XENON1T and possible dark energy detection

[Melbourne Guy]

TL;DR Summary

New research from the XENON1T collaboration suggests an unexpected result

I can't see that this recent news has been discussed on PF, but the XENON1T dark matter detection collaboration is now suggesting that it has instead detected dark energy. They openly note speculation about what may have caused these results in the paper, but I'm more wondering if it adds weight to the hypothesis that dark matter and dark energy are potentially two manifestations of the same underlying mechanism?

https://journals.aps.org/prd/abstract/10.1103/PhysRevD.104.063023

 

[PeroK]

but I'm more wondering if it adds weight to the hypothesis that dark matter and dark energy are potentially two manifestations of the same underlying mechanism?

I wasn't aware that there was such a hypothesis.

 

[DaveE]

Granted, I'm not the intended audience for Phys. Rev. D, and, I didn't read the paper, but...

Is this paper really about a result? The only reference in the abstract to a result is buried at the end of a string of "We explore the prospects for...", "...presenting the possibility that these experiments could...", "...we examine whether...". Finally, at the end, they say "This raises the tantalizing possibility that XENON1T may have achieved the first direct detection of dark energy."

OK; or it may not have. I'm having a flashback to superluminal neutrinos.

That might be the worst paper abstract I've ever read. I understand that they won't write like journalists, but they could steal a few tricks from them.

 

[Melbourne Guy]

I wasn't aware that there was such a hypothesis.

I've seen a couple of papers suggesting this recently (as in, last six months), @PeroK, but only incidentally and I did not think to bookmark them. They were trying to interpret experimental dark matter results and offered a 'two sides of the same coin' explanation, which is certainly not common from my reading of 'dark'. If I can hunt them down, I'll add them in.

I'm having a flashback to superluminal neutrinos.

Yes, instrument error rather than the Sun's tachocline creating dark energy is the more likely cause, and I've seen suggestion that this is an effect of tritium in the xenon tank.

That might be the worst paper abstract I've ever read.

We all have our skills, but I'm not sure English is the first language of the authors I'm good with words, but still find the majority of abstracts impenetrable, and wonder whether anyone not in the field really understands the acronym-laden, jargon-ridden things?

 

[ohwilleke]

Any "New Physics" findings based upon the anomalous results from the XENON1T experiment should not be taken seriously.

It is known that there were material sources of background noise that were ignored in the XENON1T data analysis that could have impacted the result. And, the experimental apparatus was dismantled before it was possible to analyze it in order to determine if those ignored background sources were creating false positives that looked like New Physics.

Alas, we can't test the most plausible "no new physics" hypothesis of tritium contamination. Why not (The block quote is from an interview with an author in the NY Times; emphasis mine)?

There might have been undetected traces of radioactive tritium (a version of hydrogen with two neutrons) in XENON1T, causing the surrounding liquid to sparkle. The XENON team worked hard to avoid this sort of noise from the beginning, Martens said. Still, he said, the tiny levels of tritium in question here would be impossible to perfectly screen out. And with XENON1T now taken apart to build a bigger future experiment, it’s impossible to go back and check.

The tritium hypothesis fits the data to a confidence level of 3.2 sigma. Joey Neilsen, a physicist at Villanova University in Pennsylvania, who is not involved in XENON, said that corresponds to about a 1 in 700 chance that random fluctuations would have produced the signal.

The half-life of tritium is 12.3 years. The experiment ran for roughly two years.As Jester (a.k.a. Adam Falkowski) at his Resonances blog explained (emphasis mine):

Experience has shown again and again that anomalies in new physics searches have, with a very large confidence, a mundane origin that does not involve exotic particles or interactions. In this case, possible explanations are, in order of likelihood, 1) small contamination of the detector, 2) some other instrumental effect that the collaboration hasn't thought of, 3) the ghost of Roberto Peccei [ed. the theorist who proposed the axion and died shortly before the results were announced], 4) a genuine signal of new physics.

In fact, the collaboration itself is hedging for the first option, as they cannot exclude the presence of a small amount of tritium in the detector, which would produce a signal similar to the observed excess. Moreover, there are a few orange flags for the new physics interpretation:

1. Simplest models explaining the excess are excluded by astrophysical observations. If axions can be produced in the Sun at the rate suggested by the XENON result, they can be produced at even larger rates in hotter stars, e.g. in red giants or white dwarfs. This would lead to excessive cooling of these stars, in conflict with observations. The upper limit on the axion-electron coupling from red giants is 3*10^-13, which is an order of magnitude less than what is needed for the XENON excess. The neutrino magnetic moment explanations faces a similar difficulty. Of course, astrophysical limits reside in a different epistemological reality; it is not unheard of that they are relaxed by an order of magnitude or disappear completely. But certainly this is something to worry about.

2. At a more psychological level, a small excess over a large background near a detection threshold... sounds familiar. We've seen that before in the case of the DAMA and CoGeNT dark matter experiments, at it didn't turn out well.

Its results remain reliable to the extent that it ruled out New Physics (since those results would merely be weakened by false positives). But, some or all of its results that have been attributed to beyond the Standard Model physics were almost surely false positives. So, it is useless for purpose of proving the existence of New Physics.

 

[Melbourne Guy]

And, the experimental apparatus was dismantled

I did not realize that, @ohwilleke, do you know if that's common for such experiments?

Its results remain reliable to the extent that it ruled out New Physics (since those results would merely be weakened by false positives).

Do you mean regarding dark matter?

So, it is useless for purpose of proving the existence of New Physics.

Agreed, though I did not expect it to have proved anything new. Suggest something new, that's possible, surely.

 

[ohwilleke]

I did not realize that, @ohwilleke, do you know if that's common for such experiments?

I don't know, but I think this was sooner than would be typical.

Do you mean regarding dark matter?

Dark matter would be one possible New Physics explanation, but not the only one. There are something like a dozen different proposed beyond the Standard Model explanations of the reported excesses over background.

Agreed, though I did not expect it to have proved anything new. Suggest something new, that's possible, surely.

FWIW, I'm using the term "proved" in the weak, colloquial sense of provide credible positive evidence supporting something new, not in the strong sense of established as scientific law with replicated five sigma evidence supported by a plausible physics based explanation.