PandaX detector finds nothing, not looking good for WIMPs

In a paper published July 12 in the journal Physical Review Letters, a team of researchers interpreted the null data from PandaX to put new limits on what dark matter could possibly be — and the work offers possible alternative explanations for what could really be out there.

The basic process of elimination reported in the paper seems pretty simple: Dark matter is unlikely to be made up of particles that interact meaningfully with ordinary matter and have masses between about 5 million and 10 million times the mass of a proton.
But that's a big deal, as Hai-Bo Yu, a physicist at the University of California, Riverside and co-author of the paper, explained.

It shows, he said, that certain proposed explanations for dark matter — most importantly, WIMPs, which should show up in an experiment on the scale of PandaX — are likely incorrect. Dark-matter particles are likely much smaller than WIMPs would have to be, he said, and may not behave in ways that make them easy to study.

"We have to be prepared for the idea that dark matter might not interact with other matter except through gravity," Yu told Live Science.

Another Dark-Matter Search Fails — Shedding Light on the Universe

Came across this piece of news yesterday and found it quite interesting because for a long time most researchers have assumed that Dark Matter must exist in the form of Weakly Interacting Massive Particles, otherwise known as WIMPs. It seems like this experiment was sensitive enough and ran for long enough that it should have detected a signal but it found nothing, indicating that the size of DM particles must be much small than we assumed, or our understanding of DM needs to be reconsidered. I like how this article highlights the fact that all of these null results tell us something about dark matter.

Is dark matter even real?

It is as real as evolution.

a reply to: howtonhawky

What you are saying is that it is complete bullhucky made up by man in an attempt to make sense of the unknown?

Also i do not trust panda's at all.

They are very deceptive creatures by the nature of their existence.

a reply to: howtonhawky



Never say no to Pandas.

This result is a publication of a short run, and is known to the community dating back to 2015. The result presented is actually surpassed by the Xenon1T experiment as I previously discussed.

Scientists have always had their minds open to the possibility that the wimp solution might not be the correct one. Or that there are parts of the model that we got wrong. I mean we are probing the unknown here. The parameter space is not fully covered however and there is plenty of scope for the next generation of large scale TPCs like PandaX and Xenon and indeed Darkside, to probe.

It could be that if the WIMP model is correct it could be spin dependant, or low mass... which means these giant detectors built thus far are less sensitive to them, not a game ending thing though, we need to cover more parameter space until we say, "Yeah... not this"

At the same time, Axion studies are really ramping up and a large scale Liquid Argon detector i worked on/built should be starting to reveal something on the order of 2-3 Tonne years of exposure... so... watch this space

a reply to: grey580

haha awesome

a reply to: ErosA433

Well this is a recent story so I thought it was worth sharing, and the research is also quite recent. If the PandaX experiment wasn't even running very long and these researchers were still able to essentially rule out WIMP type particles then it seems to me when researchers get around to analyzing the Xenon1T data properly they will reach the same conclusion with even more confidence. And how can a WIMP be low mass and massive at the same time?

a reply to: ChaoticOrder

I think the problem with the publication you referred to, is that it is based on a short period study, despite the fact that to identify a WIMP was ALWAYS going to be a a project requiring a great deal of time, tweaking of equipment, techniques and refining accuracy of the system used to detect them.

You have to assume as much, when dealing with a particle type which specifically refuses to interact with any of the things that we can actually measure easily, other than gravity of course.

a reply to: TrueBrit

It still ran long enough and is sensitive enough that it was able to place quite strong constraints on the DM particle. The Xenon1T experiment that ErosA433 mentioned seems to have imposed even tighter limits.

Experimental results from the XENON1T dark matter detector limit the effective size of dark matter particles to 4.1X10-47 square centimeters—one-trillionth of one-trillionth of a centimeter squared—the most stringent limit yet determined for dark matter as established by the world's most sensitive detector.

The results, presented Monday in a seminar in Italy at the Gran Sasso Underground Laboratory (LNGS), were produced using an active target volume of 1,300 kilograms of Xenon, the first search for dark matter that has monitored the equivalent of one ton of xenon for an entire year.

"We now have the tightest limit for what is known as 'the WIMP-nucleon cross section,' which is a measure of the effective size of dark matter, or how strongly it interacts with normal matter," said Ethan Brown, a member of the XENON Collaboration, and assistant professor of physics, applied physics, and astronomy at Rensselaer Polytechnic Institute. "With these results, we have now tested many new theoretical models of dark matter and placed the strongest constraints on these models to date."

XENON1T experimental data establishes most stringent limit on dark matter

At some point it must become so small it can no longer be called "massive" and therefore cannot be called WIMPs. But researchers have clearly become so attached to the idea of WIMPs that they find it hard to let go, even when all the data is making it very clear.

a reply to: ChaoticOrder

It's because dark matter is contrived and doesn't really exist a better explanation for blueshift and redshift is that space-time stretches as the universe expands and time increases the farther away from the origin of the universe you get.

Jaden

originally posted by: Masterjaden
a reply to: ChaoticOrder

It's because dark matter is contrived and doesn't really exist a better explanation for blueshift and redshift is that space-time stretches as the universe expands and time increases the farther away from the origin of the universe you get.

Jaden

Wonderful... your post shows you have no idea what dark matter theories say, the evidence or indeed anything else on the subject... zero points Jaden

a reply to: ChaoticOrder

It's difficult searching for DM.

This is a recent talk by Lisa Randall.



I'm not saying i support DM. No evidence so far. But. It is interesting. And. If they don't do the experiments. They never will find it.

The basic process of elimination reported in the paper seems pretty simple: Dark matter is unlikely to be made up of particles that interact meaningfully with ordinary matter and have masses between about 5 million and 10 million times the mass of a proton.
Another Dark-Matter Search Fails — Shedding Light on the Universe

originally posted by: ChaoticOrder
I like how this article highlights the fact that all of these null results tell us something about dark matter.

That article is probably the dumbest thing I ever read.

Imagine a murder investigator seeing bloody footprints leaving a crime scene and crossing a rickety bridge. He announces to his boss that he has ruled out any suspects over 10,000 pounds because that much weight would have collapsed the bridge which is still intact. His boss replies that doesn't rule out anybody because they had no suspects over 10,000 pounds.

Likewise, there are no "suspects" for WIMPS with a mass more than even 1 million times the mass of a proton that I know of, let alone 5 million times the mass of a proton or more, so ruling out masses in that range is no more helpful than ruling out murder suspects weighing more than 10,000 pounds.

Here's a graph of dark matter candidates, where the horizontal axis shows no candidates exceeding 1 million times the mass of a proton but there are many orders of magnitude of candidates below that:

WIMP dark matter candidates and searches – current status and future prospects


Fortunately the scientists are not incompetent like the science writers can often be, though this is the worst case I've seen, with other errors in the article too. The scientists did not say they ruled out candidates with masses between about 5 million and 10 million times the mass of a proton as the article claims. If you round off the mass of a proton to 1 GeV/c^2 (It's a little less than that), they say they ruled out candidates above 5 times the mass of a proton, not 5 million times the mass of a proton, so the science writer is off by a factor of about a million on that figure, and off by a factor of 1000 on the other one, and has the years of the data wrong too.

So once again, if you want to know what the scientists said, it's much better to read their paper than to read what some science writer's interpretation (or misinterpretation) says. Here is the abstract from the paper:

Constraining Dark Matter Models with a Light Mediator at the PandaX-II Experiment

We search for nuclear recoil signals of dark matter models with a light mediator in PandaX-II, a direct detection experiment in the China Jinping underground laboratory. Using data collected in 2016 and 2017 runs, corresponding to a total exposure of 54 ton day, we set upper limits on the zero-momentum dark matter-nucleon cross section. These limits have a strong dependence on the mediator mass when it is comparable to or below the typical momentum transfer. We apply our results to constrain self-interacting dark matter models with a light mediator mixing with standard model particles, and set strong limits on the model parameter space for the dark matter mass ranging from 5 GeV to 10 TeV.

So according to the paper, much of the lower end of the WIMP candidates is considered unlikely but that doesn't rule out the WIMP candidates above 10 TeV and it doesn't rule out the other dark matter candidates with a mass less than 5 times the mass of a proton (or 5 GeV to use the scientists' figures).

originally posted by: howtonhawky
Is dark matter even real?

It is as real as evolution.

It's real - it is thought to be the explanation for why stars in a distant orbit around a galaxy remain in orbit and don't fly off.

Then there is the distortion of light going through vast clouds of the stuff. It's estimated to be 42 times the mass of a proton, but doesn't interact except through gravity.

a reply to: stormcell

It's an observable phenomena. As you pointed out. The explanation for it is there, just hasn't quite been found yet.

a reply to: Arbitrageur

So according to the paper, much of the lower end of the WIMP candidates is considered unlikely but that doesn't rule out the WIMP candidates above 10 TeV and it doesn't rule out the other dark matter candidates with a mass less than 5 times the mass of a proton (or 5 GeV to use the scientists' figures).

I'm not seeing many candidates above 10 TeV on your chart there... so in other words most or all WIMP candidates have been excluded. If the DM particle exists at all, and I'm not saying it doesn't, it's quite clear they wont be in the form of WIMPs and are likely to be something much smaller, or a particle which does not interact with normal matter in any way except through gravity.

a reply to: ChaoticOrder

I read ErosA433's xenon experiment results when he posted them a couple of months back.

I'm sure he'll put me right if i get this wrong.

Although the experiment did not show wimps with the equipment and at the settings. Thy did pick something up (i think a nutrino) which they put aside for now. I don't know why. Maybe they will assess the data. Or run the experiment again at the same settings.

They will run new tests with bigger machines and different settings. Maybe they will find a wimp with the new experiments.

Even if they don't. I think the subject is very interesting. And inventing and making machines to test for these theories is really cool.

It is better to test for something and get no results than not to test at all. Imo.

a reply to: ChaoticOrder
That's a fair comment if that graph was your only source, and a lot of the WIMP space is not looking good as the title of your thread says, but remember that space is all theoretical and the edges are not sharp like they are drawn, they are uncertain and fuzzy and not the same from every source. For example, this graph Eros posted shows the parameter space for WIMPs including from way below 10 TeV up to about 100 TeV from eyeballing it, maybe even a little more than that. Eros, this is a nice graph, sorry I missed your thread at the end of May entirely until now.

www.abovetopsecret.com...

originally posted by: ErosA433
a reply to: ChaoticOrder

It is an interesting question, firstly, we have not covered the whole parameter space, we are in a rather unfortunate situation where the parameter space is fairly large. For particle dark matter It looks a bit like this

a reply to: Arbitrageur

no worries, I quite like the plot, shows how large the parameter space is haha. In the case of these searches we exclude a mass range and a cross section range. Truth is, we haven't covered all the parameter space at all, and while many of the searches are dipping their toes into parts that are not thought to be viable models the other twist of the tail is that, there are many models.

Regions which are hard to search are the low mass regions, mostly because the event kinematics are so challenging (very low energy, need very low threshold detectors, thus very susceptible to noise) These detectors are also typically very hard to build, though there are some very novel and fun designs reaching maturity. One great one is PICO, which uses a bath of supercritical liquid contained in a very smooth chamber. Particle interactions with the liquid cause it to go critical and produce a bubble. It is in effect a bubble chamber. The cool this is that before the whole liquid goes critical and boils, they recompress it. The threshold for this detector is very low, and it is fairly easy to build.

Ultimately, i think the wimp search has about 1 or 2 generations of detectors left and then the search will be over... for positive, or null. Once detectors reach the neutrino floor, things cant get THAT much more sensitive.