to discard data you might be discarding what you are looking for and after adjustment will get some new interesting events, but still actually processing the candidates might take a long time.
  - physicsdude 1mo ago
    This raises what is (I think) an interesting question. CERN is a collider, so they are _trying_ to produce lots of stuff, and they do (lots and lots of stuff). They can't write it all to disk, and most of it isn't interesting enough to try. The work being done here falls into the category of "low background physics" --- they aren't trying to produce anything, and actually put quite a bit of effort into doing the opposite, by removing all sources of particles (e.g. sourcing materials free of radioactive contaminants, physically cleaning all surfaces and purifying all fluids involved, etc). So the detector, if built properly, is fairly quiet, and you try to write as much data to disk as you can (e.g., if something even fairly-potentially interesting happens, you save it). Then when you analyze the data like this, you ignore the majority of what you've got --- only a teeny fraction makes it into an analysis of this caliber.
    - thiagotomei 1mo ago
      I think this description is essentially correct.
- SaberTail 1mo ago
scotty79 1mo ago
Why couldn't it be just a weirdly energetic neutrino originating from the neighborhood of some black hole?
- physicsdude 1mo ago
  At some level, it could be (and that would be an great discovery as well!). It's a question of probabilities: it's unlikely to be any of the things that we already know about, but that doesn't mean that it's something new. Unlikely things happen --- infrequently. As stressed in the article and elsewhere in comments, more data should elucidate what is going on. That's the difficulty of these kinds of searches: there is one event, and we can't make clear, confident statements about one event.
- procflora 1mo ago
  Based on my very amateurish skim of this and a related paper, maybe so? They simulated the neutrino background as solar and cosmic ray atmospheric sources, so any source with a different energy distribution is perhaps a possible explanation for the event, I think. But probably more likely is for this to have been a particularly energetic event in the tail of one of the known sources of neutron recoil detection they did model. More events needed!
- hershkumar 1mo ago
  I actually saw one of the authors present the data yesterday, one of the audience comments was indeed that this could be explained by an astrophysical neutrino striking the detector (all other neutrino sources have energy thresholds much lower than the detected data), but the data on astrophysical neutrinos is sparse (in part why detectors like IceCube exist), so I believe the argument is that the chances that an astrophysical neutrino would strike the detector is negligible.
  - scotty79 1mo ago
    Thank you very much for this first hand info. One might argue that chances of theoretical particle existing and showing up are at least as negligible.
petcat 1mo ago
> The detector lurks 1480 meters deep in the Sanford Underground Research Facility, in a former gold mine in South Dakota. Glad to see such things getting re-purposed instead of just sealed off and abandoned.
gwbas1c 1mo ago
I think it's cool that there's still unconfirmed hypothesizes, and still unexplained phenomena in the science that's investigating these hypothesizes. I hope this turns into a real discovery about something; but even if it's an equipment malfunction, hopefully it's a lesson that can be turned into improving the detector.
- BurningFrog 1mo ago
  Astronomy/Physics is overflowing with unexplained physics phenomena these days. Especially after JWT started looking deeper into the early universe.
- strogonoff 1mo ago
  The moment there are no more unconfirmed hypotheses you can assume something is wrong with sciences. All provable models (theories, explanations) that we have, or could have, are by definition wrong or incomplete.
  - tsimionescu 1mo ago
    I'm guessing you're alluding to Goedel's incompleteness theorem, but that really doesn't apply to physics. It's a statement about certain properties of formal systems - basically it tells us that for any formal system that's at least as powerful as arithmetic, it's impossible to prove every statement that is true in that system. This doesn't in any way mean that you can't in principle describe with perfect accuracy with such a system, in a provable way, every aspect of physics. Sure, you might need a theorem that can't be proved and be stuck because of that, but it's not a given. Physics certainly doesn't depend on all possible statements in that formal system to accurately model the real world, and so Goedel's theorem can't prove that the subset that physics needs might not be all probable.
    - birdland 1mo ago
      I don't think Gödel is necessarily what is meant here, there are very good information theoretical(and other) reasons you can never describe a system with truly perfect accuracy. The map has to be become the territory for genuinely perfect accuracy.
advisedwang 1mo ago
> Such behavior could require dark matter to be more complicated than just a single new type of particle. For example, the dark matter particle might have some internal structure, like an ordinary atom, so it would only interact if hit hard enough to excite it to a higher energy internal state I get a little shiver imagining that the dark matter might be something like ordinary atoms. Imagine that other 85% of the universe could have its own parallel atomic table, chemistry, even some kind of life utterly alien to us?
- hyperhello 1mo ago
  It's possible that there could be an entirely different charge mechanism that works exactly like ours but they don't interact at all; but the whole premise of dark matter is that it doesn't seem to have any self-interaction outside of gravity.
  - gizmo686 1mo ago
    The premise of dark matter is that it is something with gravity that does not otherwise interact with any of our detectors (e.g. "normal" matter); or that any such interactions are weak enough that it is plausible we have not noticed. By itself, that does not exclude the possibility of dark matter having other interactions which do not interfere with our detectors.
    - hyperhello 1mo ago
      I guess so. If you could sort of measure the dark matter distribution, there might be a structure under it, but strictly speaking isn’t it limited to saying it’s not at least likely to emit light but does have mass.
    - XorNot 1mo ago
      But it does bound it: if dark matter has self-interactions then the apparent distribution would be different. Regular matter forms stars and galaxies and all the structures we see because it can self-interact. Since where we see dark matter mass shadows we don't see structure formation, what self interaction it may have must be very, very limited.
DrJokepu 1mo ago
This is 1σ. It’s fun and interesting, but means nothing.
- marcosdumay 1mo ago
  > LZ physicists estimate there’s about a one in 200 chance the event is a statistical fluke That's more than 3σ.
wewewedxfgdf 1mo ago
Such detectors will never see dark matter because it is little black holes.
- throwawayffffas 1mo ago
  Depending on the size of the black holes these detectors can see them.
I_am_tiberius 1mo ago
i have zero knowledge of physics, but I just can't believe something like dark matter exists. My intuition is that some math just isn't correct and falls apart at the scales of the observable universe. No idea what equations are used for getting to the reslut of having 85% unexplained matter in the universe, but I really assume there's just a constant missing or our math in general just inaccurate or not considering specific effects.
- root_axis 1mo ago
  I'm not a physicist either, but the amount of evidence pointing in the direction of dark matter is extremely significant, it's a little silly to just dismiss all that based on your intuition.
- defrost 1mo ago
  > No idea what equations are used for getting to the result "Basic" gravitational equations applied to observed behaviour: clumping and rotation of galaxies, lensing (light bending), etc. The behaviour implies "something" is exerting force in a mass like way - but there's a shortfall of visible mass. The observational hole left by the apparent behaviour of "unseen matter" attracts a lot of theory. * Physics "allows for" various types of particles with various types of properties - these may or may not all exist, some do. eg: Neutrino's from the sun barely interact with anything, consistently capturing them is a challenge. Maybe Dark Matter is a new hard to observe gravity particle. * Physics has equations formed by "human scale" observation and sometimes tweaked for scales beyond direct human experience. eg: relativistic tweaks related to speeds approaching that of light. Maybe Dark Matter is a warping of observation at galaxy scale. The opening paragraphs of, say, https://en.wikipedia.org/wiki/Dark_matter https://en.wikipedia.org/wiki/Dark_matter cover the ground of speculation.
- magicalhippo 1mo ago
  For those who are interested in learning why physicists think dark matter exists, there's an excellent and accessible talk[1] freely available over at PIRSA where an astrophysicist goes through exactly what we know about the universe and how many different kinds of evidence all seem to point in a similar direction: dark matter exists. [1]: https://pirsa.org/26030070 https://pirsa.org/26030070
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hirshi 1mo ago
How many years until we've discovered "everything"?
- jesse_dot_id 1mo ago
  Probably never. We've only mapped like 29% of the seafloor, actually explored like %5 of it, and we've barely pierced the earth's crust.
  - kypro 1mo ago
    I never understood why people cite this as a demonstration for how little we humans understand about our world. The reason we haven't mapped the seafloor is because why would we? It's like arguing we know nothing about biology because we've only sequenced the genome of a fraction of humans or something. It's not that we can't do it, the reason we haven't done it is because there's no good compelling reason to do it. What do we expect to learn from mapping 100% of the sea floor? As for the parents question – "How many years until we've discovered "everything"?" I think we may be fairly close to knowing everything we can know and it's quite reasonable to assume we're now comfortably on the tail end of the S-curve of physics discoveries. I hope I'm wrong of course.
    - ourmandave 1mo ago
      I'm a complete layman but it seems like we've got a long way to go and history will look back on us like we do on Newtonian Physics. Just given dark matter and energy, things the standard model doesn't answer, and our evolving tools (e.g. Grace telescope, etc.).
      - kypro 1mo ago
        To expand a little, my prediction is based on the fact that we can already explain the vast majority of physical processes with extreme procession. The things we can't explain tend to be very small, very large or very quick. But there's almost nothing in our day to day lives that we can't explain anymore. This means that today to make new discoveries we tend to have to invest huge sums of money and build experiments that we'll increasingly struggle to scale significantly beyond. For example, maybe humans could just about build something 10x the size of the LHC if we really wanted, but 100x seems near-impossible. Maybe we can build slightly larger telescopes, but again, this is becoming harder due to the scale we're already working at. So while I agree there's probably lots of physics out there to discover, the physics we humans are actually likely to be able to discover is rapidly diminishing. And the physics which is likely to revolutionise our daily lives is presumably even smaller more due to scale and energy levels where mysteries remain. But ultimately who knows, this is just my opinion – an opinion I'm being downvoted for because apparently HN discussions these days are a place for us circlejerk around the consensus view rather than discuss differences in opinion.
sandworm101 1mo ago
>> or the far bigger next version of the PandaX detector, currently under development in China... Has there ever been an article about particle physics that didnt end with a statement about the "next and bigger" version of the current detector. The field has an addiction. No matter the size/luminocity, they will only ever crave a bigger hit. One wonders if we should measure detectors as we do nuclear bombs: by the kiloton mass of thier detection medium. The DUNE detector would be a 70 kiloton-class detector. Super-Kamiokande, 50kt. IceCube would be approaching a gigaton.
jrgirvan 1mo ago
So much money wasted on dark*
sylware 1mo ago
This is statistical significance ! WE NEED A BIGGER DETECTOR! GI'ME MONEY!
- evanb 1mo ago
  The total cost of this experiment may be a lot less than you expect. I'd encourage you to make a guess as to what you think it could cost the US taxpayer and then check what the Department of Energy contributed [1]. The LZ collaboration is going to run their machine until at least 2030. They have almost no hope of making a meaningfully larger detector, no will you hear them suggest one. Their detector is already designed at such a scale that it contains a substantial fraction of all the needed xenon isotope available on Earth. [1] https://news.wisc.edu/dark-matter-detection-receives-10-ton-upgrade/ https://news.wisc.edu/dark-matter-detection-receives-10-ton-...
  - sylware 29d ago
    So this is a big enough detector? That would mean they need to wait for such events to occur again and again towards this "5sigmas". Hopefully, other aparatus elsewhere are big enough too in order to spot similar events.
    - evanb 28d ago
      No one knows if it’s big enough—-that depends on the properties of dark matter and its interaction with xenon.
      - sylware 27d ago
        It is all about that single data point, which means that detector was big enough for that data point.
        evanb 26d ago
        But you could collect this data point by chance in a bigger or smaller detector. What I was addressing was whether this detector is big enough for a reliable discovery. In that case what you really want to constrain is the rate, such-and-such events per kilogram of xenon per year (the per-kilogram-of-xenon can be traded for a per-liter rate given the density of the xenon).
leumassuehtam 1mo ago
[dead]
Unified-Mentor 1mo ago
[dead]
naasking 1mo ago
They detected a single weird event, not necessarily a particle.
bronlund 1mo ago
Another particle! Who would have guessed %]
butlike 1mo ago
I'm out of touch and 5 years old, so please someone explain to me, but I thought the galaxies were bound together by divets in spacetime based on their mass dictated by the Higgs field. Now its dark matter binding the galaxies together?

346 points by randycupertino 1mo ago

> it’s far too early to claim a discovery, physicists warn...“How do you even make sense of one event?” muses Tom Shutt, a particle astrophysicist at SLAC National Accelerator Laboratory and co-founder of the LZ project. “We just decided we should publish and think really, really, really hard about what that event could be.” Very hard to manage jumping the gun by reporters. Sounds like they saw some new data. No idea what it is. Looking forward to the follow up.

rajaravivarma_r 1mo ago

I always wondered if it would happen in my lifetime. Hope it turns out to be something interesting (AKA) dark matter.

deleted 1mo ago

[deleted]

SaberTail 1mo ago

I read their preprint[1] and they did a thorough job. They investigated a number of the things I'd suspect if I were looking for mis-reconstructed events or weird backgrounds. So it's certainly interesting! That said, particle physics history is full of 3 sigma particle "discoveries" that disappeared with more data. They're collecting more, so hopefully we'll learn more in a few more years. [1] https://lz.lbl.gov/wp-content/uploads/sites/6/2026/08/LZ_Preprint_260901_Dark_Matter_EFT_Nuclear_Recoil_Search_at_Higher_Energies.pdf https://lz.lbl.gov/wp-content/uploads/sites/6/2026/08/LZ_Pre...

smueller1234 1mo ago
Or this[2] 2007 Science paper on ultra high energy cosmic ray source candidates ("anisotropy") that we had to retract because significance started dropping almost the day the paper was approved. It was a fascinating experience as a junior member to follow the collaboration internal conversation and investigation on this, because a lot of extremely principled scientists were clearly deeply worried about losing their hard earned reputation. In the end, I am convinced that we were simply unlucky. [2] https://arxiv.org/pdf/0712.2843 https://arxiv.org/pdf/0712.2843
- alexpotato 1mo ago
  > we had to retract because significance started dropping almost the day the paper was approved. It's stories like this that raise my p(we are in a simulation).
- WarmWash 1mo ago
  Reminds me of the FTL neutrinos too, where the scientist where pretty much "hey, something is wrong, can you help us figure it out?" and the general public were the ones screaming "OMG! Physics is dead!" Then when it comes out as measurement error, the public is all "Damn these scientists are all hype machine clowns..."
  - dd8601fn 1mo ago
    I’m fine with that. Put it at the feet of pop science blogging. I’m less fine with the time and resources spent on mouse models. They already know you’d get the same utility from a magic 8 ball, but they do it anyway.
    - gus_massa 1mo ago
      Mouse models are useful to discard very bad ideas. There was a recent experiment to use bacteria to kill cancer https://news.ycombinator.com/item?id=46306894 https://news.ycombinator.com/item?id=46306894 They tried like 40 bacterias in vitro, then like 9 in mice, and only 1 was useful in mice and they will continue only with that, perhaps in humans. Anyway, as you suggest, there is a high chance it will fail. Also, you can do nasty stuff to mice that would never be allowed with humans. In that experiment they injected cancer cells in mice with a bad inmune system, so they could get like 90 mice with cancer and run the experiment in a short time. No ethical committee would approve that in humans.
    - IAmBroom 1mo ago
      Your claim seems to be that testing medicines in animals is useless, because "everyone knows it's not going to work". Congratulations. You've just reduced all of medical science to the Tuskegee STD experiment.
derektank 1mo ago
Are there any other candidate particles besides WIMPs that the observation could be from, assuming it’s a real signal?
- SaberTail 1mo ago
  In one sense anything that passed all their background rejection is a WIMP. To interact with a nucleus through so much matter, it's not interacting electromagnetically. The main candidate for a strong force interaction would be a neutron, and they did a lot of work to model that and eliminate it as a background. So definitionally it would be a WIMP. They were pretty model agnostic in what they were looking for. They modeled and simulated a number of different ways a WIMP could interact with normal matter. If this is a discovery, more data will be needed to figure out the nature of that interaction and how it fits into particle physics. But there's always a chance it's something completely new, or some extremely rare manifestation of things we already know about, but have never seen before. And even if it is WIMP, it may not be the right type of WIMP (wrong mass, or wrong interaction strength) to explain cosmological dark matter.
  - imglorp 1mo ago
    If neutrons are on the list, how are they ruled out from a random decay event emitting particles, from some mineral in the surrounding rock?
    - physicsdude 1mo ago
      The detector from which data is taken to do this analysis contains 7 tons of liquid xenon. It is inside of a larger detector, which contains hundreds of tons of water and more than 10 tons of a scintillator. One of the functions of that outer detector is to absorb neutrons and other infiltrates coming from the rock. When doing this kind of thing, the analysts will plot the rate of events as a function of "distance from the outer surface" and confirm that it decreases, and in this case "is 0" inside of the detector used for analysis. But keep in mind that all statements are made statistically, so it's not that the event _can't_ be an external neutron, but that it is _very_ unlikely to be.
matthewdgreen 1mo ago
This sort of thing is really useful for helping people to understand what the purpose of scientific publication is. It's not about presenting finished products to society, it's more like a Discord where you communicate new findings with other authors. Often the reason for a communication is because you found something weird, and you want other people to know about it so they can help you confirm or rule it out as bad data. People shouldn't feel gunshy about this. (My field even has a conference for failed results, CFAIL.) I like to highlight examples of this stuff, because I see so many angry online comments when a paper turns out to be "wrong" or doesn't replicate.
- irishcoffee 1mo ago
  You have accurately described a email mailing list. Where in the value-add here?
  - ajkjk 1mo ago
    You think that people's findings should be communicated by email? that their email chains are what should go into the permanent record and be cited and printed out and included in journals and such? would you include all the quoted text in the reply-alls, or is that too much?
    - tomrod 1mo ago
      That's how Linux is built. Science has too many threads to do it successfully though
      - Charon77 1mo ago
        > would you include all the quoted text in the reply-alls, or is that too much? Only quote the relevant part and reply to it, just like this very comment. And Linux has a large mailing archive of various lists and threads that are searchable and available to everyone and get this: free access
        1mo ago
antonvs 1mo ago
The mainstream TV news report that I saw about this ended with a comment about how we should continue to fund this detector. Made me wonder if the nature of this release involved forces other than purely scientific ones. Apparently funding has already been cut for the successor to the LUX-ZEPLIN detector.
- physicsdude 1mo ago
  Particle physics is not a particularly large community. There is a hand-countable number of experiments like this, and the folks working on each of them know the folks working on each of the others. The collaborations executing each experiment are comprised of scientists employed by multiple independent institutions, both public and private, typically across national borders. Internally, the collaborations have a democratic structure with individual researchers acting as institutional representatives serving in what is essentially a parliamentary structure to make decisions. The software to determine results is always public within the collaboration and reviewed well in advance of making any truly public disclosure like this. Culturally, an attempt to intentionally distort or misrepresent data to suggest a result like this would not be tolerated. You can imagine a bad actor writing a single-author paper with fakery, but a collaboration at this level is inherently critical of itself and everyone holds each other accountable. But mistakes do happen. Exciting results or hints of exciting results can appear due to well-intentioned researchers making convenient mistakes which get glossed over for psychological reasons and then add up to appear as something significant. You can read about "blinding" (which is mentioned in the paper) to get a feel for the techniques researchers employ to not only guard against fabricating results intentionally, but even unintentionally.
  - IAmBroom 1mo ago
    The small pool also lends itself to a lack of unbiased reviewers. If everyone in the community is more-or-less tied to the research, who can best objectively test it, from a blinded POV?
    - physicsdude 1mo ago
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GuB-42 1mo ago
> That said, particle physics history is full of 3 sigma particle "discoveries" that disappeared with more data. The idea is that because 3 sigma means a ~1/1000 chance of the thing being explained by random chance, 1 in 1000 experiments will produce a bogus 3 sigma result, and we do many thousands of experiments.
- adgjlsfhk1 1mo ago
  and also because a result always has the caveats of "if we did our experimental design and math right". A 1/1000 rate of experimental/code design errors will double the number of incorrect 3 sigma results.

lordnacho 1mo ago

So you have 7 tons of Xenon as the detector, hoping that some dark matter will bump into a nucleus. How do you exclude other effects?

SaberTail 1mo ago
To start with, they do a lot of work to eliminate radioactive backgrounds in the materials they're using, and they put the detector deep underground to shield from cosmic rays. Additionally, when a particle interacts with the nucleus, the ratio of how much energy ends up as scintillation light versus ionization is different than when a particle interacts with an electron, which is most of the background processes. Then, whatever is left, they try to model using known processes. After all that, there's one event that they can't account for. And that's what the news is about.
- gus_massa 1mo ago
  I agree. Moreover, I'm not sure if it's the same team, but in a similar experiment while removing all the other effects, they discovered that Xenon 124 is radioactive, but the half life is super long and no one had seen it before. https://xenonexperiment.org/observing-the-rarest-decay-process-ever-measured/ https://xenonexperiment.org/observing-the-rarest-decay-proce...
  - vintermann 1mo ago
    That's a pretty cool discovery in its own right.
    - jakzurr 1mo ago
      Wow! That's in https://en.wikipedia.org/wiki/Xenon https://en.wikipedia.org/wiki/Xenon now. Xe-124, half-life 1.1 * 10^22 years. That's crazy.
  - cogman10 1mo ago
    Makes me wonder if all atoms with 2+ nucleus elements (protons and neutrons) are radioactive but the halflife is so far out as to make something we'll never detect.

amemi 1mo ago

Not well informed on the topic- but the title made me think of the recently launched Roman Space Telescope. The difference: LUX-ZEPLIN, which is underground, is waiting to detect a dark matter particle itself. On the other hand, NGRST seeks to observe the effects of dark matter.

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parineum 1mo ago

> If the new result is real, more signals should emerge soon. LZ researchers have already collected three times as much data as they used in the paper. It sounds like this implies they've seen 3x more events but it seems like they would have said that if it were the case. Have they just gathered more data about the single event or is this 4 separate events they're talking about?

IsTom 1mo ago
If this anything like CERN detectors, they get amounts of data so vast that they have to discard almost all of it to be even able to record it. Depending on heurestics you use to discard data you might be discarding what you are looking for and after adjustment will get some new interesting events, but still actually processing the candidates might take a long time.
- physicsdude 1mo ago
  This raises what is (I think) an interesting question. CERN is a collider, so they are _trying_ to produce lots of stuff, and they do (lots and lots of stuff). They can't write it all to disk, and most of it isn't interesting enough to try. The work being done here falls into the category of "low background physics" --- they aren't trying to produce anything, and actually put quite a bit of effort into doing the opposite, by removing all sources of particles (e.g. sourcing materials free of radioactive contaminants, physically cleaning all surfaces and purifying all fluids involved, etc). So the detector, if built properly, is fairly quiet, and you try to write as much data to disk as you can (e.g., if something even fairly-potentially interesting happens, you save it). Then when you analyze the data like this, you ignore the majority of what you've got --- only a teeny fraction makes it into an analysis of this caliber.
  - thiagotomei 1mo ago
    I think this description is essentially correct.
SaberTail 1mo ago

scotty79 1mo ago

Why couldn't it be just a weirdly energetic neutrino originating from the neighborhood of some black hole?

physicsdude 1mo ago
At some level, it could be (and that would be an great discovery as well!). It's a question of probabilities: it's unlikely to be any of the things that we already know about, but that doesn't mean that it's something new. Unlikely things happen --- infrequently. As stressed in the article and elsewhere in comments, more data should elucidate what is going on. That's the difficulty of these kinds of searches: there is one event, and we can't make clear, confident statements about one event.
procflora 1mo ago
Based on my very amateurish skim of this and a related paper, maybe so? They simulated the neutrino background as solar and cosmic ray atmospheric sources, so any source with a different energy distribution is perhaps a possible explanation for the event, I think. But probably more likely is for this to have been a particularly energetic event in the tail of one of the known sources of neutron recoil detection they did model. More events needed!
hershkumar 1mo ago
I actually saw one of the authors present the data yesterday, one of the audience comments was indeed that this could be explained by an astrophysical neutrino striking the detector (all other neutrino sources have energy thresholds much lower than the detected data), but the data on astrophysical neutrinos is sparse (in part why detectors like IceCube exist), so I believe the argument is that the chances that an astrophysical neutrino would strike the detector is negligible.
- scotty79 1mo ago
  Thank you very much for this first hand info. One might argue that chances of theoretical particle existing and showing up are at least as negligible.

petcat 1mo ago

> The detector lurks 1480 meters deep in the Sanford Underground Research Facility, in a former gold mine in South Dakota. Glad to see such things getting re-purposed instead of just sealed off and abandoned.

gwbas1c 1mo ago

I think it's cool that there's still unconfirmed hypothesizes, and still unexplained phenomena in the science that's investigating these hypothesizes. I hope this turns into a real discovery about something; but even if it's an equipment malfunction, hopefully it's a lesson that can be turned into improving the detector.

BurningFrog 1mo ago
Astronomy/Physics is overflowing with unexplained physics phenomena these days. Especially after JWT started looking deeper into the early universe.
strogonoff 1mo ago
The moment there are no more unconfirmed hypotheses you can assume something is wrong with sciences. All provable models (theories, explanations) that we have, or could have, are by definition wrong or incomplete.
- tsimionescu 1mo ago
  I'm guessing you're alluding to Goedel's incompleteness theorem, but that really doesn't apply to physics. It's a statement about certain properties of formal systems - basically it tells us that for any formal system that's at least as powerful as arithmetic, it's impossible to prove every statement that is true in that system. This doesn't in any way mean that you can't in principle describe with perfect accuracy with such a system, in a provable way, every aspect of physics. Sure, you might need a theorem that can't be proved and be stuck because of that, but it's not a given. Physics certainly doesn't depend on all possible statements in that formal system to accurately model the real world, and so Goedel's theorem can't prove that the subset that physics needs might not be all probable.
  - birdland 1mo ago
    I don't think Gödel is necessarily what is meant here, there are very good information theoretical(and other) reasons you can never describe a system with truly perfect accuracy. The map has to be become the territory for genuinely perfect accuracy.

advisedwang 1mo ago

> Such behavior could require dark matter to be more complicated than just a single new type of particle. For example, the dark matter particle might have some internal structure, like an ordinary atom, so it would only interact if hit hard enough to excite it to a higher energy internal state I get a little shiver imagining that the dark matter might be something like ordinary atoms. Imagine that other 85% of the universe could have its own parallel atomic table, chemistry, even some kind of life utterly alien to us?

hyperhello 1mo ago
It's possible that there could be an entirely different charge mechanism that works exactly like ours but they don't interact at all; but the whole premise of dark matter is that it doesn't seem to have any self-interaction outside of gravity.
- gizmo686 1mo ago
  The premise of dark matter is that it is something with gravity that does not otherwise interact with any of our detectors (e.g. "normal" matter); or that any such interactions are weak enough that it is plausible we have not noticed. By itself, that does not exclude the possibility of dark matter having other interactions which do not interfere with our detectors.
  - hyperhello 1mo ago
    I guess so. If you could sort of measure the dark matter distribution, there might be a structure under it, but strictly speaking isn’t it limited to saying it’s not at least likely to emit light but does have mass.
  - XorNot 1mo ago
    But it does bound it: if dark matter has self-interactions then the apparent distribution would be different. Regular matter forms stars and galaxies and all the structures we see because it can self-interact. Since where we see dark matter mass shadows we don't see structure formation, what self interaction it may have must be very, very limited.

DrJokepu 1mo ago

This is 1σ. It’s fun and interesting, but means nothing.

marcosdumay 1mo ago
> LZ physicists estimate there’s about a one in 200 chance the event is a statistical fluke That's more than 3σ.

wewewedxfgdf 1mo ago

Such detectors will never see dark matter because it is little black holes.

throwawayffffas 1mo ago
Depending on the size of the black holes these detectors can see them.

I_am_tiberius 1mo ago

i have zero knowledge of physics, but I just can't believe something like dark matter exists. My intuition is that some math just isn't correct and falls apart at the scales of the observable universe. No idea what equations are used for getting to the reslut of having 85% unexplained matter in the universe, but I really assume there's just a constant missing or our math in general just inaccurate or not considering specific effects.

root_axis 1mo ago
I'm not a physicist either, but the amount of evidence pointing in the direction of dark matter is extremely significant, it's a little silly to just dismiss all that based on your intuition.
defrost 1mo ago
> No idea what equations are used for getting to the result "Basic" gravitational equations applied to observed behaviour: clumping and rotation of galaxies, lensing (light bending), etc. The behaviour implies "something" is exerting force in a mass like way - but there's a shortfall of visible mass. The observational hole left by the apparent behaviour of "unseen matter" attracts a lot of theory. * Physics "allows for" various types of particles with various types of properties - these may or may not all exist, some do. eg: Neutrino's from the sun barely interact with anything, consistently capturing them is a challenge. Maybe Dark Matter is a new hard to observe gravity particle. * Physics has equations formed by "human scale" observation and sometimes tweaked for scales beyond direct human experience. eg: relativistic tweaks related to speeds approaching that of light. Maybe Dark Matter is a warping of observation at galaxy scale. The opening paragraphs of, say, https://en.wikipedia.org/wiki/Dark_matter https://en.wikipedia.org/wiki/Dark_matter cover the ground of speculation.
magicalhippo 1mo ago
For those who are interested in learning why physicists think dark matter exists, there's an excellent and accessible talk[1] freely available over at PIRSA where an astrophysicist goes through exactly what we know about the universe and how many different kinds of evidence all seem to point in a similar direction: dark matter exists. [1]: https://pirsa.org/26030070 https://pirsa.org/26030070

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hirshi 1mo ago

How many years until we've discovered "everything"?

jesse_dot_id 1mo ago
Probably never. We've only mapped like 29% of the seafloor, actually explored like %5 of it, and we've barely pierced the earth's crust.
- kypro 1mo ago
  I never understood why people cite this as a demonstration for how little we humans understand about our world. The reason we haven't mapped the seafloor is because why would we? It's like arguing we know nothing about biology because we've only sequenced the genome of a fraction of humans or something. It's not that we can't do it, the reason we haven't done it is because there's no good compelling reason to do it. What do we expect to learn from mapping 100% of the sea floor? As for the parents question – "How many years until we've discovered "everything"?" I think we may be fairly close to knowing everything we can know and it's quite reasonable to assume we're now comfortably on the tail end of the S-curve of physics discoveries. I hope I'm wrong of course.
  - ourmandave 1mo ago
    I'm a complete layman but it seems like we've got a long way to go and history will look back on us like we do on Newtonian Physics. Just given dark matter and energy, things the standard model doesn't answer, and our evolving tools (e.g. Grace telescope, etc.).
    - kypro 1mo ago
      To expand a little, my prediction is based on the fact that we can already explain the vast majority of physical processes with extreme procession. The things we can't explain tend to be very small, very large or very quick. But there's almost nothing in our day to day lives that we can't explain anymore. This means that today to make new discoveries we tend to have to invest huge sums of money and build experiments that we'll increasingly struggle to scale significantly beyond. For example, maybe humans could just about build something 10x the size of the LHC if we really wanted, but 100x seems near-impossible. Maybe we can build slightly larger telescopes, but again, this is becoming harder due to the scale we're already working at. So while I agree there's probably lots of physics out there to discover, the physics we humans are actually likely to be able to discover is rapidly diminishing. And the physics which is likely to revolutionise our daily lives is presumably even smaller more due to scale and energy levels where mysteries remain. But ultimately who knows, this is just my opinion – an opinion I'm being downvoted for because apparently HN discussions these days are a place for us circlejerk around the consensus view rather than discuss differences in opinion.

sandworm101 1mo ago

>> or the far bigger next version of the PandaX detector, currently under development in China... Has there ever been an article about particle physics that didnt end with a statement about the "next and bigger" version of the current detector. The field has an addiction. No matter the size/luminocity, they will only ever crave a bigger hit. One wonders if we should measure detectors as we do nuclear bombs: by the kiloton mass of thier detection medium. The DUNE detector would be a 70 kiloton-class detector. Super-Kamiokande, 50kt. IceCube would be approaching a gigaton.

jrgirvan 1mo ago

So much money wasted on dark*

sylware 1mo ago

This is statistical significance ! WE NEED A BIGGER DETECTOR! GI'ME MONEY!

evanb 1mo ago
The total cost of this experiment may be a lot less than you expect. I'd encourage you to make a guess as to what you think it could cost the US taxpayer and then check what the Department of Energy contributed [1]. The LZ collaboration is going to run their machine until at least 2030. They have almost no hope of making a meaningfully larger detector, no will you hear them suggest one. Their detector is already designed at such a scale that it contains a substantial fraction of all the needed xenon isotope available on Earth. [1] https://news.wisc.edu/dark-matter-detection-receives-10-ton-upgrade/ https://news.wisc.edu/dark-matter-detection-receives-10-ton-...
- sylware 29d ago
  So this is a big enough detector? That would mean they need to wait for such events to occur again and again towards this "5sigmas". Hopefully, other aparatus elsewhere are big enough too in order to spot similar events.
  - evanb 28d ago
    No one knows if it’s big enough—-that depends on the properties of dark matter and its interaction with xenon.
    - sylware 27d ago
      It is all about that single data point, which means that detector was big enough for that data point.
      - evanb 26d ago
        But you could collect this data point by chance in a bigger or smaller detector. What I was addressing was whether this detector is big enough for a reliable discovery. In that case what you really want to constrain is the rate, such-and-such events per kilogram of xenon per year (the per-kilogram-of-xenon can be traded for a per-liter rate given the density of the xenon).

leumassuehtam 1mo ago

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Unified-Mentor 1mo ago

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naasking 1mo ago

They detected a single weird event, not necessarily a particle.

bronlund 1mo ago

Another particle! Who would have guessed %]

butlike 1mo ago

I'm out of touch and 5 years old, so please someone explain to me, but I thought the galaxies were bound together by divets in spacetime based on their mass dictated by the Higgs field. Now its dark matter binding the galaxies together?