Category Archives: Dark Matter

Edelweiss Releases New WIMP Limits

The Edelweiss experiment has released a new preprint including updated limits in the low mass region from their WIMP dark matter search using germanium bolometers. There are still some stronger limits, but one interesting thing is that this further bolsters the case that the various purported WIMP signals from other experiments are probably not actually dark matter. The results from experiments like CoGeNT, CRESST, and DAMA all lie above the limit shown here.

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Antares Looks for Dark Matter Signals

The ANTARES neutrino telescope has a new result looking for “secluded” dark matter, where dark matter annihilation is mediated through some new mediator that then decays into Standard Model particles. They claim that this can explain the high energy bump in the positron/electron ratio and can also still be a thermal relic from the Big Bang.

They look at several different channels, including one where the mediator actually lives long enough to reach Earth and decay in the atmosphere, and others where neutrinos in the final state are measured.

For this model, the result is actually stronger than direct detection experiments for spin-dependent interactions and is stronger at very high masses in the spin-independent channel. While this result isn’t particularly groundbreaking, the paper mentions that it is the first search of this kind for this type of dark matter, and I think the model, which I hadn’t heard much of previously, sounds quite interesting.

DM-Ice Releases Results

The DM-Ice experiment has released their first results for a search for an annually modulating signal of dark matter. They’re currently about an order of magnitude off from the purported DAMA/LIBRA signal but hopefully will improve significantly in the future.

DM-Ice is a NaI(Tl)-based experiment looking for signals of dark matter in their scintillating crystals. The big purpose of DM-Ice is to test various theories for why the DAMA/LIBRA experiment, a NaI(Tl) experiment at Gran Sasso, has seen an annual modulation in its event rate for many years. Various people have proposed that maybe DAMA/LIBRA is just seeing a seasonal effect. DM-Ice is in Antarctica, so any seasonal effects will be very different. If DM-Ice sees the same modulation as DAMA/LIBRA, then that would rule out many of the proposed explanation, since dark matter will modulate in the same way no matter where the detector is but most other things will be location dependent.

Sterile Neutrino Dark Matter?

There’s a new white paper/review that just appeared on the arXiv about the possibility of keV-scale sterile neutrino dark matter. I haven’t read through it, but this is an interesting non-WIMP possibility for dark matter. Sterile neutrinos don’t interact at all with the Standard Model except maybe through neutrino oscillations, but if they have mass, they can still be a dark matter candidate if there’s a good production mechanism. Current dark matter experiments would generally be insensitive to this kind of dark matter, since the standard signal of low energy nuclear recoils would probably be disallowed, or at least heavily suppressed, but there are apparently still some paths toward finding sterile neutrino dark matter beyond just discovering keV-scale sterile neutrinos.

LUX Releases Spin-Dependent Limits

While yesterday’s big news was clearly the gravitational wave result, LUX also put its first spin-dependent WIMP interaction limits on the arXiv. In direct detection experiments, the spin-independent limit is typically stronger because the amplitudes add together in coherent nuclear scattering, leading to a dependence that scales like a polynomial factor of the atomic number. Spin-dependent interactions, typically from axial vector interactions, give rise to terms related to the individual nucleons’ spins. Nucleons tend to arrange themselves so that the spins mostly cancel, so the spin-dependent terms tend to be smaller than the spin-independent terms by a factor of approximately A2 if you assume that the fundamental couplings are the same. Because the cross section ends up with some angular momentum factors in terms, you need to know the isotopic abundances very well to get a reliable spin-dependent measurement. In this result, LUX gets the best result of any direct detection experiment for WIMP-neutron spin-dependent scattering and is about an order of magnitude behind in the WIMP-proton channel (xenon is not the best nucleus to use for spin-dependent proton interactions).

Article on Snolab

Speaking of underground physics, Gizmodo has an article today on Snolab, with pictures of some of the facilities and a few detectors. Snolab is the deep underground lab in Sudbury, Ontario where a number of particle physics experiments are operating or are planned, such as SNO (and SNO+) and quite a few dark matter searches.