That was Super-K, the same detector she's talking about in the video. The incident occurred in 2001 and set back the start of the data taking for them quite a bit, they were able to begin data taking by re-distributing the unaffected photo-detectors to cover the gap where the imploded detectors were. Eventually (2005/2006) they replaced all the destroyed photo-detectors and took data from then on out with a full-suite of sensors. Following this incident all Japanese experiments with these types of photo-detectors take the risk of implosion seriously and have mitigation built in to the design. Super-K has been running continously since then with some interruptions for upgrades & maintenance, and is still taking data today (as far as I'm aware).
Construction is underway on the next version of the experiment "Hyper-Kamiokdande" which is similar in design but significantly bigger. If I recall correctly Hyper-K will be two 200 kilo-tonne detectors, compared to Super-K which is a measly 50 kilo-tonne detector.
Reminds me of Neil Postman's "Amusing Ourselves to Death" (1985), in which he argues that TV as a medium is fundamentally incapable of producing anything other than entertainment. So things like news, political discussion, or any other type of educational programming can only exist on TV as a nutrition-less pantomime of the real thing.
To be a bit nit-picky, Cherenkov light typically has a wide spectrum. For water it spans the entire optical range, peaking around 350nm and dying off at longer wavelengths. So you could, for example, put dye in water such that it absorbed more blue light, but you'd still be able to observe some red light from the Cherenkov radiation escaping. But the signal would be much fainter.
Although, one further caveat, changing a materials absorption spectrum will also change it's refractive index as a function of wavelength, which will in turn effect how much Cherenkov light is emitted at each wavelength. So the situation is more complicated still.
It's kinda a complicated question. Cherenkov radiation can be produced in any medium that has index of refraction greater than 1, that's what allows the charged particle radiation to go faster than the light it produces, which ultimate is what causes the Cherenkov light. The process is not reliant on the specific molecular/chemical/whatever properties of the medium, only dependent on the index of refraction. But, the index of refraction in turn comes from polarizabilty and magnetic susceptibility of the medium. Those factors depend on both what atoms & molecules exist in the medium, but also the structure of those molecules. For example, ice and water have the some chemical composition, but slightly different indices of refraction.
One line in the piece says "Observing the direct effects of radiation, although possible, requires extraordinary circumstances.". While this is mostly true, you can actually observe radiation directly, with your own eyeballs, without any extraordinary methods. Basically all you need is a radioactive source, scintillator and a very dark room. That's how scintillation counting was done back in the day. This sort of device is called a Spinthariscope, you can find examples of them on youtube and what you see is a lot like the map in the OP. So I'd say the author did a good job.
The only neutrino detector placed in a salt mine was the IMB detector. That detector was ~10kt of water observed by ~2 thousand photo-detectors, it was located ~600meters underground. The only neutrino detector that's a mile underground was the SNO detector, which was ~1kt of water, observed by ~10 thousand photo-detectors. The SNO detector is still running today as the rechristened SNO+ experiment.
Both the IMB and SNO detectors used electron scattering to observe neutrinos, a neutrino comes in and bumps into an electron orbiting an atom, the electron & neutrino both then go flying off. The electron will usually go off in the same approximate direction that the neutrino was traveling, conservation of energy and momentum requires that. The electron, if energetic enough, emits Cherenkov radiation as it goes. Cherenkov radiation is just the light equivalent to a sonic-boom, it is emitted in a cone centered around the electrons direction of travel. The light from that cone is detected by the photo-detectors. Crucially, both the interaction process (electron-scattering) and the detection process (Cherenkov radiation) will preserve the directionality from the original neutrino (for the most part). The pattern of photo-detectors that gets hit by the Cerenkov light can be analyzed to reconstruct the Cerenkov cone and estimate the original neutrinos direction. Here's an example of an observed Cerenkov ring at the Super Kamiokande detector, although this example is very clear, the Cerenkov rings aren't always so obvious.
https://cerncourier.com/wp-content/uploads/2016/07/CCthe1_06...
The IceCube detector is somewhat different. Their photo-detectors are buried in the Antarctic ice at various depths from ~1-2km and spread out over a roughly 1-cubic km volume, which is ~1Gt of water. I'm not exactly sure how many PMTs in total they have, I reckon its probably around 5-10 thousand. Since their PMT array is so much less dense than the previously mentioned experiments, they can only observe very high energy, very bright, light flashes. So neutrino sources that are low energy, like the Sun, are invisible to them. But, they can see sources that are very high energy, and Ice Cube's extraordinary size lets them observe interactions that are rare/infrequent, such as those from very far away galaxies.
High energy neutrinos will almost always interact via "Deep Inelastic Scattering" (DIS), which is basically the neutrino hitting the protons & neutrons within an atomic nucleus. Since DIS is a scattering process, conservation of energy/momentum requires the scattered particles will preferentially travel in the same direction that the incoming neutrino was traveling in. After that Cerenkov radiation is produced from the scattered protons & neutrons, and that Cerenkov radiation still is emitted in a cone pointing in the direction of travel. So once again, the interaction (DIS) and detection (Cerenkov radiation) preserves directional information. So the pattern of which photo-detectors observe the light can be used to reconstruct that direction, and point back to the neutrinos source (approximately).
I think you're correct to say a lot of people simplify what the problem is with neutrino mass. In principle it seems like there is no problem, you just add a mass term for the neutrino just like any other particle. Just b/c at first we didn't expect that term to be there doesn't mean it's a problem to now, or that original expectation was all that meaningful. And again, as you point out, there are a couple of potential ways to add that mass term in, either the "normal" way with a right handed neutrino, or with some fancy see-saw majorana term, or some combination thereof.
The issue is though, right now the standard model is at least ambiguous in terms of the majorana mass term. If it ends up the neutrino gets its mass from only the "normal" mass term, then why doesn't it have a majorana mass term? There's no current symmetry that says there can't be a majorana mass? If the neutrino's majorana mass is zero, then you'd probably have to introduce a symmetry into the standard model that says majorana particles can't exist.
But if the neutrino does end up having a non-zero majorana mass term then that means the neutrino is a majorana particle, and can undergo lepton number violating processes (e.g. neutrinoless double beta decay). Again, that's new physics.
So no matter how you give the neutrino mass, you're gonna have to modify the standard model in some "significant" way to accommodate. Either by specifically saying majorana particles can't exist, or by allowing for lepton number violating processes.
Now you could say, well then it might the case that majorana particles don't exist b/c that would require lepton number violating processes, so I don't need to introduce a new symmetry, I can just take advantage of one that's already lying around. That might be a valid claim to make...I'm not sure. I think the issue with that comes down to the difference between lepton number a global vs accidental symmetry in the standard model.
Articles like this always remind me of Clifford's "The Ethics of Belief". I feel like no one ever sums up the the importance of thorough and independent thought as well as Clifford did 150 years ago.
For their more recent data they reported seeing ~32000 solar neutrino events over a 1600 day dataset (cite: top-right of page 13 https://arxiv.org/pdf/1606.07538.pdf). Their detector nowadays is more sensitive than it was when the OP was published so I would estimate the image comes from probably around 5000 neutrino events.
And I don't know any specific numbers but you can be sure a large amount more of neutrinos interacted with the air/rock between the Sun and Super-K than interacted in the detector volume. But that number (whatever it is) is still tiny compared to the total flux (which is ~5 million per square centimeter per second).
And that's of just the "high energy" type neutrinos that Super-K is sensitive to. The lower energy varieties are more like 10 billion per square centimeter per second.
I think what you're seeing is either a random noise fluctuations, or perhaps a result of the coordinate system they're using for that image. If you take a look at a similar, more up to date, image from Super-K that uses more data you don't see any sort of elliptical nature. http://www-sk.icrr.u-tokyo.ac.jp/sk/physics/image/image_sola...
The detector does not "look" in any direction, it is in no way "pointed" at the sun. It records the direction of all events that occur within its volume. But once recorded they compare the direction of all events with the direction from the sun at the time of the event. The angle between the solar direction and the event direction is what makes up that image. If the neutrinos were not coming from the sun, the image would look like white-noise. Since there is a clear "peak" at the center you can make a good estimate about what fraction of events in your data set came from the sun. That amount is a direct measurement of nuclear processes going on with the sun over the course of the dataset...which is physically interesting. Here is the 1-D version of the neutrino "picture", https://i.imgur.com/7OmXXtn.png (cite: https://arxiv.org/pdf/1606.07538.pdf). You can tell quite clearly that there are many more events pointing away from the sun then are pointing back towards it. Exactly how much more is the interesting physics measurement done here.
All that being said, the specific shape of the "sun" in the image is influenced by many factors many of which are related to the detection mechanism and the detector itself...and don't tell you that much about the sun. Eventually (one hopes), detectors will improve to the point where the "shape" information of the image is reliable enough to extract interesting solar physics measurements from it.
P.S your fun thought on the detection of a fusion reactor is extremely on point. There exists a under-construction experiment in the UK called "Watchman" that hopes to detect a neutrino signature from a nuclear power plant being shut off and then being used to produce material for a nuclear weapon. The idea would be that you could observe activities of nuclear facilities in a "rouge nation". See here https://www.nytimes.com/2018/03/27/science/nuclear-bombs-ant... or here http://svoboda.ucdavis.edu/experiments/watchman/
In principle yes....although the specifics of the physics involved kinda make the question itself not well posed.
There is no hard boundary to the core of the sun. The "core" is by definition where nuclear fusion reactions occur. However, those reactions don't just stop at a certain radius...but instead just occur at a lower and lower rate. So even if you could determine with 100% precision where a neutrino came from within the sun, you would still measure some exponential-like decay as a function of radius.
But to add even more complexity there's ~10 different nuclear processes within the sun that produce neutrinos. Those processes all have different radial profiles. So even if you measure with 100% accuracy the radial profile of neutrinos associated with one or two nuclear processes...you still haven't really measure the core of the sun...you've just measured it for a few specific reactions. And for the neutrinos produced by many of the reactions this method cannot work, those neutrinos are too low in energy to provide direction information. And beyond that there are a handful of nuclear reactions that occur within the sun that don't produce neutrinos. So there doesn't really exist any way to measure the radial profile of those nuclear processes.
And this all assume you can perfectly tell where the neutrino came from within the sun, which is also impossible. There will always be some relatively poor "resolution associated with your ability to place a neutrinos origin. Here is the "hard" physics limit to your angular resolution for a relatively high solar energy neutrino...it only gets worse as the energy goes down https://i.imgur.com/h3n8c4V.png.
But getting to even that resolution is impossible b/c an interaction will only produce so many photons from Cherenkov radiation (think 100s of photons). Then it becomes a statistics problem...what's the best angular resolution you could possibly achieve given an average number of photons that's around (say) 500. It ends up the answer is "pretty good" but far from perfect. And all of that is assuming the electron scattered from the solar neutrino will travel in only one direction...that's extremely untrue, the electron will always bounce off of other electrons & atoms after scattering. This multiple-scattering leads to even worse angular resolution.
This article is quite old but a more recent measurement from the same experiment (Super-K) used a 1600 day dataset. Of that 1600 days of exposure 860 "days" were nights. So it's pretty close to half and half. (Cite: Section V-B, bottom left of page 22, of https://arxiv.org/pdf/1606.07538.pdf )
The daytime data and night time data are decoupled quite easily. Whenever an event is recorded by the detector you just make sure a timestamp is associated with the event. Then you use that timestamp to determine the location of the sun at the time of the event. If the sun is below the horizon it's "night" and if it's above the horizon it's day.
The process behind this measurement is that the neutrino hits an electron in the detector. That electron will (with relatively high likelihood) travel in the same direction as the incident neutrino. The Cherenkov radiation produced by the electron is emitted in a cone shape along the direction of travel.
The photo-detectors observe the Cherenkov light and through some well tuned algorithms the electrons direction is "reconstructed". Super-K has no doubt spent significant effort improving & evaluating their reconstruction algorithms.
Once you have the reconstructed electron direction there's almost no hope that you can reconstruct the incident neutrino direction...but that's generally okay, b/c you can usually just assume the neutrino traveled exactly parallel to the electron (i.e. directly away from the sun). But that's sometimes wrong which is (partly) why you see a lot of "fuzz" around the solar core in the image.
It's a bit of a subtle point but Majorana anti-neutrinos are still right handed chiral particle and a Majorana neutrino is still a left handed particle. So any particle-antiparticle effects from Delta-CP (or anything else) just becomes a left-right chirality effect. That behavior is built right into the term "Delta-CP", CP stands for charge-parity, meaning it's related to both a charge flip (particle to anti-particle) or a parity flip (left to right).
I used Shankar's quantum mechanics book for my first course of quntum in undergraduate. And his "Basic Training In Math" as a supplementary book in another course. And I recall being very frustrated with the total lack of explanation for many things. Often he would simply state the way things were without attempting to guide the reader's intuition. So I couldn't disagree more about the books being good for beginners. It's been a while since I've looked at either book, so I can't cite anything specific. But I know for sure that by the end of my undergrad I passionately disliked Shankar.
Construction is underway on the next version of the experiment "Hyper-Kamiokdande" which is similar in design but significantly bigger. If I recall correctly Hyper-K will be two 200 kilo-tonne detectors, compared to Super-K which is a measly 50 kilo-tonne detector.