Particle Physics Blog
Saturday, 19 July 2014
Weekend Plot: Prodigal CRESST
CRESST is one of the dark matter direct detection experiments seeing an excess which may be interpreted as a signal of a fairly light (order 10 GeV) dark matter particle. Or it was... This week they posted a new paper reporting on new data collected last year with an upgraded detector. Farewell CRESST signal, welcome CRESST limits:
The new limits (red line) exclude most of the region of the parameter space favored by the previous CRESST excess: M1 and M2 in the plot. Of course, these regions have never been taken at face value because they are excluded by orders of magnitude by the LUX, Xenon, and CDMS experiments. Nevertheless, the excess was pointing to similar dark matter mass as the signals reported DAMA, CoGeNT, and CDMS-Si (other color stains), which prompted many to speculate a common origin of all these anomalies. Now the excess is gone. Instead, CRESST emerges as an interesting player in the race toward the neutrino wall. Their target material - CaWO4 crystals - contains oxygen nuclei which, due their small masses, are well suited for detecting light dark matter. The kink in the limits curve near 5 GeV is the point below which dark-matter-induced recoil events would be dominated by scattering on oxygen. Currently, CRESST has world's best limits for dark matter masses between 2 and 3 GeV, beating DAMIC (not shown in the plot) and CDMSlite (dashed green line).
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15 comments:
If only limits were the goal.
Does the hunt have any limits?
At some point they will encounter the neutrino background and then they won't be able to continue with these techniques.
As far as I know, no one knows how to get past the neutrino wall. Right?
There is this idea of directional detection that may help a little. But certainly, once we hit the neutrino wall, it will become much more difficult to improve the limits.
Muon, there's no such thing as a "neutrino wall". There's a signal of coherent neutrino-nucleus scattering, interesting in its own right. For the search of dark matter beyond that, improvements would necessarily slow down due to this signal being a background in the dark matter search. But Jester, there's no reason that it couldn't go on beyond that even without directionality -- after all, the Higgs was also discovered on top of a huge standard model background.
Anyway, already these experiments are limited by severe budget cuts more than anything else. So Robert, no reason to worry, unfortunately.
I expect that an astrophysical discovery will one day render the entire particle DM search moot.
So I don't worry; I just enjoy poking fun at the true believers, whose faith has been greatly tested lately.
MOND?
'there's no such thing as a "neutrino wall"'
The neutrino wall can be very real if your uncertainties become dominated by the systematic uncertainty in the background. Then whatever you do to your detector (baring annual modulation and directional detection) the dark matter signal (or lack of signal) is completely hidden in your lack of knowledge about the background.
Alex asks: "MOND?"
Personally, I don't think so.
I am more intrigued by billions of observed but unexplained MACHOs, which may be primordial black holes.
And 100s of billions of unbound planetary-mass "nomads" in unknown physical states, which may be primordial black holes.
And the newly discovered mystery population of astrophysical objects that is producing something roughly on the order of 10,000 fast radio bursts per day!!!
I think the DM enigma has remained an enigma for so long because it is something we have not, or only superficially, considered.
Hello Jester,
what about the WW excess ? Any take on the developing story ?
Cheers,
T.
Is there a story? It has never looked very convincing, given the large theoretical uncertainties and the fact most of the excess was at small pT. Now after arXiv:1407.4481, and arXiv:1407.4537 I think it's time move on.
A key issue, of course, in terms of hypothesis rejection or acceptance is what kind of cross section of interaction we would expect in various dark matter models.
Truly collisionless dark matter, of course, can't be detected at all, and the same cross section as neutrinos would be a plausible benchmark. But, I haven't seen a very good discussion of the expected cross section of interaction phenomenology of various dark matter models on terms that can be compared apples to apples to the direct dark matter detection exclusions. The matter axis is pretty clear, but the cross section axis, not so much.
The solar neutrino flux decays as the inverse square of the distance from the sun, so the obvious solution is to get an insane billionaire to fund construction of an underground lab on Pluto.
"The solar neutrino flux decays as the inverse square of the distance from the sun, so the obvious solution is to get an insane billionaire to fund construction of an underground lab on Pluto."
Maybe just an infertile one. People with kids like to create dynasties, but people with lots of money and no kids do all sorts of cool stuff with their estates. And, it isn't as it you'd need a manned mission. It's amazing what can be done on the cheap with the right kind of inventor crew and robots.
I consider the WIMP assumption long ruled out. Too many troubles for the Galaxy, I hate to spoil it for just a dark matter idea.
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