From here.

A Single Possible Direct Dark Matter Detection

The Lux-Zepplin direct dark matter experiment has detected a single event that could be a dark matter particle (see also here). But given the immense amount of searching which drives up look elsewhere effects and the myriad other possible explanations for a single outlier data point, it is not a definitive dark matter detection yet.

From my posts on this at the link:

With this detector does that mean that the dark matter candidate would interact with the weak nuclear force?

Or some novel fifth force that has a cross-section of interaction much weaker (by factors of millions or billions or so) than the SM weak force.

The DM cross-section of interaction of atomic nuclei (and hence the weak force charge of DM particles) would have to be profoundly weaker than that of neutrinos if it is a weak force interaction, which would be surprising since every SM particle with weak force interactions has the same weak force charge.

What would even be a standard for credible detection here? 3 events? 10? When would they start calling Stockholm?

Not sure, does the paper say what statistical significance this event has?

The paper estimates the global statistical significance at 2.6 sigma, with a local statistical significance of up to 3.4 sigma. But the number of events probably isn't sufficient to determine the significance. It also depends, in part, about the details of each event and how far those details are from the expected background events on the chart in the OP. 

But given the amount of searching that has been done with multiple direct dark matter detection experiments that are all roughly similar to each other, the significance after the look elsewhere effect should be much lower than the local statistical significance.

You'd probably need a local significance of something like 10 sigma to get a global significance that meets the 5 sigma discovery threshold. Also, it isn't just 5 sigma, you also need a theoretical framework to attach the result to and replication, to be a true discovery.

So, you'd need (1) to do a lot of analysis with outside peer reviewers to rule out extremely faint backgrounds that weren't considered in the original analysis or other possible non-DM sources of this outlier data point, and (2) you'd need another experiment in addition to LZ to see it.

But, this makes funding direct dark matter detection experiments similar to LZ for the purpose of replicating this result and tuned to the parameters space where this was seen a no brainer.

Another issue is that even if the event is some non-SM particle, it doesn't necessarily follow that it is a significant component of DM.

Direct DM experiments are based upon the assumptions that the total DM mass flux and DM particle momentum can be pretty well determined from Milky Way dynamics, so you are looking at a parameter space in which DM particle mass and DM particle cross-section of interaction with nucleons trade off against each other for any given result.

This outlier data point, if it is real, points to a fairly high DM particle mass (some arXiv phenomenology papers are speculating in the 1 TeV order of magnitude). But anything much above 10 keV of mass presents real problems as a major component of DM since inferred DM distributions which are "cored" rather than "cuspy" suggest that you need much smaller DM masses to reduce the core-cusp problem, and plausible self-interaction strengths of heavy DM particles still don't solve that problem in simulations.

So, even if it is DM, it might be a type of DM particle that makes up, for example, only 1% of DM, as a DM analog to something like carbon atoms in interstellar space, while the predominant component of particle DM, as a DM analog of something like hydrogen atoms, might be too light for LZ to detect significantly due to neutrino backgrounds.

Analysis of this result in other preprints include:
https://arxiv.org/abs/2609.01475
https://arxiv.org/abs/2609.01504
https://arxiv.org/abs/2609.01592
https://arxiv.org/abs/2609.02608
https://arxiv.org/abs/2609.02775
https://arxiv.org/abs/2609.02868
https://arxiv.org/abs/2609.02823
https://arxiv.org/abs/2609.02807

If there are multiple kinds of DM particles and this is only a rare and heavy member of that set, this implies that the cross-section of interaction can be much higher (and thus, much closer to the neutrino-nucleon cross section of interaction). This is because the cross-section of interaction calculations assume that there is only one kind of DM particle, so that the actual events recorded comes from interactions with 100% of the DM flux through LZ. But if this assumption is wrong and only, for example, 1% of DM particles are massive enough for LZ to detect, then the actual cross-section of interaction implied by a given number of events is 100 times greater in that example.

If DM particles of this mass are extremely rare (the DM analog to uranium or lead, perhaps, making up only one in a million or billion DM particles) within the universe of DM particles, then perhaps the cross-section of interaction could be equivalent to the strength of the weak force interaction of SM particles.

The effective lower bound of DM particle mass that LZ can detect is about 0.2-0.5 GeV, and the signal to noise ratio starts to degrade meaningfully for DM particle masses below 10 GeV. And, there are, to repeat, strong suggestions from the inferred shape of DM distributions, that the predominant share of DM particles (assuming that they exist) should be about 10 keV or less, which is about 20,000 times less massive than DM particles that can give rise to events detected by LZ which are distinguishable from background events, and about 1,000,000 times less massive than DM particles that LZ can detect with maximum efficiency.

My suspicions

I think that this result is either a fluke in the background events (which at 2.6 sigma global significance, a global significance that I suspect is actually overstated, is entirely plausible), or a methodological error.

Even if it is, however, a genuine BSM particle, the one observed seems unlikely to be a DM particle, and particularly unlikely to be a Higgsino, which is what many of the linked papers suggest. A Higgsino is fairly tightly constrained in supersymmetry theories to have properties that this particle is unlikely to have, and might even be possible to rule out with further analysis of this particular data point.

Further, supersymmetry theories are simply not credible as theoretical frameworks in the broader sense for a variety of reasons, even though a Higgsino mass of 1.1 TeV was predicted in 2012 as the mass of a Higgsino that was the sole component of dark matter according to Hall, Lawrence J.; Nomura, Yasunori (2012). "Spread Supersymmetry". Journal of High Energy Physics. 2012: 82. arXiv:1111.4519 doi:10.1007/JHEP01(2012)082

The non-detection of any hint of a Higgsino at the LHC also casts doubt on this hypothesis, although the formal exclusions from the LHC (which is always a bit dicey because it depends on the Higgsino model used and the mass splitting between it and certain other supersymmetric particles) only go up to about 1.025 TeV.

There are also lots of strong reasons from astronomy, as I just scratched the surface of above, to think that either gravity (modified, non-perturbative, otherwise) or a fifth force, rather than dark matter particles make more sense, and that heavy dark matter particles (1 TeV or more particles that are at the fringe of what LZ and other direct detection experiments can be sensitive to), at least as a primary source of dark matter, are among the least observationally favored dark matter particle hypotheses.

This doesn't inherently rule out the possibility of a new fundamental particle, and the spectrum of composite bound quark and gluon structures, except toponium (which has a very distinct signature and set of conditions in which it can be formed) pretty much top out in the low tens of GeV, far below the 1 TeV scale. Toponium is 344-347 GeV, which is still below the TeV scale. The most massive observed atom, Oganesson (element 118), specifically its isotope Oganesson-294, has a mass of only about 274 GeV, which is still well below 1 TeV. A mass of 1 TeV would require a rather large and complex molecule (not hadron molecule, but a normal molecule made up of ordinary chemical elements), so an event like this, if being properly interpreted is not a good fit for any known fundamental particle, any known or possible hadron, any known or plausible future atom or atomic element. So, if there is a real detection of a 1 TeV mass particle, it is very much beyond the Standard Model and new physics. But even if it is real, that doesn't mean that it is an important contributor to dark matter. It could be a BSM particle with nothing meaningful to do with dark matter phenomena.

Indeed, the lack of well-motivated candidates for a 1 TeV particle with a very low cross-section of interaction with nucleons (at least no larger than the weak force coupling), makes this extraordinary claim require extraordinary proof and compels a very hard look for other explanations, especially given its only modest statistical significance so far.