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SaberTail 1 days 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.
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.
stouset 1 days ago [-]
Yep. Publishing like this gives a heads up to those operating similar observatories to keep an eye out for similar events. And it gives a nudge to theorists that might help them start looking in a more fruitful direction, appropriately caveated that it may be a statistical fluke.
megagpt2 1 days ago [-]
They were - in the past. I imagine that right now, Discord is their Discord.
irishcoffee 1 days ago [-]
You have accurately described a email mailing list. Where in the value-add here?
EthanHeilman 1 days ago [-]
> You have accurately described a email mailing list. Where in the value-add here?
Pre-prints are basically a mailinglist where you post your paper prior to peer review.
The value over a simple mailinglist is:
1. Stable URL and citation to enable other work and discussions to cite and reference it.
2. Versioning of the paper, allowing updates to be made without having mail out the paper, while allowing everyone to find all prior versions
3. Host for a PDF and data that might be quite large
4. Centralized searchable long term archive of scientific papers
5. Scalability, arxiv gets 30,000 submissions a day, no one wants to receive 30,000 PDFs in their inbox everyday
gus_massa 1 days ago [-]
No so wrong. The oldest journals started as smailing list :)
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?
tokai 17 hours ago [-]
Have you never seen a 'personal correspondence' reference?
ajkjk 7 hours ago [-]
the fact that they are sometimes communicated by email doesn't mean that the best way to communicate them is by email. Personal correspondence references are specifically terrible as references since you can't go read them...
evanb 15 hours ago [-]
Yeah but no matter how hard I look I never seem to be able to read anyone else's email. Maybe OpenAI's upcoming models can help me find those references.
tomrod 1 days ago [-]
That's how Linux is built.
Science has too many threads to do it successfully though
Charon77 1 days 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
ajkjk 1 days ago [-]
The linux developers' mailing lists are not producing anything like scientific papers...
bdamm 1 days ago [-]
Kind of arrogant no? Linux kernel development mailing lists are producing something immensely valuable with a much clearer impact on economic indicators than your average scientific paper. Comparing them is hard, but it's patently absurd to say there's nothing being produced compared to scientific papers.
ajkjk 1 days ago [-]
Dunno who you're arguing with, I didn't say they didn't produce anything of value. I said they aren't producing scientific papers. Conversations are not like papers. The scientists have conversations (sometimes on mailing lists!) as well. The analog to scientific papers in the Linux world are... scientific papers. And the occasional essay on the mailing list, which---get this---would be more valuable to humanity if it was subsequently reproduced as a paper with references and explanations and the like.
(Notwithstanding the absurdity of academic publishing, of course.)
1 days ago [-]
matthewdgreen 1 days ago [-]
If I had the email address of every researcher in my field, I would never send a mass email to them describing my latest goofy idea. I would, however, send my latest goofy idea to a conference with those same reviewers (if I felt it was technically appropriate and correct.)
XorNot 1 days ago [-]
I mean we use to have newsgroups which basically implemented this.
Which of course is the point: it is in fact quite similar to a mailing list, just with some extra protocol surounding it to make it manageable.
So the attempted snark about it up thread is stupid.
IAmBroom 8 hours ago [-]
Still inaccurate.
A paper has a (semi-formal) structure, including TITLE, AUTHORS, and the all-important ABSTRACT.
Email guarantees none of those.
baq 19 hours ago [-]
It’s a special purpose mailing list. The value (your motivations for asking notwithstanding) is in the special purpose, not in the mailing list.
colechristensen 1 days ago [-]
Instead of reading everybody's spam or having to have a centralized body decide who gets to send messages to the mailing list, journal editors filter which things are worthy of publication and in which journal such that readers don't have to wade through garbage or uninteresting results.
smueller1234 1 days 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.
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..."
dguest 18 hours ago [-]
Unfortunately it wasn't just the public: it caused so much uproar within the experiment that two of the highest ranking members resigned their posts [1].
I was a bit dismayed at the reaction within the physics community. Experiments absolutely do need to follow procedures like blinding and careful internal review (especially before the data unblinding), but you can only spend so long designing the analysis before you unblind, and there are opportunity costs to cross checking everything. In an optimized community experiments will inevitably make mistakes. And once you unblind, it does no one any good to sit on an anomalous result forever.
That was a fiendish thing to debug; if I recall correctly it was a slightly and intermittently defective connector.
dd8601fn 1 days 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 1 days 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 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 8 hours 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.
logdahl 1 days ago [-]
Wow haha, that is a lot of authors! Never seen this before!
I think the final COVID consortium report has something like 30k authors.
alexpotato 1 days 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).
GuB-42 13 hours 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 4 hours 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.
15 hours ago [-]
derektank 1 days ago [-]
Are there any other candidate particles besides WIMPs that the observation could be from, assuming it’s a real signal?
SaberTail 1 days 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 1 days 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 1 days 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.
Nevermark 1 days ago [-]
The experiment is set up to make any already understood interactions some combination of easy to identify or extremely improbable.
SaberTail 1 days ago [-]
They have a lot of shielding for the detector, and also if there were a significant source of neutrons they'd expect to see other evidence, both in the detector and in the separate "veto" detector that surrounds the main detector.
That's not to say it can't be a neutron, but it would be surprising if it were.
antonvs 1 days 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 9 hours 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 8 hours 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?
pizzathyme 1 days 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.
petcat 1 days 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.
butlike 6 hours 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?
gwbas1c 1 days 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.
strogonoff 22 hours 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 20 hours 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 19 hours 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.
retsibsi 14 hours ago [-]
> The map has to be become the territory for genuinely perfect accuracy.
Why couldn't the territory be losslessly compressible?
narnarpapadaddy 13 hours ago [-]
The currently accepted answer to that is “the territory appears to be randomized” (quantum mechanics)
retsibsi 13 hours ago [-]
Makes sense, but is it relevant to the upthread claim that "All provable models (theories, explanations) that we have, or could have, are by definition wrong or incomplete"? (Not being rhetorical and snide here, I'm curious and aware I may be missing something.)
If reality has irreducible randomness (an open question afaik), and we're talking about theories and explanations (so we're not necessarily trying to describe the actual state of every particle in the universe, but only the rules governing their interactions), couldn't we have a complete, correct theory that was much smaller than the universe and contained terms for the random elements?
There would always be the possibility that it would turn out to be wrong, but it could be complete and correct, so it seems like the original claim must depend heavily on the word 'provable' and not on the impossibility of describing a system via a map smaller than the territory.
edit: but also, surely 'the territory is randomized' is a contingent physical fact, and not a necessary truth of information theory. Until we know for sure that there is irreducible randomness, we can't know that the information content of the universe (including the actual state of all particles at all times) isn't losslessly compressible, right?
narnarpapadaddy 10 hours ago [-]
The “elements for randomness” are carve-outs for the parts of territory the map can’t contain. The more granular the map, the larger relative proportion that falls into that set. Nobody can predict the layout of my basement from a globe of the world.
We know with a high degree of certainty the universe contains things we can’t predict or observe, see Bell’s Theorem.
“Truth” doesn’t exist outside reality. There’s no substrate to hang it in. Information theory is likewise a subset of the territory, part of the universe, not apart from it. For these things to exist independently, you need something other than or bigger than the universe to put them in. If such a thing existed, sure, from that perspective maybe a lossless compression could exist. But that’s a metaphysical argument.
BurningFrog 1 days ago [-]
Astronomy/Physics is overflowing with unexplained physics phenomena these days.
Especially after JWT started looking deeper into the early universe.
naasking 12 hours ago [-]
They detected a single weird event, not necessarily a particle.
1 days ago [-]
lordnacho 1 days 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 1 days 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 1 days 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-proce...
cogman10 1 days 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.
cwmma 1 days ago [-]
Probably not, they have a pretty good handle on why atoms decay, to the point they can predict some to be radioactive before it's actually observed to be (like Bismuth-209).
Also even if something is REALLY REALLY long lasting, you can still check for the halflife by observing enough of it, they've been able to rule out proton halflives under 10^34 years (the universe is on the order of 10^10 years old) but by observing enough protons (like say 50,000 tons of water) you would expect at least some to decay.
cogman10 1 days ago [-]
> they have a pretty good handle on why atoms decay
Oh, they actually don't. Radioactive decay, AFAIK, is still an open physics mystery. We know it happens, we don't know why, what causes it, or if there even is a cause. We can predict factors that make it more likely.
> to the point they can predict some to be radioactive before it's actually observed to be (like Bismuth-209).
Right, but Xenon 124 wasn't predicted to be radioactive which is what makes it fascinating. It shows holes in what we can predict as being radioactive which is what makes me wonder about everything being radioactive but the timetable is too far out.
cwmma 10 hours ago [-]
I don't actually think Xenon-124 being radioactive was a surprise. All the publicity related to observing the decay for the first time is phrased around 'hey we observed something that's very rare' not 'hey this thing happened we didn't expect to happen'.
Which seems to point even more towards, scientists have a pretty good handle on which ones are radioactive.
mr_mitm 1 days ago [-]
Where is the mystery? Any system can spontaneously transform into a new state with a probability greater than zero unless some conservation law prevents it. In a sense it's just quantum tunneling.
baq 19 hours ago [-]
The mystery is the details, not in that it happens at all. Feel free to submit a paper if you have all the answers.
mr_mitm 19 hours ago [-]
Can you be more specific? I believe quantum mechanics explains all of radioactive decay. Unless the GP meant that QM is mysterious, I don't understand the problem.
baq 18 hours ago [-]
I mean questions like could you predict the decay of Xe-124 correctly? AFAIK theory overestimates the rate
mr_mitm 17 hours ago [-]
Quantum Chromodynamics, path integrals, and what other mechanisms you need for deriving the half life are extremely complicated, especially for that many particles, so of course it's hopeless without approximations, which can be wrong, or are even wrong by definition. But the fact that it's prohibitively hard to solve the equations for such complicated systems doesn't indicate a gap in our understanding. You don't even have to go to xenon, this is already the case for tritium.
marcosdumay 1 days ago [-]
There's just no way deuterium is radioactive, unless hydrogen is radioactive too.
gus_massa 1 days ago [-]
Some theories predict that protons decay, but the half life is like 1E31 or 1E35 years (compare to the Xe124 that has a half life of only 1E24 years). All experiments so far to measure the proton decay have failed, anyway. https://en.wikipedia.org/wiki/Proton_decay
I don't remember anything specific about deuterium, and the method that Xe124 uses is not available, and I can't imagine a razonable alternative method, so my guess is that deuterium is as stable as protons.
pfdietz 1 days ago [-]
Those double beta decays are also interesting because they can probe whether the neutrino is a Majorana particle.
Xe-124, half-life 1.1 * 10^22 years. That's crazy.
martinpw 1 days ago [-]
Yeah, it's funny, for experiments like this you spend 90% of your time modeling and subtracting noise, and 10% analyzing the signal that results. Had the same experience in X-ray astronomy. 3 years building a detailed model of all the sources of noise, then subtracting it out and finally starting on the science.
wuliwong 1 days ago [-]
I worked a little on the Virgo interferometer, I would say about 99.9% of the work on those types of detectors is limiting and subtracting noise. ( ≧ᗜ≦)
hirshi 23 hours ago [-]
How many years until we've discovered "everything"?
jesse_dot_id 21 hours 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 15 hours 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.
jesse_dot_id 10 hours ago [-]
I cite it because we're barely scratching the surface of our own world, which is one of a potentially infinite number of worlds that is encapsulated by the word "everything."
Why would we map the seafloor is an insane question that immediately invalidates all other opinions that you may have, unfortunately. The human embodiment of that meme with the pickaxe guy walking away from a diamond strike if only he had swung once more.
It's so hubristic to assume that our generation is the one that will discover the answers to everything.
kypro 7 hours ago [-]
> I cite it because we're barely scratching the surface of our own world, which is one of a potentially infinite number of worlds that is encapsulated by the word "everything."
I think maybe I was assuming the parent was referring specifically to physics discoveries while you were assuming that they were asking more broadly about how many years until we've discovered everything discoverable?
Unless you are actually arguing there's likely lots of physics discoveries to be made because humans have only photographed a fraction of trees on the earth, or mapped a fraction of the seafloor, or sequenced only a fraction of the genomes of known species?
ourmandave 14 hours 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 12 hours ago [-]
[dead]
sph 17 hours ago [-]
May I strongly suggest you to read Asimov’s short story The Last Question for an answer.
tl;dr: likely as long as the lifespan of the universe.
vasco 21 hours ago [-]
You can know all the whats and hows and still have no clue about why
rajaravivarma_r 1 days ago [-]
I always wondered if it would happen in my lifetime. Hope it turns out to be something interesting (AKA) dark matter.
1 days ago [-]
advisedwang 1 days 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?
evanb 15 hours ago [-]
Maybe there are even dark scientists trying to explain the missing 15% of the universe! One such scientist, easily pegged as a kook, suggests a model with SU(3) x SU(2) x U(1) gauge symmetry, with one sector spontaneously broken by a scalar field, and three flavors of fermions to allow for enough CP violation and masses spanning 10 or 11 orders of magnitude.
isomorphic 1 days ago [-]
I've heard this referred to as a "dark sector", or "hidden sector":
The scary thought is that, were it true that there is voluminous richly-interacting dark matter, we would be the actual dark sector.
kstrauser 1 days ago [-]
"Imagine a universe, like ours, overlapping ours, except where some of its matter spontaneously rips itself apart, and other matter can be mashed together if you squeeze it hard enough." "That's nightmare fuel! Fortunately it's probably impossible, so far as we can tell."
I can imagine other scary thoughts, though. Ever read any Warhammer lore?
clarionbell 18 hours ago [-]
Good news: we have discoverd FTL! Bad news: the ship came back *wrong*.
hyperhello 1 days 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 1 days 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.
stouset 1 days ago [-]
Our observations are much more consistent with a form of dark matter which does not self-interact, or which does so incredibly weakly.
Don’t ask me how or why, but this is essentially the universal (pun intended) consensus amongst cosmologists.
terminalbraid 1 days ago [-]
That doesn't rule out "dark matter having other interactions which do not interfere with our detectors" Dark sector theories which include other dark particles or new particle interactions are not controversial amongst cosmologists in this space. For example there's a whole area of study around "dark photons" which would mix with our photons and interact with dark matter.
1 days ago [-]
hyperhello 1 days 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.
marcosdumay 1 days ago [-]
It's very hard to explain the gravitational halo around the galaxies if your dark matter can interact with itself. If it interacted like normal matter, it would have a distribution similar to the gases, and not spread way into intergalactic space.
XorNot 1 days 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.
Why couldn't it be just a weirdly energetic neutrino originating from the neighborhood of some black hole?
physicsdude 1 days 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.
hershkumar 1 days 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 21 hours 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.
hershkumar 12 hours ago [-]
I think the WIMP interaction process via the models they tested and the data on astrophysical neutrinos from other detectors gives at least several(?) orders of magnitude of separation in the rate at which each would strike the detector. Of course this would not fully rule out the possibility that it is a stray neutrino.
procflora 1 days 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!
amemi 1 days 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.
parineum 1 days 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?
SaberTail 1 days ago [-]
Detectors like this work on exposure. They're always on (except for calibration and maintenance), waiting for events to happen. This paper was written with 2.8 tonne-years of data. That is, 4.7 tonnes of liquid xenon for a little mmore than half a year. The detector has 7 tonnes, and the 4.7 number reflects cuts they made on parts of the detector that either they don't understand as well, or have higher backgrounds.
As they better understand the detector, they can use more of that mass. They have data from it, but they just didn't use it. And they're always collecting more data, too, as time passes.
So the 3x is saying they have something like 8.5 tonne-years of data.
lofaszvanitt 1 days ago [-]
Hm, they have 7 tonnes of Xenon. Events detected all around in the matter, but the PMTs can localise where the event happened. So they can virtually segment parts of the detector where they are sure all the outside effects are understood and taken care of.
IsTom 1 days 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 1 days 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 1 days ago [-]
I think this description is essentially correct.
gus_massa 1 days ago [-]
They collected x3 more hay, and they still have to processes it and try to find any needle mixed with it.
Hopefully it the new data may have 3 additional events, or perhaps 2 or perhaps 4 or perhaps 10 or perhaps... Or the reported event may be false event caused by a lucky coincidence, and they may find 0 additional events.
evanb 15 hours ago [-]
Whether or not they've "seen" 3x more events is a little bit of a tricky question, because while they may have captured 3x the data exposure (see sibling comments) experiments often operate blinded to the data. They can develop their analysis scripts, play out various different scenarios via Monte Carlo simulation, and get their whole pipeline working without the bias of actually seeing how each change in algorithm alters the outcome for the real data.
Then, at some point, they freeze their pipeline, "open the box", run the analysis on the real data, and report what they find. But they can only "open the box" once per exposure, after that you can worry that human bias can creep in.
bronlund 9 hours ago [-]
Another particle! Who would have guessed %]
Unified-Mentor 13 hours ago [-]
[dead]
leumassuehtam 15 hours ago [-]
[dead]
sandworm101 18 hours 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.
sylware 16 hours ago [-]
This is statistical significance ! WE NEED A BIGGER DETECTOR! GI'ME MONEY!
evanb 15 hours 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.
This is 1σ. It’s fun and interesting, but means nothing.
marcosdumay 1 days ago [-]
> LZ physicists estimate there’s about a one in 200 chance the event is a statistical fluke
That's more than 3σ.
wewewedxfgdf 1 days ago [-]
Such detectors will never see dark matter because it is little black holes.
throwawayffffas 1 days ago [-]
Depending on the size of the black holes these detectors can see them.
jrgirvan 17 hours ago [-]
So much money wasted on dark*
I_am_tiberius 1 days 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 1 days 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 1 days 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.
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.
Maybe you shouldn't give much credence to your intuitions if you don't really know much about the subject. Obviously experts have those simple intuitions too except they also know the details of the theories underlying it all so they can form informed opinions.
lirolero 14 hours ago [-]
> i have zero knowledge of physics
> My intuition
> I really assume
hmmmm
I_am_tiberius 11 hours ago [-]
I used these phrases to make sure nobody takes it too serious, as it's only my intuition, as written.
lirolero 8 hours ago [-]
hmmm
BigTTYGothGF 1 days ago [-]
400 years ago you'd be saying the same thing about heliocentrism.
stefangordon 1 days ago [-]
“constant missing in our math” is roughly how inventing new particles in physics works.
When your equations are missing a number to work, you announce a new particle.
antonvs 1 days ago [-]
> I just can't believe something like dark matter exists.
That's a lot like a blind person saying they can't believe light exists.
It takes only a small amount of knowledge of physics to understand why and how dark matter might be possible, even likely. So small, in fact, that I can describe it in this comment.
The tl;dr is that all the senses you experience - sight, touch, smell, taste, and hearing - depend on the electromagnetic (EM) interaction. Touch, smell, taste, and hearing all depend on how electrons interact, and sight depends on how photons interact with electrons. But EM is only one of four fundamental interactions that we know of. We humans are essentially blind to all the others, without using devices to detect their presence.
But using devices we've invented, we can detect all sorts of things that we can't detect directly with our senses. X-rays and gamma rays, for example. But those are still just high-energy photons, not a different kind of particle altogether. They just help illustrate how limited our senses are.
A better example is the neutrino. They're pretty close to being "dark matter," because they don't interact via electromagnetism. As a result, they can pass right through your body, because there's nothing much to stop them. You're just as invisible to a neutrino as a neutrino is to you. It's estimated that about 100 trillion neutrinos pass through your body each second.
But neutrinos aren't perfectly "dark" - although they don't interact with electromagnetism, they do interact via the weak nuclear interaction, which is mostly something that happens inside the nuclei of atoms. (They also interact via gravity, but they have very small mass, so that doesn't help us detect them.)
We can detect neutrinos by building huge tanks full of very pure substances like water or argon, and burying them deep underground, to shield them from other interference. We can then look for the tell-tale signs that occur when a neutrino just happens to have a direct hit on an atomic nucleus, something that doesn't happen very often because nuclei are very small. That's why we need large tanks - to increase the odds of a hit.
The IceCube neutrino detector in Antarctica (https://icecube.wisc.edu/science/icecube/) extends to 2.5 km underground, and Super-Kamiokande in Japan (https://www-sk.icrr.u-tokyo.ac.jp/en/sk/) is buried 1 km below a mountain. They're able to detect neutrinos with high confidence, because aside from the tell-tale sing we can often even relate the neutrinos they detect to astronomical sources such as supernovae and supermassive black holes.
Neutrinos show that it's possible to have matter that doesn't interact via electromagnetism, which is all but invisible to us. And not just invisible - it can pass right through us. In the case of neutrinos, we're just "lucky" that they participate in the weak nuclear interaction, so we can detect them if we try hard enough. But what if a particle didn't do that? Then you'd have real dark matter - particles that we can't detect at all, except via the energy they carry, which participates in the gravitational interaction. But it's very difficult to detect tiny particles using gravity - which is why the first place we think we've detected dark matter is at large scales, in the motion of galaxies, where the collective mass of dark matter is large enough to be detected.
With all this in mind, a question dark matter skeptics would need to answer is, why wouldn't we expect dark matter to exist? We've identified quite a large zoo of particles, and what distinguishes each of them is that they each participate differently in the different interactions that we know about. Here's a summary of the fundamental particles and their participation in the fundamental interactions - which are gravity, electromagnetism (EM), weak nuclear, and strong nuclear (the latter two are different types of interactions that happen to have very generic names):
Electron: gravity, EM, weak
Neutrino: gravity, weak
Photon: gravity, EM
Quark: gravity, EM, weak, strong
Gluon: gravity, strong
Dark matter: gravity, ?
There's no physical reason we wouldn't expect a particle like dark matter to exist. It doesn't even have to have no interaction other than gravity - it could just have a very small degree of interaction that we can't easily detect, which is what the OP experiment is counting on.
If you accept the existence of X-rays and neutrinos, then it's not very consistent to draw the line at dark matter, once you have some understanding of the physics involved.
kbelder 5 hours ago [-]
>it could just have a very small degree of interaction that we can't easily detect, which is what the OP experiment is counting on.
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.
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. Shouldn't dark matter particles be generated by, say, cosmic ray collisions? Or black hole decay?
antonvs 3 hours ago [-]
> 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.
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_Pre...
Pre-prints are basically a mailinglist where you post your paper prior to peer review.
The value over a simple mailinglist is:
1. Stable URL and citation to enable other work and discussions to cite and reference it.
2. Versioning of the paper, allowing updates to be made without having mail out the paper, while allowing everyone to find all prior versions
3. Host for a PDF and data that might be quite large
4. Centralized searchable long term archive of scientific papers
5. Scalability, arxiv gets 30,000 submissions a day, no one wants to receive 30,000 PDFs in their inbox everyday
https://www.scientificamerican.com/blog/information-culture/...
would you include all the quoted text in the reply-alls, or is that too much?
Science has too many threads to do it successfully though
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
(Notwithstanding the absurdity of academic publishing, of course.)
Which of course is the point: it is in fact quite similar to a mailing list, just with some extra protocol surounding it to make it manageable.
So the attempted snark about it up thread is stupid.
A paper has a (semi-formal) structure, including TITLE, AUTHORS, and the all-important ABSTRACT.
Email guarantees none of those.
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
Then when it comes out as measurement error, the public is all "Damn these scientists are all hype machine clowns..."
I was a bit dismayed at the reaction within the physics community. Experiments absolutely do need to follow procedures like blinding and careful internal review (especially before the data unblinding), but you can only spend so long designing the analysis before you unblind, and there are opportunity costs to cross checking everything. In an optimized community experiments will inevitably make mistakes. And once you unblind, it does no one any good to sit on an anomalous result forever.
[1]: https://www.nature.com/articles/nature.2012.10371
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.
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.
Congratulations. You've just reduced all of medical science to the Tuskegee STD experiment.
I think the final COVID consortium report has something like 30k authors.
It's stories like this that raise my p(we are in a simulation).
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.
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.
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.
That's not to say it can't be a neutron, but it would be surprising if it were.
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.
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.
Glad to see such things getting re-purposed instead of just sealed off and abandoned.
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.
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.
Why couldn't the territory be losslessly compressible?
If reality has irreducible randomness (an open question afaik), and we're talking about theories and explanations (so we're not necessarily trying to describe the actual state of every particle in the universe, but only the rules governing their interactions), couldn't we have a complete, correct theory that was much smaller than the universe and contained terms for the random elements?
There would always be the possibility that it would turn out to be wrong, but it could be complete and correct, so it seems like the original claim must depend heavily on the word 'provable' and not on the impossibility of describing a system via a map smaller than the territory.
edit: but also, surely 'the territory is randomized' is a contingent physical fact, and not a necessary truth of information theory. Until we know for sure that there is irreducible randomness, we can't know that the information content of the universe (including the actual state of all particles at all times) isn't losslessly compressible, right?
We know with a high degree of certainty the universe contains things we can’t predict or observe, see Bell’s Theorem.
“Truth” doesn’t exist outside reality. There’s no substrate to hang it in. Information theory is likewise a subset of the territory, part of the universe, not apart from it. For these things to exist independently, you need something other than or bigger than the universe to put them in. If such a thing existed, sure, from that perspective maybe a lossless compression could exist. But that’s a metaphysical argument.
Especially after JWT started looking deeper into the early universe.
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.
Also even if something is REALLY REALLY long lasting, you can still check for the halflife by observing enough of it, they've been able to rule out proton halflives under 10^34 years (the universe is on the order of 10^10 years old) but by observing enough protons (like say 50,000 tons of water) you would expect at least some to decay.
Oh, they actually don't. Radioactive decay, AFAIK, is still an open physics mystery. We know it happens, we don't know why, what causes it, or if there even is a cause. We can predict factors that make it more likely.
> to the point they can predict some to be radioactive before it's actually observed to be (like Bismuth-209).
Right, but Xenon 124 wasn't predicted to be radioactive which is what makes it fascinating. It shows holes in what we can predict as being radioactive which is what makes me wonder about everything being radioactive but the timetable is too far out.
Which seems to point even more towards, scientists have a pretty good handle on which ones are radioactive.
I don't remember anything specific about deuterium, and the method that Xe124 uses is not available, and I can't imagine a razonable alternative method, so my guess is that deuterium is as stable as protons.
Xe-124, half-life 1.1 * 10^22 years. That's crazy.
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.
Why would we map the seafloor is an insane question that immediately invalidates all other opinions that you may have, unfortunately. The human embodiment of that meme with the pickaxe guy walking away from a diamond strike if only he had swung once more.
It's so hubristic to assume that our generation is the one that will discover the answers to everything.
I think maybe I was assuming the parent was referring specifically to physics discoveries while you were assuming that they were asking more broadly about how many years until we've discovered everything discoverable?
Unless you are actually arguing there's likely lots of physics discoveries to be made because humans have only photographed a fraction of trees on the earth, or mapped a fraction of the seafloor, or sequenced only a fraction of the genomes of known species?
Just given dark matter and energy, things the standard model doesn't answer, and our evolving tools (e.g. Grace telescope, etc.).
https://users.ece.cmu.edu/~gamvrosi/thelastq.html
tl;dr: likely as long as the lifespan of the universe.
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?
https://en.wikipedia.org/wiki/Hidden_sector
The scary thought is that, were it true that there is voluminous richly-interacting dark matter, we would be the actual dark sector.
I can imagine other scary thoughts, though. Ever read any Warhammer lore?
By itself, that does not exclude the possibility of dark matter having other interactions which do not interfere with our detectors.
Don’t ask me how or why, but this is essentially the universal (pun intended) consensus amongst cosmologists.
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.
https://arxiv.org/abs/0903.0660v1
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!
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.
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?
As they better understand the detector, they can use more of that mass. They have data from it, but they just didn't use it. And they're always collecting more data, too, as time passes.
So the 3x is saying they have something like 8.5 tonne-years of data.
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.
Hopefully it the new data may have 3 additional events, or perhaps 2 or perhaps 4 or perhaps 10 or perhaps... Or the reported event may be false event caused by a lucky coincidence, and they may find 0 additional events.
Then, at some point, they freeze their pipeline, "open the box", run the analysis on the real data, and report what they find. But they can only "open the box" once per exposure, after that you can worry that human bias can creep in.
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.
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-...
That's more than 3σ.
"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 cover the ground of speculation.
[1]: https://pirsa.org/26030070
> My intuition
> I really assume
hmmmm
When your equations are missing a number to work, you announce a new particle.
That's a lot like a blind person saying they can't believe light exists.
It takes only a small amount of knowledge of physics to understand why and how dark matter might be possible, even likely. So small, in fact, that I can describe it in this comment.
The tl;dr is that all the senses you experience - sight, touch, smell, taste, and hearing - depend on the electromagnetic (EM) interaction. Touch, smell, taste, and hearing all depend on how electrons interact, and sight depends on how photons interact with electrons. But EM is only one of four fundamental interactions that we know of. We humans are essentially blind to all the others, without using devices to detect their presence.
But using devices we've invented, we can detect all sorts of things that we can't detect directly with our senses. X-rays and gamma rays, for example. But those are still just high-energy photons, not a different kind of particle altogether. They just help illustrate how limited our senses are.
A better example is the neutrino. They're pretty close to being "dark matter," because they don't interact via electromagnetism. As a result, they can pass right through your body, because there's nothing much to stop them. You're just as invisible to a neutrino as a neutrino is to you. It's estimated that about 100 trillion neutrinos pass through your body each second.
But neutrinos aren't perfectly "dark" - although they don't interact with electromagnetism, they do interact via the weak nuclear interaction, which is mostly something that happens inside the nuclei of atoms. (They also interact via gravity, but they have very small mass, so that doesn't help us detect them.)
We can detect neutrinos by building huge tanks full of very pure substances like water or argon, and burying them deep underground, to shield them from other interference. We can then look for the tell-tale signs that occur when a neutrino just happens to have a direct hit on an atomic nucleus, something that doesn't happen very often because nuclei are very small. That's why we need large tanks - to increase the odds of a hit.
The IceCube neutrino detector in Antarctica (https://icecube.wisc.edu/science/icecube/) extends to 2.5 km underground, and Super-Kamiokande in Japan (https://www-sk.icrr.u-tokyo.ac.jp/en/sk/) is buried 1 km below a mountain. They're able to detect neutrinos with high confidence, because aside from the tell-tale sing we can often even relate the neutrinos they detect to astronomical sources such as supernovae and supermassive black holes.
Neutrinos show that it's possible to have matter that doesn't interact via electromagnetism, which is all but invisible to us. And not just invisible - it can pass right through us. In the case of neutrinos, we're just "lucky" that they participate in the weak nuclear interaction, so we can detect them if we try hard enough. But what if a particle didn't do that? Then you'd have real dark matter - particles that we can't detect at all, except via the energy they carry, which participates in the gravitational interaction. But it's very difficult to detect tiny particles using gravity - which is why the first place we think we've detected dark matter is at large scales, in the motion of galaxies, where the collective mass of dark matter is large enough to be detected.
With all this in mind, a question dark matter skeptics would need to answer is, why wouldn't we expect dark matter to exist? We've identified quite a large zoo of particles, and what distinguishes each of them is that they each participate differently in the different interactions that we know about. Here's a summary of the fundamental particles and their participation in the fundamental interactions - which are gravity, electromagnetism (EM), weak nuclear, and strong nuclear (the latter two are different types of interactions that happen to have very generic names):
Electron: gravity, EM, weak
Neutrino: gravity, weak
Photon: gravity, EM
Quark: gravity, EM, weak, strong
Gluon: gravity, strong
Dark matter: gravity, ?
There's no physical reason we wouldn't expect a particle like dark matter to exist. It doesn't even have to have no interaction other than gravity - it could just have a very small degree of interaction that we can't easily detect, which is what the OP experiment is counting on.
If you accept the existence of X-rays and neutrinos, then it's not very consistent to draw the line at dark matter, once you have some understanding of the physics involved.
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.
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. Shouldn't dark matter particles be generated by, say, cosmic ray collisions? Or black hole decay?
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.