Biggest dark matter detector spots a single weird particle

102

rrandycupertino about 2 hours ago 16 commentsRead Article on science.org

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SaberTail•about 1 hour 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_Pre...

smueller1234•36 minutes 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

alexpotato•27 minutes 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).

derektank•26 minutes ago

Are there any other candidate particles besides WIMPs that the observation could be from, assuming it’s a real signal?

SaberTail•10 minutes 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.

pizzathyme•about 1 hour 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.

scotty79•1 minute ago

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

amemi•about 1 hour 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.

lordnacho•about 1 hour 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•40 minutes 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•10 minutes 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...

rajaravivarma_r•about 1 hour ago

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

parineum•33 minutes 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•3 minutes 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.

gus_massa•2 minutes 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.

IsTom•11 minutes 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.