Thursday, September 27, 2018

Sleptons in Antarctica: 5-sigma evidence for stau-like high energy terrestrial rays

As Jitter pointed out, an extremely interesting astro-ph paper appeared yesterday:
The ANITA Anomalous Events as Signatures of a Beyond Standard Model Particle, and Supporting Observations from IceCube
The paper was promoted at Live Science and the Science Magazine:
Bizarre Particles Keep Flying Out of Antarctica's Ice, and They Might Shatter Modern Physics

Oddball particles tunneling through Earth could point to new physics
What's going on?

The LHC collider hasn't found any evidence for supersymmetry before the deadlines that looked rather likely to the optimists – and not only optimists. Your humble correspondent has sent $100 to Adam Falkowski, with some logistic help by Tobias Sander. If the SUSY had been found, the outcome of our bet would have been more exciting – $10,000 into my pocket.

But the superpartners exist at some scale – everyone who is convinced that this statement is incorrect is a moron. Maybe an easier way to find evidence for SUSY is to ignore the $10 billion collider and buy an air ticket to the chilliest continent. That's how it looks according to the paper.

Derek Fox is the lead author. Steinn Sigurðsson is an important second author (in total, there are 7 authors). Do you understand why The Reference Frame is the only website that pays tribute to the beautiful (as in "Dirac") Icelandic character ð\(=\partial_\mu \gamma^\mu\) in his name? ;-)

I've known Steinn over the Internet for many years. But according to this blog, his most famous achievement so far was that he proved that his Motl number was at most six. It means that there exists the chain of collaborators Motl-Dine-Farrar-Hogg-Blandford-Hernquist-Sigurdsson.

Now, he's been very important in an actual scientific development that is said to provide us with some evidence for supersymmetry.

ANITA, some detector in Antarctica, has recorded something like two cosmic rays with EeV energies. Just to be sure, "eV" is the electronvolt and "E" stands for "exa" which is one million times "tera" (the thing in between is "peta"). So "exa" is \(10^{18}\).

There have been other "exa-electronvolt" particles in the cosmic rays but dear Houston, we have a problem here. Cosmic rays should arrive from the Cosmos and like Heaven and the sky, the Cosmos is above us. Instead, two events arrived from the bottom, from the hell, they were going up.

Can cosmic rays penetrate through the Earth and land in the detector while going in the unusual direction "up"? Low-energy cosmic rays surely can – low-energy neutrinos are almost invisible, like ghosts. But what about high energy neutrinos, like EeV?

Mr Tau (right) and his silent, small but heavy superpartner.

Well, EeV is way above the electroweak scale, 240 GeV or so, and at these high energies, the electroweak symmetry is restored. One of the implications is that neutrinos recall their siblings, the charged leptons – they interact equally strongly. That really means "very strongly". High energy neutrinos have virtually no chance to penetrate through thousands of kilometers of rock.

Fox et al. say that the probability of a Standard Model-based explanation for these two ANITA events – and a few seemingly analogous IceCube results – is below one millionth, i.e. the evidence for the Beyond the Standard Model physics is formally above 5 sigma.

And they identify a nice supersymmetric scenario that may explain the events smoothly. Instead of the conversion of "tau neutrino to tau" (which still may explain cosmic rays going from the empty space), they suggest that the particle flying through the Earth was a stau, the superpartner of the charged tau lepton.

Their stau \(\tilde \tau_R\) – like in some regular GMSB (gauge-mediated supersymmetry breaking) models – is the NLSP (next-to-lightest superpartner), it is rather long-lived, and (when it hits a nucleon, it) decays to the tau \(\tau\) lepton (the same end product as if you have the tau neutrino from the heaven) plus the LSP, the truly invisible (lightest supersymmetric) particle that is a dark matter candidate – probably denoted not as \(\tilde \chi\) but \(\tilde G\) because it should be a gravitino in GMSB.

If you can offer an immediate explanation why stau in these models is so weakly interacting to get through Earth, I will appreciate you crash course.

Right now, Fox is hungry for more data. I mean Derek Fox or the mammal. In the entertainment industry, Fox isn't hungry at all and it – acting on behalf of Disney – sold its stake in Sky to a hungry Comcast.

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