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Announcements like these are always thrilling, but now is the time to be cautious! The tritium contamination needed to explain what they see is *very* small, and almost as significant a potential explanation as new physics. Still, EXCITING! https://www.nytimes.com/2020/06/17/science/xenon-axions-neutrinos-tritium.html
Here's today's paper from the XENON Collaboration announcing their result.
https://www.science.purdue.edu/xenon1t/wp-content/uploads/2020/06/xenon1tlowersearches.pdf?fbclid=IwAR0DHHfLDE3MCaUDSpl-mQSEnKhxGWmRHt4e7G5yXDUTLGHk0xyD9dnEeqI
https://www.science.purdue.edu/xenon1t/wp-content/uploads/2020/06/xenon1tlowersearches.pdf?fbclid=IwAR0DHHfLDE3MCaUDSpl-mQSEnKhxGWmRHt4e7G5yXDUTLGHk0xyD9dnEeqI
And here's Figure 4 from that paper, which shows why people are so excited. They see an excess (bins vs the expected red curve) of electron recoil events –– electrons getting a kick from an interaction with something –– in the 1-7 keV range.
One *possible* explanation is a flux of hypothetical particles called axions, which fit pretty naturally into a minimal and well-motivated extension of the Standard Model. They are light and weakly interacting in the ways we usually look for. Short thread: https://twitter.com/mcnees/status/1262732658800459780
These axions might be produced in the interior of the sun, where the temperature is around 15 million K. That translates into an energy of about
(1.5 x 10⁷ K) x (8.617 x 10⁻⁸ keV/K) ≈ 1.3 keV
That fits pretty well with the peak in XENON's apparent excess!
(1.5 x 10⁷ K) x (8.617 x 10⁻⁸ keV/K) ≈ 1.3 keV
That fits pretty well with the peak in XENON's apparent excess!
BUT, the most basic version of the axion experiment likely runs afoul of other astrophysical data. And there is also a compelling explanation based on a very, very small amount of Tritium present in the detector. So small that they can't rule it out with this experiment.
(It's just a few atoms per kilogram of the xenon used in the detector!)
Luckily the next phase of the experiment should be able to resolve this. The Collaboration claims XENONnT will only need a few months to distinguish between axions and tritium at the 5σ (if the excess appears in that data). So maybe we get new physics soon! Or maybe not!
Also, there is a possible neutrino explanation! But either the number of neutrinos coming from the sun or the strength of their interactions would have to be different than what we expect, so that would also likely involve some physics beyond the Standard Model.
There was a seminar on the new result by Evan Shockley at UChicago, but it appears the video isn't up yet. When it is you can find it here:
https://efi.uchicago.edu/events/event/1361/
https://efi.uchicago.edu/events/event/1361/
Forget that NYT story I linked in the first tweet, and go read @nattyover's piece at @QuantaMagazine instead! https://www.quantamagazine.org/dark-matter-experiment-finds-unexplained-signal-20200617/
Retweeted this earlier, but here is a great thread discussing today's XENON announcement in detail. https://twitter.com/lbaudis/status/1273263913493245952
