Monday, April 15, 2013

Dark matter direct search: CDMS suggests a light WIMP

An unexpectedly precisely suggested mass: $$8.6\GeV$$; your humble correspondent totally persuaded by the graph

For some time, I have been joining the "alerts" that it's plausible that the dark matter particle could be discovered very soon and it could be great.

In fact, there are three complementary strategies to search for the dark matter particle and there are good reasons to expect that they could provide us with some powerful evidence in favor of a specific dark matter particle rather soon: the direct production at the collider (LHC), the analyses of cosmic rays and radiation by space telescopes (AMS etc.), and the direct search experiments (germanium etc. in the abandoned mines).

It's a time for some potentially shocking news from the "third leg" of the WIMP witch hunt.

Nature blogs just told us about an APS conference that took place in Denver, Colorado on Saturday (well, it continues through Tuesday):
Dark Matter Search Results Using the Silicon Detectors of CDMS II (arXiv)

Another dark matter sign from a Minnesota mine

Official announcements and papers on the CDMS-II page (added several hours after this blog entry was initially posted)

Symmetry Magazine, Universe Today, TAMU (stories added later)

BBC, NBC News Blogs, more Google News (even later)
The relevant, loud experiment is CDMS (Cryogenic Dark Matter Search) in the Soudan Mine in Minnesota. Recall that in late 2009, CDMS informed us about two dark-matter-like events and it has placed itself among the "dark matter is seen" allies in the "is the dark matter seen?" war on the new particle's existence.

Things have apparently gotten a little bit more interesting in CDMS. Now, those eight silicon detectors have seen three events. But it's not just the number of events that is somewhat higher now. The late 2009 events could have been interpreted as background rather easily. The three new 2013 events are claimed to be substantially further from the background appearance.

While the certainty isn't enough for a formal discovery, it's being claimed that the signal is equivalent to 3+ standard deviations or so, about 99.8% confidence level. The expected background was $$0.7$$ events.

But what I find remarkable is the precision with which they dare to suggest the mass of the WIMP: it seems to be $$8.6\GeV$$. You see that it's clearly the same range as the $$7-10\GeV$$ we've discussed in the context of the "WIMP is being seen" claims for years (an unexpectedly light estimate for a WIMP mass, at least for a majority of theorists) but the indicated precision seems to be much better now. Unfortunately, they didn't include an error margin.

Amusingly enough, $$8.6\GeV$$ is also one of the two lower bounds on the WIMP mass that appear in this paper. On the contrary, you can't find this figure in the newest CDMS II paper from Friday.

These claims will be investigated by several competing experiments in the near future. XENON1T is an upgraded XENON experiment – before the upgrade, the XENON folks were staunch members of the "dark matter is not seen" axis. However, very soon, a new – and so far neutral – player could enter the war: LUX in South Dakota; see also LUX news.

In the afternoon, the experimenters released lots of details officially (including a relevant preprint) and I added this paragraph and the picture above which I find rather amazing. Does the picture convince you that the three colorful babes don't belong among the rank-and-file blue background lads but instead, they must belong to a separate hyperbola-like curve?

I am "almost" definitely convinced and I would think that if one includes all the tantalizing properties of the three events into the background-plus-WIMP hypothesis, the probability that they will agree assuming just the background will be way lower than 0.2%. We have three candidates each of which optically seems to be 3 sigmas beneath the "background cloud" and all of them sit on a hyperbola within 5 percent, with no other events differing both from the background and the hyperbola. I think that this happening by chance is really over 10 sigma.

The WIMP-nucleon cross section seems to be $$1.9\times 10^{-41}\,{\rm cm}^2$$, also very accurately determined.

Here (via Jester) you see the favored/excluded regions according to different runs of different experiments. Note that when there are lines, the experimenters claim that everything above it is excluded. XENON-10 and XENON-100 exclude a lot and contradict the parameters suggested by signals by CoGeNT and, now, CDMS. On the other hand, CDMS (the big asterisk) and CoGeNT (the purple island around it) are beautifully and nontrivially compatible with one another. CRESST with its positive claim suggests a 20% higher WIMP mass and/or cross section but it's not "totally" incompatible with CoGeNT and CDMS (a non-minimal model for dark matter could reconcile all the experiments). Given the fact that the presence of a new particle in the region seems to be a 50-50 possibility, it may be a good idea to demand the exclusions to be at 5 sigma and not 2 sigma, too. With this rule, the XENON exclusion would probably no longer contradict the positive claims while the positive claims could exceed a 5-sigma threshold for discovery in combination, too.

In Denver, some teams also talk about the searches for axions. They promise a final Yes/No verdict on axions within a few years.

By the way, string theorist Leonhard Euler would celebrate the 306th birthday today.

1. Great news, it would be cool if the dark matter hints start to converge now :-)

2. It would be awesome of dark matter was in fact several different particles of approximately equal importance.

Astronomers have implicitly assumed that all the mass in the dark sector is dominated by a single particle.

3. SO WHY did these eight silicondetectors NOT See ANY free event when they claim such exists?

Those detectors should by that be showered with events any day and night?

Or does it not happen on Earth also?

Also I am Sorry BUT calling an artificialy produced something that exists only some lausy nanoseconds a " particle" is maby daredevlish?

Also NOT any sattelite and any detector ever claimed such particles.

And believe Me when such would exist the decay of a highly radioactive 133 protonmass would exterminate all Life.

motls.blogspot.nl/2013/04/ams-02-dark-matter-is-composed-of.html

Bonusje •

Logic Insists dark matter does NOT exist. Taking that bigbangtheory THEN darkmatterforces WOULD have been strongest at the more condensed start and for that have their biggest accelerating force back then. And would decline in time and BY THAT their accelerating influence.What possibly then even would have been seen as a dé-celleration regarding gravityforces.

So I Do Think darkmatter does Not exist as a big bang universe as the hubbleconstante as quantummechanics as einstein as timespacecoupling as timegravitycoupling as gravitylenses as higgsbosons as higgsfields do Not exist As I Think higgsbosons are Not involved in gravity or in the weak force or decay.

Also as I Said below already darkmatter and Matter would drive eachother out and would each create pulled together force islands that would have produced multiple random flightdirections by force assymetry for Masses in the Universe.

More and more I get a discusting Feeling about science it all is a hoax and hoodlum with a spirit that matches the banks

4. silicondetectors NOT See ANY free event when they claim such exists?

Those detectors should by that be showered with events any day and night?

Or does it not happen on Earth also?

Also I am Sorry BUT calling an artificialy produced something that exists only some lausy nanoseconds a " particle" is maby daredevlish?

Also NOT any sattelite and any detector ever claimed such particles.

And believe Me when such would exist the decay of a highly radioactive 133 protonmass would exterminate all Life.

5. LOL, it would be nice but it surely doesn't look this way. ;-) Just the masses: this one has 8.6 GeV, Weniger sees a 130 GeV at Fermi, and AMS may suggest a 300+ GeV WIMP. Make your choice haha.

6. Right. I even think that heretical comments like yours begin to be supported by some data although it's probably too early to scream.

7. Dear Bonusje, the new three 2013 events *come* from silicon detectors at CDMS; the older two 2009 events were from germanium detectors.

These detectors are showered throughout days and nights but the cross section - the probability of interaction - is very low, namely 1.9 x 10^{-41} square centimeters. Similarly to neutrinos, the dark matter particles have extremely weak interactions - they don't interact via electromagnetic interactions and other interactions are also suppressed etc. This cross section is compatible with the theoretical calculations one may get from supersymmetric neutralinos at widely believed masses - and it implies that in several years, a detector of this size simply collects roughly three events. Get used to it.

8. it is said darkmatter got antigravity qualities so low interaction is out of the question

*Also this antigravity force as proof of interaction makes that a particle with such qualities would be Seen by all means and everytime. SO there are NO showers

In such case go search for some mistery detections and claim those to be in that darkmattertheory is some weak claim.

And what about a bit of logic?

Logic Insists dark matter does NOT exist. Taking that bigbangtheory THEN darkmatterforces WOULD have been strongest at the more condensed start and for that have their biggest accelerating force back then. And would decline in time and BY THAT their accelerating influence.What possibly then even would have been seen as a dé-celleration regarding gravityforces.

So I Do Think darkmatter does Not exist as a big bang universe as the hubbleconstante as quantummechanics as einstein as timespacecoupling as timegravitycoupling as gravitylenses as higgsbosons as higgsfields do Not exist As I Think higgsbosons are Not involved in gravity or in the weak force or decay.

Also as I Said below already darkmatter and Matter would drive eachother out and would each create pulled together force islands that would have produced multiple random flightdirections by force assymetry for Masses in the Universe.

___-_

9. Dear Crackpot, could you please reduce the rate of contamination of my blog by this incredible shit of yours at least by one order of magnitude? Thank you. You're near the edge, you piss me off once again and you're on the black list forever. Deal.

10. This is the discovery of a lifetime, Lubos, if it is real, and I do think it is real.
Boy, do I ever look forward to following this story. I can hardly contain myself :-)

11. Great to see your excitement! ;-) I would also think it's a greater discovery than the Higgs if confirmed. It's more "new", the particle is more heavenly and unusual than the Higgs which is spinless but "another rank-and-file particle that may be created in Earth labs"...

12. Dear Lubos,
two quick and potentially stupid questions:
- How do you relate this result to the recent AMS data?
The positron drop off in the AMS data if it is there can only be at a much higher energy. Would you assume that multiple dark matter particles exist?
- 8.6 GeV is well within the limit of what LHC can produce. Is it so easy for them to miss such a signal and would the precise WIMP mass help them to look for it now?

13. To be sure: are you here stil talking about darkmatter "with the famous antigravity property?

There is a lot said about dark matter and the opinions can have been changed. Therefor I ask to Confirm this property.

14. Is it possible you are just a lobbyist for that sciencebunch?

I Ask a very reasonable Question:

"To be sure: are you here stil talking about darkmatter "with the famous antigravity property?

There is a lot said about dark matter and the opinions can have been changed. Therefor I ask to Confirm this property."

IF this Question will be Confirmed then I had planned to Ask you: Why would a darkmatterparticle anyway then come to a detector when it is repelled for aeons by opposing forces of even whole galaxies and supposedly been seen in some detectors?

But I Guess you can not Answer Such Very Sane Questions is it?

darkmattertheorists say it even accelerates whole of the expansion of the Universe and by that can not even be a neutral particle. So why would such particle have a change to appear here against all opposing forces?

And beware the opposing force in Earthvincinity would then be 1 G at least.

15. have you a good link for the limits on wimps from LEP? If there were any production cross section for this it should have been seen at LEP.

16. I'd like to believe this, but what about the limits from Xenon100? The events are right near the recoil cutoff, just like '09.

17. I think that AMS refutes any blip that could be due to this 8.6 GeV hypothetical particle. But I am not sure whether it's at the level of a contradiction.

Yes, if at least two of the experimental hints are right, then we may be forced to think about multiple new, dark particles.

I believe that the 8.6 GeV particle doesn't contradict known observations from the LHC, either. These bastards are just way too invisible when produced. Quite generally, the LHC easily produces new hypothetical colored particles - gluinos, squarks - but not others. However, many particular SUSY models that would try to make this 8.6 GeV particle as a neutralino LSP are probably excluded. It's a complicated landscape where many corners are possible and many corners are no longer allowed.

18. I hhttp://en.wikipedia.org/wiki/Supernovaave this from ALEPH giving lower limit 45 GeV, so certainly a different model or parameter space would be necessary for consistency.

19. Dear Stephen, the case is strengthening that XENON folks are doing something wrong. Note that in the list of coalitions

http://motls.blogspot.com/2011/09/cresst-ii-joins-dark-matters-war-on.html?m=1

the "dark matter is not seen" really contains just XENON. They're against DAMA/LIBRA, CoGeNT, COGENT more or less Fermi and PAMELA, and now CDMS.

20. How is in this case the mass of the whole nucleus relevant for detection of the mass of an elementary particle?

21. Nice but your LEP paper clearly assumes some maximally constrained CMSSM only - this has been ruled out for almost all values of masses and the particular limit you mention is useless for the SUSY models that remain viable now.

22. Hi, I am no expert and it would be good if someone else answered.

But each element has a different sensitivity for the low masses because one has to distinguish nuclear recoils - which may be caused by a WIMP - from electron, ionization recoils that have the same final energy even from a much lower-energy bullet that hits it.

So one defines the threshold so that the discrimination is good enough and for this choice of the threshold, silicon is able to see a higher number of events than germanium. I was assuming that this superiority is sort of uniform in Z so it becomes even worse for xenon but I may be wrong.

23. Dear Mr. Motl,

Five years ago you placed in your blog
from Friday, March 21, 2008, Three preprints on cosmoclimatology, an info for
two papers later published in JASTP, 2010.

Last years I have the pleasure to read your blog – there is a lot of cool info
and discussion on topical problems. Particularly I fully share your position
about global warming and environmentalists (I have had the pleasure to receive
the autograph of Professor Vaclav Klaus after presentation of his book in
Bulgarian in Sofia, 2008).

Now, I would like to send you a link to
just published in arXive paper of Prof. Vitaliy Rusov et. al.: Axion mechanism of Sun luminosity, dark matter and extragalactic background light

http://arxiv.org/abs/1304.4127

I hope that it will be interesting for

With very best wishes,

Boyko Vachev

24. http://www.surenifty.blogspot.in/

25. Dear Mr Vachev, thanks for your kind words and your sort of tolerable advertisement of this possibly interesting paper! ;-)

26. They are assuming the WIMP can only interact with the gravitational interaction and the scattering observed is elastic. They detect the ionization and phonon secondary effect of the moving nucleus. The mass of the nucleus enters the scattering energy and momentum balance ( they assume the velocities and the probabilities, see my quote in yesterday's comment). The inertia of the nucleus itself will affect the detection probability : it has to move some distance to ionize and the ionization be detectable.

27. Sorry but I don't understand your complaint. Every paper like that has to try to impose limits and use the most acceptable figures from the state-of-the-art research to calculate those limits. And there will always be such comments in all scientific papers and they will always use data from other papers, although - hopefully - more solid and accurate ones in the future.

Moreover, this discussion of upper limits has nothing whatsoever to do with the existence of the dark matter candidates. It's an independent, one could say opposite, part of the paper.

28. I was trying to find their assumptions without digging for proposals and older publications. How did they estimate the WIMP energy input to the elastic scattering. Their assumptions are there in the quote, and even though the numbers they give are from specific fits, (not the limits plot from which the quote comes) I presume, it shows the type of distributions which are used in the fits. That is fine, but three events are not enough for so many input distributions with their widths ( and let alone errors) , at least for me.

29. It is said darkmatter got antigrav accelerating influence. SO it will never be shown in any detector on Earth against the opposing forces + 100.000 lightyears opposing gravity of a whole Milky Way. Comprende dear scientist?

30. Ow real scientific moderation? #wowsignal
I hope you are not found plagiatrising my moderated comments in the future.

31. Of course, you're totally wrong, and if you had just spent two minutes reading the very basics of the Wikipedia article on dark matter, you'd have realized that you're confusing it for "dark energy."

The original reason that dark matter was postulated was to account for apparently missing mass in large structures like galaxy clusters. The purpose of the idea was the totally opposite to antigravity.

32. That science seemingly is playing wordgames and changing postulations is not my wrongdoing.

Also the articles about the darkmatterdetectors tell it is all about exotic force and likely you missed the initial introduction of darkmatter and what claimed with it as acceleration of expansion by repellant force.

Sure it was about antigravity! Would you be so kind to explain what else could work at those distances.

If it is about missing matter no special detectors would be spoken of am I correct?

Also there are found huge masses of matter by astronomers who found regular disturbances in their telescopes what seemed passing dark objects and they guessed there might be ten times more matter then known befor.

But also that sir is not what these special detectors are about.

And where have you ever found energy that should be unrelated to matter?

Also you are disregarding ie not mentioning all other points so does that say you accept them or like with the history of the darkmatterclaims just no clue what it`s about?

So tell what one like you who seemingly is searching for normal missing matter doing here then?