Weird neutrino excess won’t go away, hints at new physics | Hacker News Reader

Weird neutrino excess won’t go away, hints at new physics

arstechnica.com

79 pointsmpweiher31 comments

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A few other comment threads about this:

https://news.ycombinator.com/item?id=17210982

https://news.ycombinator.com/item?id=17225957

https://news.ycombinator.com/item?id=17253127

This one has new info, though:

Now Fermilab is back with its latest update, using two additional years of MiniBooNE data. The excess is still there, and it has edged even closer to the statistical standards for discovery. If you combine the Fermi and Los Alamos data, we're already there. It's looking more and more like another break in the Standard Model, and the possible explanations include an entirely new type of neutrino.

Given the publication dates, those other articles are almost certainly also based on https://arxiv.org/abs/1805.12028, which incorporates those two additional years of data.

> a proposed additional type of neutrino, called a sterile neutrino

Does this imply the existence of a new lepton?

Do you mean a new generation of matter, with two new leptons and two new quarks?

Cosmological data show that there should be only three generations of matter.

> Do you mean a new generation of matter, with two new leptons and two new quarks?

Yeah, that's what I was getting at: one of the leptons being the sterile neutrino and the other being the "sterile particle".

Is there a guide to science for people like me who have barely grasped Special Relativity. I am a full century out of date and I do wonder if I should be worried before we throw the stuff I don't know out and replace it with other stuff I don't know

In which case, wouldn't it just easier to wait til they figure out the new stuff ?

More seriously, if it's any consolation i spent 6 years in grad school physics and I feel like I don't understand all the particles and changing landscape when it comes to particle physics.

> I am a full century out of date

That's pretty good... when I first saw e.g. "calculus of variations" I realized I was actually at least 2 more centuries behind than I had previously thought, which was rather humbling...

Watch PBS Space Time channel starting from the early videos:

https://www.youtube.com/channel/UC7_gcs09iThXybpVgjHZ_7g/vid...

They range from easy to follow to quite technical.

It will probably be a small change. If you understand the current version it will very helpful to understand the future version.

If you imagine that elementary particles are small balls of different size and color, then it is not so difficult to understand. https://en.wikipedia.org/wiki/Standard_Model There is a lot of technical details and math, but you can get a good general understanding with the ball model. [If you ever want to propose an improvement of the standard model, you must definitively learn the technical details and math before.]

Dumb question that I feel I may have asked before, but that I don't recall the answer to:

Why does it seem like everyone believes the number of "fundamental" particles is finite? What fundamental reason is there for this?

[citation needed]

I've never seen any major institution/publication to claim the number of fundamental particles is finite. We discover new ones as we go. Nobody is really shocked these days.

I've never seen them say it explicitly, but every article I read seems to be along the lines of "physicists thought/hoped the standard model could be complete, but then this little particle came along...". Even the fact that they think they can have a model with a finite number of particles gives the impression they think this is more likely than not to be the case.

Because there is no evidence of an infinite number of different fundamental particles.

What would constitute evidence of this? The 1000th particle? 10000th? You can always argue that may be the last one.

Particles have energy levels. There is a maximum energy level and a minimum energy level. We already know that every energy level does not have a particle associated with it (quanta). Therefore there cannot be an infinite number of particles.

What would count as evidence for this?

Huh, interesting. What is the maximum energy level a particle can theoretically have? How do we know it is the maximum?

https://en.m.wikipedia.org/wiki/Absolute_hot

Tl;dr, put enough energy in a particle and it turns into a singularity.

IIRC there is some experiment where a particle split spontaneously in a pair of neutrino-antineutrino. Each type of neutrino has the same probability. In that experiment they get that only 1/3 of particles are split into "electron neutrinos", so they deduce that there are only three types of neutrinos ("electron neutrinos" / "muon neutrinos" / "tau neutrinos"). So now they are measuring another neutrino that is "sterile" for some reason doesn't appear in that experiment.

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Edit: [Perhaps more accurate] Wikipedia links to https://www.sciencedirect.com/science/article/pii/0370269389... that says:

> With the constraints of the standard electroweak model, the number of light neutrino species is found to be Nv=3.27±0.30. this results rules out of the possibility of a fourth type of light neutrino at 98% CL.

Wow. 1,959 detections out of 10^21 interactions. And they talk about statistical significance. In any other field that is so close to zero you would ignore the results.

Think of it this way: With 10^21 samples, you can be pretty certain that your sample mean will be the theoretical one.

The absolute error will be low, but the relative error can still be high. E.g. if you're dealing with events that have a frequency of 1 in 2 million, then 1 million samples can't have exactly 0.5 occurrences, so the relative error is at least 100%.

> Wow. 1,959 detections out of 10^21 interactions. And they talk about statistical significance. In any other field that is so close to zero you would ignore the results.

1959/1e21 is not the measure of the significance in the study though. That total of 1e21 interactions is split into different types of behaviors (based on theory and previous results). It's deltas on those categorized interactions and comparisons with noise/background models/characterizations that are used to assess the statistical significance of the 1959 events. I am not saying this has to be a true result and not a statistical fluke, but 1959/1e21 is not the "sigma" of this experiment.

Would a biologist dismiss the evidence of having looked at say 100 cells in a human body because there are 10^13 of them in total? The latter number has no relevance in computing significance.

Didn't even need to read the article.

When I saw the title I knew it was blown out of proportion:)

You need to compare it to the expected error rate.

If you expect for example 100 detections due to noise but you get 1000 detections in the measurement, that would be pretty significant.

Imagine you are investigating a bug you find under rocks. You have a prediction about the subvarieties this species of bug comes in. But these bugs are really hard to find. You have to turn over 10^21 rocks to find just 1,959 bugs. And you find unexpected ratios of subvarieties! The statistical significance of this unexpected result is based not on the number of rocks you turn over but on the probability your theory assigns to the distribution discovered in your sample of 1,959.

The result seems to depend critically on the researchers' estimation of the neutral current of neutral pions, which if underestimated could produce the bump in the data at the low energy range observed. I think that with further experiments this result may well fade away.

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