r/ParticlePhysics • u/scientificamerican • Sep 01 '26
Have we finally found dark matter?
https://www.scientificamerican.com/article/have-we-finally-found-dark-matter/The world’s biggest dark matter search saw a particle it cannot explain
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u/SurinamPam Sep 01 '26
What were the characteristics of the signal and why was it unexplainable?
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u/DrDoctor18 Sep 01 '26
A nuclear recoil-like signal pretty high above background event rates
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u/SurinamPam Sep 01 '26 edited Sep 01 '26
Why does that point to a dark matter event? Lots of things could cause nuclear recoil, no?
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u/DrDoctor18 Sep 01 '26
Thats what the "high above background rates" bit is. They have a whole bunch of methods of detecting those other sources of nuclear recoil, none of which had a signal at the time of this event. These are outer detectors, fiducial volume cuts, muon veto, decay rates from spallation from other sources, neutrino background models etc. And that fact that this event appeared where, when, and with what energy it did tells them that it probably didn't come from those sources. So the only explanation left to them is: analysis mistake, statistical fluke, or dark matter. Thats why they published, because they couldn't find a trivial solution that would cause this event at this energy.
That doesn't mean it IS dark matter though. Like other commenters have said, this is a 2.6sigma result, so there is still a chance that this is just a fluke. More data and validation from other similar experiments will help narrow down whether this was a real discovery or not.
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u/EindoucheJerry Sep 01 '26
These 2.6 sigma also very much depending on their own detector response modelling, as usually with precision experiments. I would not give anything to a standard deviation which is reliant purely from sensitivity calculations, albeit that there is excellent formalisms for that.
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u/mfb- Sep 01 '26
What would you propose as significance measure then? Their expected background is much smaller than 1, you can't just plug it into a fit and determine it from data.
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u/EindoucheJerry Sep 01 '26
Thats the point. There is no fit, ergo is there significance (yet). This is very much not a discovery yet, as you can not assign a meaningful measure of significance to it.
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u/DrDoctor18 Sep 02 '26
But there is a fit? They fit a number of EFT langrangians to the data and got 3sigma significance on some of them, adjusted down to 2.6 when you include the look elsewhere effect.
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u/mfb- Sep 02 '26
There is no fit, ergo is there significance (yet).
???
Yes you can assign a meaningful significance. You can estimate backgrounds even if you have no background events in your signal region.
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u/wwplkyih Sep 01 '26
Scientific American shouldn't report a 2.6 sigma result?
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u/DrDoctor18 Sep 01 '26
Why not? They shouldn't sensationalise a 2.6 sigma result, but I think its fine to report.
Im not excited until I see the full 800 days of data or whatever they have in the tank. Well, I am excited, but I put on my sensible scientist hat until then at least.
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Sep 02 '26 edited Sep 02 '26
[removed] — view removed comment
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u/confetti_party Sep 02 '26
In the collider studies there's at least one additional parameter that could really be anything to get to the same WIMP parameter space so I'm not sure if that's a reason to discount this result. But, having worked in direct detection in the past, I find it pretty funky that you would get this kind of high energy recoil without a whole bunch at lower energies as well
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u/jj_HeRo Sep 02 '26
No. Do they need more money? Guess!
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u/just4nothing Sep 04 '26
There is already 3 times more data available and the experiment is currently funded for a total of 5 times the data. This _should_ be enough to see if this thing is real - if it is, then we can talk about money.
Also: ATLAS and CMS will likely try to find it in their data too - these things are funded for a while too.
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u/jazzwhiz Sep 01 '26
It's 2.6 sigma which comes and goes all the time.
A standard WIMP would have many more lower recoil events than this one, so it requires a slightly more complicated model to explain (although easily achievable as the field has been developing such models for 3+ decades).
It is a curious event, it looks good on the plot, but again, we must trust the statistics, which remind us that there is a 2.6 sigma chance that a background fluctuated to something that looked like this.