# FeaturedI MiniBooNE results at 6.1 sigma: Potential evidence for sterile neutrinos

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1. Jun 2, 2018

2. Jun 2, 2018

### Orodruin

Staff Emeritus
I assume that by "IceCube" you mean "MiniBooNE".

You have to take these results with a (big) grain of salt. The best-fit they present is already ruled out by other experiments. Even more so if you consider experiments that measure different channels. In addition, the oscillation fit is still a pretty bad one. Although they have a $\chi^2/$dof of 35.2/28, many of the bins are not in the region where they have a signal and I imagine that if you would focus on that region the $\chi^2/$dof would be rather nasty. They also cover their bases on this in the last sentence of the abstract: "Although the data are fit with a standard oscillation model, other models may provide better fits to the data."

Edit: Let me also point out that Sabine has misinterpreted some of the paper in her blog post. In particular with respect to what other experiments are shown in the "money plot". Those shown are other experiments trying to measure the exact same oscillation channel. There is no way to reconcile the best-fit with OPERA even assuming sterile neutrino oscillations. Something is going on, but it is probably not sterile neutrinos.

3. Jun 2, 2018

Staff Emeritus
Also, MiniBooNE was against sterile neutrinos before they were for them.

4. Jun 2, 2018

### Staff: Mentor

Based on figure 4, they rule out $\Delta m^2 < 0.01 eV^2$ with more than 3 sigma. This means at least one neutrino mass eigenstate has to be at least 100 meV, right? 140 meV if we go by the 95% CL. And this is for the optimal case of $\theta = 45^\circ$. This could come in conflict with cosmological measurements in the not so distant future - in addition to the existing conflict with the other measurements of the same parameter.

Edit: Oops, wrong sign

Last edited: Jun 3, 2018
5. Jun 3, 2018

### kimmm

Is this interpretation correct?
LSND experimet observed and excess number of electron neutrinos,so by considering a sterIle neutrino we can explain that the muon neutrinos oscillate 5o sterile neutrinos and then theses sterile neutrinos oscillate to electron neutrinos in the short baseline experiment?

6. Jun 3, 2018

### Orodruin

Staff Emeritus
The best fit is ruled out by so many things (including the OPERA results that they show in the figure!) that I think cosmology would be one of the weaker ... It is completely incompatible with essentially everything else we know about neutrinos. Also, a state with maximal mixing is not very sterile ...

I also believe the best fit would actually already be ruled out by Planck. A "sterile" neutrino with that kind of interactions would easily thermalise and send $\Delta N_{\rm eff}$ to at least 1. And then we have not even started to talk about atmospheric and reactor neutrino experiments ...

Many would put it like this as a kind of a mental picture. However, it is a quantum process and you are never measuring the neutrino state in between production and detection so you can not say it was a sterile neutrino at some point. A more accurate way of putting it is that it would change the interference pattern among the neutrino mass eigenstates.

7. Jun 3, 2018

### kimmm

It is a very naive and basic question,but I just get confused, that all the neutrinos are like that, that they do not exist at some points, or just for sterile neutrinos?
if for others also then how we can say we have a muon neutrino beams or electron neutrinos observed by their interactions?

8. Jun 3, 2018

### Orodruin

Staff Emeritus
I did not say they did not exist. I said you do not measure their flavour state.

9. Jun 3, 2018

### kimmm

I understand,and the reason that long baseline experiments could not see any result about sterile neutrinos, is because in their baseline and their energy ranges the feature of the sterile neutrinos could not affect the probabilities of neutrino oscillation?

10. Jun 3, 2018

### Orodruin

Staff Emeritus
At longer baselines the oscillations of eV range sterile neutrinos would be completely averaged out. That does not necessarily mean you would have no information, but it would be more difficult to extract it.

11. Jun 3, 2018

### Ygggdrasil

12. Jun 3, 2018

### Staff: Mentor

@Ygggdrasil - that is primarily why I posted this in the first place. I was confused - the original title of the post reflected a popular science name 'Ice Cube', @mfb corrected me. Thanks for that.

What also confused me is why I saw nothing on PF about it except Bee H's blog, and the kinds of articles you cited.

13. Jun 4, 2018

### Orodruin

Staff Emeritus
A clear example of why one should not always trust the popular press. The NBC article does not mention that the interpretation as sterile neutrinos is in direct conflict with other experiments until pretty far down and you certainly do not get that impression from the first part of the article. The Quantamagazine article is a bit more forthcoming with this information.

You are welcome.
Also I am not sure IceCube is more "popular science" than MiniBooNE. Both are actual names of particle physics experiments. One just happens to be more known than the other.

14. Jun 4, 2018

### Ygggdrasil

Exactly why after seeing and skimming through the NBC article (mainly to see if the claims had any basis in a published article), I came here to see if you all had anything to say about the paper.

15. Jun 4, 2018

### Chronos

John Baez offers some interesting comments here: https://johncarlosbaez.wordpress.com/2018/06/02/miniboone/. The fact is MiniBooNE detected an excess of electron neutrinos over their 15 years of data collection. It isn't a huge number, but, given the confidence we have in the expected number of detections is very high, it is enough to establish a very high confidence [4.8 sigma] that something very curious is going on that is not explained by the standard model. That does not mean it is proof of sterile neutrinos, but, that is probably as good a guess as anyone has offered thus far. It should be interesting to see if MiniBooNE can nudge up the signal they currently have to up over the magic 5 sigma level with more data.

16. Jun 4, 2018

### Staff: Mentor

17. Jun 4, 2018

### Orodruin

Staff Emeritus
First of all, it is a 4.8 sigma difference with the no oscillation scenario for the best fit. This best fit happens to already be strongly excluded by other experiments, which puts the interpretation as sterile neutrinos in serious doubt. I would certainly agree that it is curious and worthy of scrutiny, but I would be very surprised if the signal is due to sterile neutrinos (see the comments I made on Backreaction).

Edit: Also, it is as good a guess as someone has offered thus far and has therefore also been much more scrutinised. It has been scrutinised to the point that it seems unlikely to be able to explain the MiniBooNE low-energy excess as oscillations just don't give a good fit of the data.

Last edited: Jun 4, 2018
18. Jun 4, 2018

### Chronos

My interest in sterile neutrinos dates back to this paper: https://arxiv.org/abs/1402.2301, Detection of An Unidentified Emission Line in the Stacked X-ray spectrum of Galaxy Clusters, which sparked an enduring controversy over the plausibility of sterile neutrinos as a component of the dark matter budget. Particle physics is not really my thing, although I have tried to keep a finger on the sterile neutrino pulse since then.

19. Jun 5, 2018

### Staff: Mentor

20. Jun 5, 2018

### Orodruin

Staff Emeritus