Dark Matter - The Search Continues

As some will know, I'm a Physcist and have been involved in the construction of large scale detector systems for the search for Dark Matter and some other areas such as Neutrino Physics. As such I bring these two pre-prints to you all that are pretty fresh and interesting.

First
arxiv.org...
Which is a 'first year' data set from the DEAP-3600 experiment.

And then hot on its tail,
arxiv.org...
Which is a complementary analysis of the dataset taking into account the possible difference between Dark Matter - Proton and Dark Matter 'Nucleon' cross-sections.

The interesting part of this is that in truth, we don't know what the coupling is, or if there is a coupling at all. So it appears only fitting when discussing what the extent of our knowledge is to present the information in an increasingly relevant manner. While Iv always said the different detector materials/targets should be seen as more complimentary than as rivals to the search.

In a nutshell there are two main areas in which the search for dark matter is conducted, Spin Dependant and Spin Independent. In the Spin Dependant model, the dark matter candidate can be a heavy particle stabilized in extra universal dimensions, having Kaluza-Klein (KK) parity th dark matter particle can such have Spin 1, rather than in the Supersymmetric and non-supersymmetric (in which it is a heavy dirac fermion) case where it has spin 1/2. To perform a search with the ability to distinguish between them is to use a target material with some residual spin.

The other is Spin Independent in which you basically shoot for high mass with a spin-less target. These detectors typically have the highest sensitivity or I should really say, have a greater coverage currently assuming the coupling is spin independent.

Now this aside, the other subtlety here is that as hinted at above, the coupling between a WIMP and the proton doesn't have to be the same as the neutron, and its a good bet that it wouldn't be. SO what can we do or what can we model to take care of this difference. Well in truth its theoretical but what the second paper does is make modifications to the sensitivity curves based upon the relative coupling difference or 'suppression' for the proton and neutron and places it where near the maximum for Xenon although firmly in so called iso-spin violating space (that there is a difference between the proton and neutron coupling)

What it shows is that if dark matter does experience this difference, the two target materials, (Xenon and Argon) are far more complimentary than what the community usually discusses. Typically the Xenon experiments continuously boast about how Xenon is the best and no one should use anything else. But the two target nuclei are quite different in that the Xenon has an excess of neutrons compared to that of Argon, so the difference in mass alone becomes less important.

If this model for looking at Dark matter is more relevant than the bog standard case, it shows that Argon is a potentially more powerful target medium with greater sensitivity at high mass than Xenon for much less exposure. Now, this will be debated by the community no doubt, but its a good avenue given that the next large argon dark matter experiment (DarkSide) is in the pre-construction stages.

I thought this was interesting enough to start a thread... any comments/questions are welcome

a reply to: ErosA433

A really cool post. Thanks!

a reply to: ErosA433

Great. Can we include dark energy in this thread or is it exclusively dark matter? Thanks.

a reply to: ErosA433

the WIMP dark matter particle can be a heavy Dirac Fermion and such have Spin 1

Back in the day, spin 1 particles were bosons. I'm not trying to be snarky - term definitions change, and I've been a bit of hermit for a couple decades now, so I don't know if the term has expanded when discussing dark matter related issues.

I haven't yet looked into the links, but I plan to. You've always provided excellent things here. S&F!

a reply to: delbertlarson

Ah yes you are correct - i actually read something wrong, The SUSY WIMP and in a non-SUSY context it would be spin 1/2 for the Dirac Fermion, ill edit my post if i can.

The difference is that the particle has to be stable and thats one of the mechanisms or forms it could take. TO obtain spin 1 it would be a different type, and be a minimal extra dimensions model. I basically read the paragraph on it and joined up two lines that are infact separate. It sounded weird when i wrote it, so great catch there sir!

arxiv.org...

a reply to: Phantom423

The two things are quite different, if there are no other questions, sure, i guess we could discuss dark energy, though the search for Dark Matter and the nature of Dark Energy are two quite different topics.

a reply to: ErosA433

Personally I'm glad scientists are starting to acknowledge WIMP's probably aren't the solution:

If there is WIMP dark matter, it must be weaker than the weak interaction permits to comprise 100% of the dark matter. Additionally, the LHC should not detectably produce it.

Theorists can always tweak their models, and have done so many times, pushing the anticipated cross-section down and down as null result after null result rolls in. That's the worst kind of science you can do, however: simply shifting the goalposts for no physical reason other than your experimental constraints have become more severe. There is no longer any motivation, other than preferring a conclusion that the data rules out, in doing so.

The 'WIMP Miracle' Hope For Dark Matter Is Dead

I still think the bimetric relativity approach is likely to be correct, it solves so many problems simultaneously I find it hard to believe it's not on the right track:

a reply to: ErosA433

Thanks - just wanted to clarify what the limits were. Looking forward to this thread.

a reply to: ChaoticOrder

In the paragraph below that you quote, it does say that, the WIMP is only one model and isn't the only one that can give the same observables. Hence the above couple of options.

Interestingly the LHC not giving any hints of Supersymmetry had many people screaming "Dark Matter is Dead!" but in truth it isn't dead at all. Its is also a weird statement from the astrophysicist to call it bad science in one line and then back it up in the other, it is also somewhat odd that he points only to the LUX and Xenon results and doesn't for example touch on the low mass region and high mass, which again, is still open for WIMPs.

Its true to say, the WIMP has been ruled out, over a certain mass range... but not entirely.

The article does then say that there are other candidates or mechanisms that can give a similar result and that the search continuing is (rightly) valuable The more we know right.... or the more we know its not i should say.

a reply to: ErosA433

The search continues because it doesn't exist. It was a contrivance to explain red shift and blue shift which don't need an explanation. A much better explanation for red shift and blue shift is that space time stretches as the universe expands rather than being infinite and that as it is stretched time is moving faster at the periphery.

Jaden

a reply to: Masterjaden

Has absolutely nothing to do with dark matter.

If you are going to make statements like the above, at least refer to the correct area of research. You are probably thinking of Dark Energy... which isn't as contrived as you make out... Dark Matter was not at all contrived to explain what you state.

a reply to: ErosA433

doesn't for example touch on the low mass region and high mass, which again, is still open for WIMPs.

It seems to me if something is called a weakly interacting massive particle it needs to have a substantial mass, and it also seems to me we thought they were massive to begin with for some important reasons. So a really low mass particle doesn't seem like a very likely outcome imo. Some sort of super-WIMP seems like a more likely explanation but there are also good reasons not to hold out hope for that. I really don't think the solution will be any type of WIMP.

a reply to: ChaoticOrder

in actual terms, massive here doesn't tell you the mass range, except that it is large enough to not be relativistic by natural state of having almost no mass.

So by low mass, we don't mean not massive.

a reply to: ErosA433

The main theoretical characteristics of a WIMP are:

• Interactions only through the weak nuclear force and gravity, or possibly other interactions with cross-sections no higher than the weak scale;[6]
• Large mass compared to standard particles (WIMPs with sub-GeV masses may be considered to be light dark matter).

Weakly interacting massive particles

a reply to: ErosA433

I took a look at the papers linked in the OP, as well as the one by Vernon Barger, et al. Vernon Barger was at the University of Wisconsin back when I was a graduate student there. My major professor at the UW, David Cline, was also involved in dark matter for quite some time. Thanks for sharing.

Unfortunately I'd likely need to have some rather remedial works to get me up to speed, and I fear it would take rather long, and it appears from the Barger work that there are a plethora of these theories. One thing I've avoided is going too far into theories that don't have any experimental evidence, so I'll instead rely on your summaries of what is going on. Thanks for that, too.

I believe simpler theories are preferable to the complexity of the Standard Model, and I hope you can take a look at this one: The ABC Preon Model. To encourage a click, part of the intro is as follows:

The ABC Preon Model involves a significant philosophical departure from modern advances in high energy physics theory, in that it focuses on entities that are proposed to really exist. This is in contrast with the underpinnings of the standard model which tend to be advanced, abstract and sophisticated mathematical constructs such as a Lagrangian or a Symplectic group. While this departure likely makes it easier for lay people to understand the ABC Preon Model, ironically it makes it harder for those expert in the standard model to grasp it. In the standard model, any discussions of quarks as real physical entities must be heavily nuanced, since the essence of the standard model lies in its underlying equations and not in mental pictures of actual physical entities. The mental pictures of quarks, leptons and Feynman diagrams are really more instructional tools than the basics of the theory. In contrast, for the ABC Preon Model, the essence of the theory is the existence of proposed simple objects that are postulated to exist, which is a style of thinking that has not been popular in high energy physics for several decades.

There is substantial agreement in the experimental record with the predictions of the ABC Preon Model. The ABC Preon Model also provides a very simple basis for all known matter. Additionally, there are many predictions of the ABC Preon Model that have yet to be verified experimentally.

I hope you can take a more in-depth look at the ABC Preon Model sometime. I don't think many serous physicists are even aware of it, and I would greatly like feedback - both positive and negative. You and I had a brief discussion about neutrino cross sections as they relate to the ABC Preon Model very early in my time here at ATS, but we didn't get into any depth of discussion on the remainder of the model. Here's the link again:

The ABC Preon Model

originally posted by: ErosA433
What it shows is that if dark matter does experience this difference, the two target materials, (Xenon and Argon) are far more complimentary than what the community usually discusses. Typically the Xenon experiments continuously boast about how Xenon is the best and no one should use anything else. But the two target nuclei are quite different in that the Xenon has an excess of neutrons compared to that of Argon, so the difference in mass alone becomes less important.

Thanks for explaining all this and citing the new papers. I tried to read them but your insights helped a lot with that.

I remember wondering why there were so many dark matter experiments when I didn't really know much about dark matter research. It seemed like a binary question, we either find dark matter in the experiment or we don't, but I didn't understand the parameter space of the searches and the different capabilities of the different searches and methods. Now I understand that better and I would have assumed it was understood the searches were complimentary, but I didn't know about this idea that Xenon was best and "nobody should use anything else", so as always I appreciate your insights into a topic I'm interested in learning more about. Thanks for making this thread!

originally posted by: Phantom423
Great. Can we include dark energy in this thread or is it exclusively dark matter? Thanks.

originally posted by: ErosA433
a reply to: Phantom423
The two things are quite different, if there are no other questions, sure, i guess we could discuss dark energy, though the search for Dark Matter and the nature of Dark Energy are two quite different topics.

Agreed, from an experimentalist point of view, there's really no overlap such as a possibility of finding out something about dark energy in a dark matter direct detection experiment. I don't want to hijack the thread on dark energy because dark matter is an interesting enough topic, but I'd just like to point out that I have run across some theoretical physics ideas where dark matter and dark energy may not be as independent as they are in running a dark matter experiment, such as this idea:

Is Dark Energy Gobbling Dark Matter, and Slowing Universe's Expansion?

Dark energy appears to be devouring dark matter and slowing the expansion of the cosmos, a new study suggests...
"This is a hint — not a solid result yet — that should stimulate further observational studies," Medvedev said. "It may happen to be real, but it may well go away."

For all I know data might have already been collected to rule that model out, but if it was true then that would be an interesting relationship between dark matter and dark energy.

Back to dark matter, we keep getting these null results which remind me of an old Edison quote that is not directly applicable but is perhaps indirectly...the null results are not failures because they keep narrowing the parameter space so we know more than we did before.

I Have Gotten a Lot of Results! I Know Several Thousand Things That Won’t Work

‘Isn’t it a shame that with the tremendous amount of work you have done you haven’t been able to get any results?’ Edison turned on me like a flash, and with a smile replied: ‘Results! Why, man, I have gotten a lot of results! I know several thousand things that won’t work.’

I’ll admit if I could do it all over again Id go into physics...a field I could have enjoyed learning for the sake of learning and not just to make money.

Great post eros! I’ll read the material and try to grasp as much as I can.

a reply to: Arbitrageur

Thanks for the links. The two papers that Eros posted are taking a while to digest. I like digging though!

the concept of dark matter is based on wrong interpretation of linear mathematics.
there is no dark matter and it will never be detected...

the so called gravitational force is calculated by this equation
F = -GMm/r2
the centrifugal force
F = Mv2/r
therefore the orbiting velocity is calculated as
v = sqrt(Gm/r)


the observed rotational speed of the galaxies is shown in this picture


where A is the calculated velocity and B is the observed velocity


so... why do I say it is wrong ??

those equations are two (2) mass equations, m1 and m2, two bodies separated from each other, where they masses are clearly not penetrating each other.

the galaxies however are billions of masses, you just can't use this equations at all..
and if you want to use them, all the bodies are actually inside the whole mass of the galaxy,
therefor they all at point R0 in this picture


means they all have to have a constant orbiting velocity like the line B

if you can't see it, I can't help you at all...

Very incorrect interpretation KrzYma your reasoning is highly flawed, the calculation is actually done as an integration of test particles. Those test particles being that of the stars themselves. So once again you have no idea what it is you are talking about and under estimating the level of study that has gone into it.