Wednesday, May 30, 2018

Early Xenon 1T Results Find No Dark Matter

Chart via Jester at Resonaances

The early results from the Xenon 1T direct dark matter experiment have found no dark matter with an increasingly strict exclusion range:
We report the first dark matter search results from XENON1T, a 2000-kg-target-mass dual-phase (liquid-gas) xenon time projection chamber in operation at the Laboratori Nazionali del Gran Sasso in Italy and the first ton-scale detector of this kind. The blinded search used 34.2 live days of data acquired between November 2016 and January 2017. Inside the (1042±12) kg fiducial mass and in the [5, 40] keVnr energy range of interest for WIMP dark matter searches, the electronic recoil background was (1.93±0.25)×104 events/(kg × day ×keVee), the lowest ever achieved in a dark matter detector. A profile likelihood analysis shows that the data is consistent with the background-only hypothesis. We derive the most stringent exclusion limits on the spin-independent WIMP-nucleon interaction cross section for WIMP masses above 10 GeV/c2, with a minimum of 7.7 ×1047 cm2 for 35-GeV/c2 WIMPs at 90% confidence level.
Bottom line: the WIMP dark matter model is still dead. The exclusion range is slightly more strict than LUX, which Xenon 1T has replicated and hence made more robust to all manner of systemic errors.

The background only hypothesis was 79 events. The experiment detected 63 events.


As Jester explains:
What we are learning about WIMPs is how they can (or cannot) interact with us. Of course, at this point in the game we don't see qualitative progress, but rather incremental quantitative improvements. One possible scenario is that WIMPs experience one of the Standard Model forces, such as the weak or the Higgs force. The former option is strongly constrained by now. If WIMPs had interacted in the same way as our neutrino does, that is by exchanging a Z boson, it would have been found in the Homestake experiment. Xenon1T is probing models where the dark matter coupling to the Z boson is suppressed by a factor cχ ~ 10^-3 - 10^-4 compared to that of an active neutrino. On the other hand, dark matter could be participating in weak interactions only by exchanging W bosons, which can happen for example when it is a part of an SU(2) triplet. In the plot you can see that XENON1T is approaching but not yet excluding this interesting possibility. As for models using the Higgs force, XENON1T is probing the (subjectively) most natural parameter space where WIMPs couple with order one strength to the Higgs field.
In my view, the "W portal dark matter" without a Z portal or an electromagnetic charge is exceeding implausible from a theoretical perspective. 

Higgs portal mass dark matter particles are implausible because they must be very massive which is a possibility that is strongly disfavored for reasons related to the lack of the amount small scale structure (i.e. sub-galaxy level) that you would expect with a very heavy cold dark matter candidate.

In other words, Cold Dark Matter WIMPS are ruled out. This is also a big blow to supersymmetry (SUSY) theories more generally, for which WIMP dark matter candidates are expected and almost required.

Dark matter without baryonic matter interactions (e.g. truly "sterile" neutrinos), which can't be directly observed in these kinds of experiments, even in principle, are also in trouble because it is increasingly clear that some interaction between dark matter and baryonic matter other than gravity is necessary to reproduce the distributions of dark matter inferred from astronomy observations.


neo said...

axions and very light mass dark matter seems viable

is there a dark matter model u prefer?

andrew said...

axions and warm dark matter and self-interacting dark matter models aren't entirely ruled out, but I am pretty convinced that the phenomena attributed to dark matter are a quantum gravity effect that arises from graviton self-interactions, rather than being due to dark matter particles.

neo said...

graviton self-interactions sounds a lot like geons

andrew said...

A link to the concept is here: and is not unrelated.

neo said...

there were some papers which propose that "dark matter" and galaxy rotation curves could be explained as geons, which follow up papers then refute on the grounds geons leak energy

if we want to keep the standard model intact, i've posited geons as the explanation for the third peak in the CMB, primoridal black holes for weak gravitational lensing, and MOND for galaxy rotation curves.