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[dupe] A major physics experiment just detected a particle that shouldn't exist (nbcnews.com)
41 points by tosh 9 months ago | hide | past | web | favorite | 17 comments

Interesting, but almost certainly a systematic error. We have a lot of experiments over the last few decades detecting neutrinos, and only 2 detecting "sterile" ones (i.e. slightly too many) seems like the outlier.

(These experiments are usually buried underground or similarly crazy in their location, so if they got something wrong about the setup/geology, e.g. If the rocks are slightly radioactive, that could skew the results like this in exactly this way.)

It's definitely possible, but I just want to point out for other readers that it's not like the collaborators haven't thought about this stuff. Quoting from the article at https://arxiv.org/abs/1805.12028

> Nuclear effects associated with neutrino interactions on carbon can affect the reconstruction of the neutrino energy, E QE , and the determination of the neutrino oscillation parameters [33]. These effects were studied previously [3] and were found to not affect substantially the oscillation fit.

> All of the major backgrounds are constrained by in-situ event measurements, so non-oscillation explanations would need to invoke new anomalous background processes.


> The MiniBooNE excess of events in both oscillation probability and L/E spectrum is, therefore, consistent with the LSND excess of events, even though the two experiments have completely dif- ferent neutrino energies, neutrino fluxes, reconstruction, backgrounds, and systematic uncertainties.

The two "outlier" experiments are consistent with one another. While they might in fact have the same systematic error, that would be quite a coincidence.

4.5 sigma is not an outlier. It might still be system error of course.

I think they were saying the experiments themselves were outliers, rather than the data within them.

It could just be another Oops-Leon.

There was a plot line in The Three Body Problem where aliens sabotaged particle physics experiments to limit human technological advancement while they were making the journey to earth.

Amazing series and even friends that don’t enjoy science function enjoyed reading them.


I was just wondering what to listen to next, now that I finished the expanse series (until the next book at least). Thanks for the recommendation; I'll check it out

How can we detect something that doesn't interact with anything?

In the article it is mentioned that the ’detection’ occurs by subtraction: three types of neutrino (electron, muon, and tau) can be detected; a known number is being sent by the source and the neutrinos oscillate between the states as they travel. However the total comes up short, indicating that they are also transmuting into some other variety, nicknamed ’sterile’. Since the neutrinos we know about interact by means of gravity and the weak nuclear force, and the latter is how we detect them, it can be summarised that the missing neutrinos must have oscillated into a sterile state that does not interact through the weak force.

This is what I thought too, but the article pretty clearly states that they detected too many neutrinos, not too few.

> Both experiments have now reported more neutrino detections than The Standard Model's description of neutrino oscillation can explain the authors wrote in the paper.

I had the same question you did: if the defining characteristic of a sterile neutrino is non-interaction, how does it get detected? My best guess is that NBC's summary of the definition of a sterile neutrino is probably wrong in a some subtle way.

In short quantum stuff. With additional kinds of neutrinos, you get different patterns of oscillation, and the experiment is located at a spot were sterile neutrinos change the oscillation pattern in such a way that you get additional neutrinos, instead of less as one would expect if they would just have another classical oscillation mode.

Perhaps a good analogue is the double slit experiment, the wavefunction interferes with itself and you get more photons at the peaks, not only less at the dark patches of the interference pattern, as one would expect in case of just blocking some of the light.

Steril neutrinos really only interact via gravity. You can detect steril neutrinos by observing an excess or a deficit of active neutrinos, i.e. you could detect more than the expected number of active neutrinos due to steril neutrinos oscillating into active neutrinos but you could also detect fewer than the expected number of active neutrinos due to active neutrinos oscillating into steril neutrinos. I did not read the paper and don't know what they are measuring but it certainly could be either or even both, i.e. they could detect an excess and a deficit under differing circumstances and both could point towards the existence of steril neutrinos.

Given the source (nbc news, mainstream with basically no track record of good science reporting) I would take the language of the report with a big grain of salt.

How come when it is an electron it doesn't just stick to other matter?

It does interact. Just very weakly/infrequently. So you need lots of data, over long periods.

The comment above is probably asking about the sterile neutrino mentioned in the article:

a "sterile neutrino" that passes through matter without interacting with it

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