Invisible Neutrino: Newsletter Challenge (June 2016)

There are no neutrino's with a mass of 14 MeV....the sum of the masses of three known neutrino flavors is 0.320 +/- 0.081 eV....

Hmm.

Found this:

http://www.sns.ias.edu/~jnb/Papers/Popular/Scientificamerican69/scientificamerican69.html

Seems the answer is:

thus the probability of capturing a 14-MeV neutrino from ⁸B decay is some 3,000 times higher than the probability of capturing a 1.4-MeV neutrino from the pep reaction.

Then there is this and this.

.

Coming up with some interesting stuff:

http://www.nap.edu/read/9185/chapter/4

Your references are all old....look at something current....

Neutrons have a mass of 14 MeV, not neutrinos.

So the question now needing clarification in this challenge is: Is this invisible particle from the sun a neutron at 14 MeV or a neutrino that started at one of the three flavors?

The sum of the masses of the 3 flavors of a neutrino is 0.320 ± 0.081 eV/c². However, the question mentions that the energy of the neutrino is 14 MeV, not the mass. Notice the difference in units: eV/c² compared to eV. Mass is measured in eV/c² and energy is measured in eV. 14 MeV is a valid energy for a solar neutrino. (Although most fusion reactions in the sun generate neutrinos that have lower energies.)

For typical solar neutrino energies, see page 45 of The Physics of Neutrinos by Vernon Barger, Danny Marfatia, Kerry Whisnant: Princeton University Press, 2012.

Would that energy be characterized as rest energy, or kinetic energy or potential energy..?....or total energy?

In The Physics of Neutrinos, the energy is described as kinetic energy. It's stated that most chains of solar fusion reactions produce neutrinos with kinetic energies in the range of 0 to 0.42 MeV, although there are some rarer reactions that produce neutrinos with energies up to 18.8 MeV.

That's from 2003....

Actually the book was published in 2012.

The book was published in 2012 but the information that you are referring to is referenced in the book from 2003...

Regardless of when the information is from, it is still accurate as the currently accepted values for solar neutrino kinetic energies. Keep in mind the question is talking specifically about solar neutrino energies, not masses. It can be confusing because particle physicists often use electronvolts as a unit for both mass and energy. (When using electronvolts for particle mass, by convention they often drop the c² in the actual units of eV/c² by setting c equal to 1.)

Physicists often drop factors of two, but to drop off c² is nothing less than lazy, and bothersome for folks that like consistency of units, as in soup.

But it doesn't really tell the reader anything -- that's to say a reader that actually has the prerequisite knowledge to understand the essay would instinctively know that c² is just a constant with units of (length/time)². I agree that if the essay was a textbook then the carefully constructed and rigid form would be more appropriate.

Right. The same professors (if they actually taught students in college classes), who write these research papers, would give the students an F for dropping off units, and factors as large as c², are all loose and fast with constants, factors, and other units, and totally sloppy, yet expect someone who doesn't read every research paper in that field to instantly follow what they are saying or be discounted as dummies.

This sort of "elitism" is nothing short of snobbery, charlatanism, and poor craft.

If they don't like it, they can come knock on my front door, and see which sound effect is active that day. Shotgun is the universal language.

Ummm... I dunno... It's not snobby IMHO, it's just shorthand for what should be implicitly understood.

If I speak of a resting proton, the reader should know the mass is ~ 938MeV. If I them mention 40GeV protons circulating in a ring, there are a few things that I simply assume the reader knows, unless I'm writing a tutorial. The protons are moving pretty close to the speed of light, but an accurate calculation of their speed can be obtained from the relativistic equation Mv=Mr/(1-v²/c²)^1/2

I would *never* speak of the 'temperature' of the particles in such a beam, because it's just a really big number that is essentially devoid of meaning., but I might use temperature to describe the tendency of those same particles to spread/scatter between steering sections, because that subtracts away toe moving frame of reference of the pulse, while humanizing the drift of the particles within the glob.

It's not lazy, it's more than just a matter of convenience, it's decluttering. It also not represent a fully formed theory... only an analogy. If I had to work out Boltzmann for the aforementioned pulse before I could say it appeared to have an internal temperature of 75K or 18,000K or higher or lower, I'd likely skip the comment.
What's really weird is I don't even know what I'm arguing anymore. You're right it is lazy, but it's accepted. Not every article has to teach, it depends on where it appears, and who the intended reader is.

I suppose so. Even with considerable math, physics background, it has been a while since I read a Modern Physics text, so things like that make it hard to follow. I would have to look up rest mass (energy) for the particles, since I no longer hold them in RAM. What my first girlfriend looked like, I have burned into PROM.

What my dad used to tell me about my worth apparently is in PROM also, but I have tried many times to treat some of those memories as EPROM.

One question: Are there neutrinos and anti-neutrinos? Could those interact with each other without charge repulsion, or other force repulsion? I am still waiting to learn if anti-matter floats up in Earth gravitational field.

May your happy memories be encoded in gates that never depolarize!

Yes, the anti-neutrino was actually the first one discovered. It's pretty weird to consider that the anti-particle of a neutral particle has the same charge... zero. Before the quark theory that was a genuine head scratcher for Neutrons.
Popular opinion tends to agree that antimatter, would still tend to fall in a gravitational field. Mass is the positive (as in absolute value) of the expression of a particle's quantum numbers. It's sign is always positive, unless the essay is considering wormholes or other esoteric phenomena. We see the effects of mass and energy, or mass-energy if you prefer, demonstrating the effects we'd expect, and there is simply no evidence to suspect that anti-matter would prove to be a source of anti-gravity.

This thread should have an interesting and possible controversial outcome. Anything dealing with neutrinos is bound to be subtle. They are ghostly at best, ephemeral, and they're damn near omnipresent.

Stephen Hawking postulated that black holes could reduce by swallowing antimatter. The theory proposed that a particle and antiparticle pair could form on the event horizon and the antiparticle could fall in. The particle could go somewhere else with the net result that mass outside the black hole would increase by the particle mass. the black hole mass would decrease by the mass of the particle.

If antimatter falls up, then the theory wouldn't work and if the quantum froth got into the habit of forming matter/antimatter pairs, then space outside the black hole would become antiparticle rich and the black hole would get more massive.

I'm looking forward to the results of the antiparticle in gravity trajectory tests.

Not certain to what you refer. When anti-matter falls into a black hole, the hole gets bigger. If a black-hole of mass M* formed out of a sufficiently large cloud of antimatter, the resulting black hole and it's normal matter counterpart collided, the resulting black hole would have a mass of 2M*. Even if the stuff that went in managed to keep some memory of it's former polarity, none of that information would escape the event horizon.

As to the evaporation of black holes and the emission of Hawking Radiation, therefrom, it is in fact due to pair production near the event horizon -- virtual particle pairs are created and annihilate on a regular basis, but every once in awhile one of the virtual particles falls into he event horizon *before* it meets it's counterpart. When a virtual pair is created out of the vacuum, virtual energy in the amount of mc² is borrowed from the void for each virtual pair, the void then has an energy deficit which is carried for a short time, that deficit is paid back to the void when the pair annihilates, a short time later. When one of the particles falls into the hole, it is no longer available to annihilate the other particle. The uncancelled particle is then free to wander away from the black hole, leaving the deficit in the region around the hole. Seen from a distance a particle has been emitted from the region in closest proximity to the hole.
Naturally, it's a very low energy particle, having given up a lot of energy by climbing out of the gravity well. But leave the hole it does, and the effect from a distance is that the black hole radiated away energy. And while the ratios are colossal, the net result is that the hole lost energy, lost mass and is a little bit smaller. That Realization won the Nobel for Hawking. It's important to point out that even the vacuum between the galaxies is so dense with matter & energy that the Hawking radiation would be undetectable.

Someday, when all the stars have gone dark, and the the cold husks of planets have evaporated into the vacuum, only then will the Hawking radiation be energetic enough to detect above the shiveringly cold background. Th4e temperature of the Hawking radiation is inversely proportional to the mass of the hole. The bigger the black hole the lower the temperature of the radiation. A 'small' stellar sized hole might radiate with a temperature of a millionth of a degree above absolute zero, a big one might be a billionth of a degree. It will take a very long time before the net flux is out and away from the hole.

you mean to tell me that a proton and an antiproton would not annihilate each other once inside a black hole? I do not think that can be correct. Or does matter stop behaving by normal quantum rules in a black hole?

The short answer is it doesn't matter if they combine and annihilate or not. When they cross the event horizon they add 1876 MeV (2*938) plus their kinetic energy to the total mass of the hole.

Say they combine inside the horizon and emit a gamma ray. That gamma ray will never emerge from the hole and will eventually smear out onto the singularity at the center of the hole. Let's say time dilation prevents them from ever coming together and going boom, the quarks will flatten out and smear onto the singularity at the core.

Essentially once you cross the event horizon all possible future outcomes end as 'stuff' smeared out on the 'surface' of the singularity at the core of the hole.

It's like the Wizard of Oz without plot holes... "Pay no attention to the man behind the curtain." The event horizon is a perfect curtain. If the hole is large enough the event horizon need not be a violent place at all. So it's entirely likely that the particles will behave as they should, but again, it just doesn't matter -- from the outside.

A wonderful theory and Stephen deserves every kudo and award for this work. However, I must disagree with one of the conclusions you've presented. If all of the stars have to go cold for this radiation to be detectable then it will never be detected because no detector will exist when all the stars go cold. The tree in the forest paradox.

I wonder what will happen when Hawking radiation from a formerly a multiple galaxy consuming black hole looses enough matter to no longer prevent light from escaping?

According to the theory, as the mass of the hole delines, the temperature of the Hawking radiation increases. Therefore all black holes will eventually evaporate in a blaze'o'glory.

The reason I say all the stars must go gold first, is because of the incredibly low temperature of the Hawking radiation for normal sized bodies. Boltzmann teaches us that radiation is exchanged between all bodies, the quantity of energy being proportional to the 4th power of the absolute temperature.
Far in the distant future, imagine a cold dead comet. The comet has a temperature equal to the cosmic background which over many billions of years has fallen to 0.001K As the comet drifts through space it approaches a black hole, that has sucked up all the other matter within several galactic diameters. It's dark in space, and it's cold. But we can calculate the energy being exchanges between these two bodies. Assume the Hawking radiation emanating from the hole has a color temperature of 0.000001K (1 millionth) But it would probably be lower, then the the ratio of the 4th powers of the temperatures tells us the comet is transferring 10¹² times more energy to the hole than it is receiving!

What that means is that as long as there is normal matter in the universe, the black holes are doing pretty much what we expect of black holes to do, they are sucking up everything in their surroundings, in a net sense. For every thousand tons of stuff that goes into the hole about a microgram comes out. I call that indetectable, in a real sense, calculable, but indetectable.

I understood your point quite clearly. You seem to have missed mine. When the universe is cold enough that Hawking radiation can be detected above the background noise of the universe it still will not be detected. If the temperature of the detector is at 1 millionth K then the detector will not function. If the temperature of the detector is warm enough for it to function then the universe will not be at 1 millionth K.

Three are no frozen angels dancing on the head of this pin. They are either frozen or dancing not both.

They are Shroedinger's angels. If you look they are dead, if not looking they can dance.

There is the added complication that electronic charge attraction forces can easily overcome gravity.

Would this mean that black holes could increase (if antimatter had a negative gravitational sign) mass by swallowing the normal matter of a spontaneous ether pair? I dunno, but in such a case, there should enormous quantities of antimatter near the event horizon of a black hole.

I guess not too long, we find out if Einstein or Hawking are correct or incorrect in this one detail (that changes a lot).

They are currently testing whether antihydrogen floats up or falls in gravity at CERN antimatter laboratory.

If antimatter fall up (or floats up in a vacuum), then there is a whole lot of Special Relativity to edit, at least parts of the section on gravity. If this were true then a large amount of matter would still make a gravity well in space-time alright, but to antimatter this would appear to be a symmetric hill.

I agree with what you write, that antimatter still has positive mass. However, even if objects were to have negative mass/energy they would still fall towards massive objects. There are two ways to look at this: the GR explanation is that the particle simply follows space-time curvature; the pseudo-classical physics explanation is that if they had negative mass the force would be directed away from the massic object, but the acceleration would be reversed by the sign of the mass (it's merely a special case of Galileo's discovery that objects fall at the same rate regardless of the value of their mass). On the other hand, objects with negative mass would repel both other similar objects and normal massive objects, thus falling outside Newton's third law.

The concept of objects that are accelerated away from heavy objects is mathematically possible: the requirement is that the mass is imaginary [in the sense of √(-1)]. The conceptual difficulty for such particles is that with three spatial dimensions the acceleration effect on other objects (including other imaginary objects) would appear to be undefined.

Apparent philosophical issues not too dissimilar (on the surface) to those above have in the past been satisfied by more refined (views of) physical laws, so I'm not going to say that such particles are impossible, merely that they do not seem to fit with my partial understanding of current physical theories

BTW, I would not wish to encode anything desirable in Gates.

No. F = G m1 m2 r², where positive force is in the attractive sense.

If m1 were imaginary, then the observer would find not attractive or repulsive force, but imaginary component of force, and to my knowledge no one has ever detected that or repulsive gravitation to this point.

If m1 < 0 (in other words the mass has a negative quantum associated with it that has heretofore not been explicit in the gravity equation, then F <0 (repulsive). This leads to a problem with Einstein's energy equation, E=mc². As written, this equation related the interchangeability and equivalence of matter and energy. As written, this has for all m<0, E<0 also, which we consider to be physically impossible, and inconsistent with what we know thus far about antimatter.

There must be an edit to Einstein's equation (if antimatter is repelled by normal matter), thus

E= |m|c² , or E= (√m²)c²

there is not imaginary component (that we know of yet), there is not even negative mass quantum number we know of (yet).

Yes, made a mistake here with the imaginary masses, but not as you postulate:

a = f/m = G.m(large)/r².

So regarless of the value (positive, negative, imaginary) of the small mass the direction of movement would be unchanged.

On the other hand, particles with negative mass would repel all other material, including each other. So they could never agglomerate into large enough objects to create localised gravitational effects. Even if such particles were to exist, the only way we could observe their gravitational effect is by accelerated rate of expansion of the universe, or by very small unaccountable variations in gravitational field, or by otherwise unaccountable reductions in the values of large masses relative to expectations.

Your theoretical attack is equally unworthy as I already said that, so far as I knew, negative mass is not superficially consistent with any existing theories of mass/matter. But then (last time I went into it) neither is "dark matter". Yes, negative gravitational mass (and negative energy) is inconsistent with our habitual concept of energy always being positive, but to the best of my knowlede there's nothing in the basic maths of GR to prevent this, and (to my mind) it's philosophically less strange than most of the present cosmological theories.

Equally, I stated that I have no idea what would be the implications of imaginary or complex masses, and similarly no way to even conceive of a method of detection.

Given the current description of the universe, specifically 90% of the mass is unobserved at this time and that the universe is expanding at an accelerating rate, I wonder if the following is possible:

You've stated that negative mass repels all other mass whether it is negative or positive. If a volume of negative and positive particles and positive aggregates are mixed, wouldn't the negative masses, if in high enough concentration cause that volume of material to expand at an accelerating rate? I can see that system geometry might affect the percentage of negative matter required to generate sufficient repulsion to cause the whole system to expand, but in a uniformly distributed system it seems that a 50% content would work. If non-uniform, then a higher content might be required, or clumping of the positive mass material might be expected.

Any insight on whether the universe expansion acceleration rate is also increasing, constant or declining over time?

Sorry. I know that the expansion rate is accelerating, but I'm not sure about the next derivative. Most theories I have seen suggest that it is positive. Although this is consistent with observations, I believe that there are too many issues of interpretation to say that the observations give strong support (if indeed any)

I agree that it is very likely that anti-matter and matter do not gravitationally repel, However, as the Wikipedia article points out, this has never been conclusively observed. The article also identifies several respected theories why gravity should always attract. But repeatable observation will trump any theory.

Hi redfred

I was not postulating antimatter to have negative mass, for the following reasons:

Negative mass particles would move the right way under gravitational field, but the wrong way under electric field. This should be observable, and I do not believe that antimatter has this property.

In addition, negative mass in my somewhat simple-minded scheme represents negative energy, both as regards the effect of rest-mass and as regards kinetic energy. So far as I know, the anihillation of matter and antimatter produces twice the energy represented by the mass of the matter, indicating either that the relation between mass and energy is broken, or that the antimatter has positive mass. Given the behaviour of zero-rest-mass photons, I personally consider positive mass the more likely explanation.

On the above basis, antimatter would be most likely gravitationally to attract matter.

This implies that negative-mass/energy matter would be something that we have not so far observed. Given that pre-existing negative-mass material is likely to be relatively uniformly distributed I would not expect to observe it unless we find a way to create it, and maybe interaction with normal matter would be so low that the only way we would know is if the particles we could observe had unaccountably high total energy.

How the heck does that work? Isn't the force in an electric field depending on the E field and the charge?

Sorry, I should have written magnetic field. I think that you are right that the electric felds under which these experiments are conducted are insufficient to make measurements on high-velocity particles. (Even then, the curvature would be quite small).

m small is negative, hence the acceleration is negative. How did you ever pass high school physics?Ω

If the force is negative being applied to a negative mass then the acceleration is positive.

There nothing wrong with a polite misunderstanding.

Often the one who insults first is the bigger fool.

OK, I was being a jerk. But if a is positive (the particle speeds up along its vector), if m is negative, so is f. Ok I agree to that.

We all do it sometimes, so apology accepted. (As I think I mentioned, my writings on this topic are personal speculations and purely theoretical, but not inconsistent with any theory known to me; but they would need a huge amount of filling out/in by my betters to become testable. I am unaware of any such detailed theory...)

I sometimes feel that even the following (attributed to Socrates) verges on arrogance: τούτου μὲν τοῦ ἀνθρώπου ἐγὼ σοφώτερός εἰμι· κινδυνεύει μὲν γὰρ ἡμῶν οὐδέτερος οὐδὲν καλὸν κἀγαθὸν εἰδέναι, ἀλλ᾽ οὗτος μὲν οἴεταί τι εἰδέναι οὐκ εἰδώς, ἐγὼ δέ, ὥσπερ οὖν οὐκ οἶδα, οὐδὲ οἴομαι· ἔοικα γοῦν τούτου γε σμικρῷ τινι αὐτῷ τούτῳ σοφώτερος εἶναι, ὅτι ἃ μὴ οἶδα οὐδὲ οἴομαι εἰδέναι.

I could not manage well the translation of Socrates Greek expression to common American English.

This is what Google Translate makes of it:

"Accordingly hand of man I am wiser; danger MEN gar our Neutral None kagathon eidenai good, but he hand oietai what eidenai qua eidos, I do not, osper CDV CDK one thing I know, neither oiomai; eoika fur Accordingly ce smikrῷ to a certain aftῷ toutῳ is wiser, that a nON one thing I know, neither oiomai eidenai."

WTF

Eschew obfuscation!

(WTF)¹⁷ That is why I said I could not obtain a coherent translation. Apparently, there are words in the Greek language for which there no English equivalent, or even an approximation.

Don't think that's true for modern Greek.

I stand corrected for the 17,000th time.

"The 'Ancient Greeks' didn't have the ancient greeks to study." -- Journal of Applied Psychology

Now it says energy....

The Unit electronvolt (or Mega Electronvolt) in this question refers to energy level of the particle, not its mass. Its not incorrect to state a mass as eV since E=mc². eV can, and is used interchangeably in particle physics.

^{https://en.wikipedia.org/wiki/Electronvolt}

Because by the time the neutrino had escaped from the sun and reached Earth its energy was not 14MeV.

Let's assume A) that such a neutrino exists and B) that such a detector might be possible.

Here are a few reasons why the detector may have failed to detect that neutrino:

1. The neutrino simply missed the detector. It travelled 'on a path' directly through the Earth, but for some reason the particle never reached the Earth. Perhaps the event occurred during a lunar eclipse and the neutrino was actually absorbed, or scattered, by the Moon.

2. The detector was simply not 'turned on' at the time. It may have been shut down for maintenance, or some type of failure caused it to be shut down.

3. 'Most' detectors work statistically. They examine thousands, millions, or billions of interactions and use statistics to draw conclusions about sub-atomic particles. The detection of a single particle is not statistically significant, so the 'detection' may have been placed in the 'interesting but not conclusive' file since there weren't enough detections of similar neutrinos to reach the '5-sigma' level.

Neutrinos oscillate between the three kinds: electron neutrino, muon neutrino, an tau neutrino.

https://en.wikipedia.org/wiki/Neutrino_oscillation

Wouldn't the 'capable of detecting every neutrino of that energy' qualifier rule out this answer? Even if the neutrino were to oscillate between different states or types, the energy would not change and it would remain a neutrino, right?

Well from what I've read it seems the neutrino oscillates between three states, each having different mass...at times returning to original state...so depending on where, in relation to source, you took a measurement, you may get any one of the possible measurements...

"Neutrino oscillation arises from a mixture between the flavor and mass eigenstates of neutrinos. That is, the three neutrino states that interact with the charged leptons in weak interactions are each a different superposition of the three neutrino states of definite mass. Neutrinos are created in weak processes in their flavor eigenstates^{[nb 1]}. As a neutrino propagates through space, the quantum mechanical phases of the three mass states advance at slightly different rates due to the slight differences in the neutrino masses. This results in a changing mixture of mass states as the neutrino travels, but a different mixture of mass states corresponds to a different mixture of flavor states. So a neutrino born as, say, an electron neutrino will be some mixture of electron, mu, and tau neutrino after traveling some distance."...

https://en.wikipedia.org/wiki/Neutrino_oscillation#Beam_neutrino_oscillation

In other words, neutrinos are very shifty characters...

Obviously there is some information not given, as usual for these puzzles. I am assuming that the "hypothetical perfect neutrino detector" detects 100 percent of the type of neutrino which was emitted by the sun (an electron neutrino) and not the other two types which it can morph into.

There's a trick somewhere. I'm just betting on neutrino oscillation.

https://en.wikipedia.org/wiki/Neutrino_oscillation

I am surprised that your correct answer has no GA. You should get 10!!!

I strongly disagree, because (as reiterated in JohnDG's response #163) this "solution" is clearly incompatible with the wording of the challenge question as posed (shame on the currently anonymous poser of the question). Moreover, there are at least two genuinely correct answers, although one (the better one in my opinion) depends on your interpretation of the question. (BTW, if we rewrite the challenge so that the poser's answer is both acceptable and optimum, somewhat over1/3 of originating neutrinos would still be detected)

The first and incontrovertibly correct answer to the challenge is that the specific neutrino is one of the minutely small proportion of neutrinos that loses substantial energy in collision with a neucleus but still continues on its original path that takes it through the Earth. From my point if view it is unsatisfactory in the sense that such particles will be incredibly rare, and that it is is a trivialisation of the physics - as any particle that passes through matter will be subject to rare events.

Therefore, my preferred answer is that the neutrino is one of the vast majority of those neutrinos that initially travel on a path that would take them through the Earth but that are diverted by virtue of the same interaction with the sun that accelerates their change of flavour. I appreciate that the challenge question is sufficiently ambiguous that this answer does not fit every interpretation of the challenge. The reason I personally prefer this answer in spite this is both that it would apply to the vast majority of the referenced neutrinos, and also that you won't readily find direct reference elsewhwere on the web to this effect, in which sense the answer requires some thought rather than a simple look-up. (N.B that this diversion does not reduce the total number of neutrinos that pass through the Earth, as there will on average be an equal number that start on paths that would miss the Earth but are diverted to pass through it)

The OP states that the neutrino passes through the Earth. Ergo any prior change to the particle created in the sun has already been effected. The OP says the answer is that the detector is tuned to a different flavor of neutrino ( i accept that this is my understanding of the OP's answer ) and as such i see this answer as worthy of a GA.

I find your view incomprehensible. How can you say that "all neutrinos" means the same as "the subset of neutrinos with a specific flavour"? This is simply not a case of missing information as Rixter appears to imply; it is a case of the answer simply not applying to the question that was posed. It is no different in principle from asking "How old am I" and then insisting that the (younger) age when you got were baptised/barmitsfahd/married or whatever is he "correct" answer.

Also, the OP does not state that explicitly that the neutrino passes through the Earth. It says specifically that it "travels on a path (that passes) directly through the Earth" (I have added the two words in braces to emphase the element of ambiguity). If the OP did not wish to leave this ambiguity he could easily have written that the "neutrino .... travels directly through the Earth", which is both less wordy and incontrovertible in meaning. This is why I feel justified in exploiting the ambiguity to recommend an answer that you will not readily find simply by searching the web, but that actually applies to the vast majority of neutrinos that initially travel on a path that would bring them through the Earth.

Of course the ambigouous wording allows answers a number of other answers which were already given:
That the path passes through the Earth at the moment the neutrino is released, but the Earth has moved out of the way by the time the neutrino arrives at the Earth's orbit.
That the detector is capable of detecting all neutrinos, but doen't necessarily do so unless activated (so "turned off").
These are both correct answers within the wording of the question, albeit you may not find them interesting.
The answer that the neutrino has lost enough energy not to be detected is correct under all possible interpretations of the challenge question, even though it is an extraordinarily unusual event when applied to the challenge as posed (but still not very interesting as such in my view, thought he rerety of such an event is slightly mor interesting).
The comment that the neutrino changes flavour and would not therefore be detected by neutrino detectors that were designed to detect it as originally emitted is interesting, is of practical importance and has resulted in some interesting physics. Unfortunately it is impossible to find any ambiguity in the challenge as posed that would allow this as an answer.

If we disallow all ambiguities (jump on me if I've still missed some), the question might read as follows:
"A neutrino with an energy of 14 MeV is released from a reaction in the core of the sun and travels directly through Earth. An ideal neutrino detector that detects every neutrino of that energy passing through Earth fails to detect it. Why?"
That question clearly has only one possible answer: that the neutrino no longer has that energy. The neutrino could in principle have gained energy due to coinciding with a complex neuclear event, but the other correct aswer (and the less unlikely event) is that the neutrino has collided with a nucleon and lost sufficient energy that it is not detected. Note that the new wording does not imply that the neutrino started out in a path that would have taken it through the Earth, so the probability of this event is actually quite reasonable.

You would have to work quite hard to set a challenge question that allowed the flavour answer without almost giving the game away to those who have followed the faster-than-light issue. The best I have come up with is:
"A neutrino with an energy of 14 MeV is released from a reaction in the core of the sun and travels directly through Earth. An ideal neutrino detector that detects every neutrino that passes through Earth and that has the same characteristics fails to detect it. Why?"
What I don't like about this version of the question is that it this relies on exploiting a semantic ambiguity in order to allow the desired answer without giving the game away.
Can anyone do better?

Your first sentence explains the difficulty you have. Sorry, can't copy and paste in this browser. You said, in part, "all neutrinos" which is your understanding of the OP's statement "every neutrino of this energy". I see the qualifier as being important. Interestingly, you have also seen the importance of this qualifier as you have proffered alternative wording to exclude ambiguity to allow the OP's answer to work. New para ( also no formatting in this browser ). I want to thank you for the education. This forum is a fun way to learn and your knowledge and your willingness to share is appreciated. I would love to sit on the verandah with a few bevy's and chew the fat with you. But i fear it may be all one way and you would end up drained. :-( Jim

Someone else already made the point specifically that "every neutrino of this energy" would include all flavours of neutrino with this energy, and I think both that person and I explained that the total energy of a neutrino does not change at all simply because it changes flavour.

Again, as breifly discussed elsewhere, had the OP talked in terms of kinetic energy rather than just energy this would indeed have represented a change as the neutrino changes flavour; however the maximum possible change would be 0.04eV*. or less than 3 parts per billion. This would rather be pushing things as an explanation why the detector failed to detect the paerticle when it detected absolutel every neutrino at 40meV difference.

*This is an upper bound based on flavour oscillations alone, other evidence suggests that the rest-mass difference is somewhat smaller than this, but the actual value is unknown.

I've already taken up more than my fair share of this thread, so I'll try and restrain myself...

OK, I like your answer. It's the best answer so far.

Thanks

I thought neutrinos accounted for windage.

No need. The solar wind is at its back.

Actually, I'm not entirely sure that even the idea of following a path toward the Earth is valid, according to quantum physics. It should take all paths, or no paths, until the detector detects it, and then it will "realize" which path it "took," post facto.

It doesn't say it's aimed at the Earth, it says it travels on a path through the Earth...I have to go with oscillation...

You could be right. I'm trying to think of how I would phrase that part of the question if I had my answer in mind, and I'm not sure I would use these words.

That is not exactly how the problem was stated. I think it has more to do with gravity wells...and if it was trajectory, it could eons for that neutrino just born at sol's core to arrive at sol surface (takes photons a hell of a long time to get out of the sun). Not only that, processes in the mid and upper layers of the sun probably have a pretty good cross-section for capture of this neutrino, just guessing, but there is something about protons capturing electrons and needing a neutrino to finish the conversion to a neutron, I think (sort of the reverse reaction to free neutron decay).

I know that photons don't have identity, but the reason that light takes so long is that the original photons are absorbed and new thermal photons are emitted - myriads of times. When (rarely) a neutron interacts with matter the reduced energy (and slightly redirected) neutron appears almost instantaneously. The probability of a significant delay is minimal.

How was neutrino absorption cross section under conditions extant in the sun measured? Assumed? You gotta be kidding me! You say neutrons, everyone else is talking neutrinos... are we on the same page here?

Apologies for the typos. Of course I meant neutrinos. (I don't normally have much to do with neutrino work, and I've been dealing with neutron effects recently, so typing that is automatic once I get to as far as the t - unless I really, really concentrate on the typing). It's too late to correct now, unfortunately.

The cross sections are mainly calculated from models of the effects (the models being checked via among other things known generation levels), but the calculations are confirmed by Earthly* experiments such as OPERA, in which muon neutrinos were generated and the beam observed to contain no tau-neutrinos locally to the generation, and then after 730-km a few tau-neutrinos were detected. The resolution of the confirmatory data is currently very poor (only 5 tau-neutrinos as of June 2015), but good enough for order-of-magnitude statements (which are more than good enough for present purposes).

*Nuclei in the sun are no different from those on Earth, though they will be moving rather faster (up to about c/500) - but the neutrino's Velocity is very near the speed of light, so the movement of the nuclei is almost irrelevant so far as the interaction is concerned.

Neutrino detectors are large, but, not that large. It's easy for a neutrino to pass right through the centre of the earth, but miss a detector by several thousand miles.

See my proposed solution #11. I think the Earth-sized detector was a science-fictiony kind of thing that just sets up the problem, and the way it is set up makes me think that all the info about neutrinos is just misdirection. It really has to do with the width of the Earth and the path of the neutrino. In fact, just mentioning neutrinos at all is already misdirection, because the same thing will happen with any photon leaving the sun directly toward the Earth.

Awww just missed....

A neutrino walks into a bar...

and goes right on through.

Then the bartender says, "We don't allow your kind in here!"

A tachyon walks into a bar...

Well there seems to be a lot of conflicting information on neutrinos...They travel at the speed of light, but anything with mass supposedly can't travel at the speed of light...then some say neutrinos travel faster than light, which would seem to be impossible altogether....then we have the oscillation where neutrinos change into different combinations of state...then we have some conflict over what energy means when referring to a neutrino....I wonder if Jorrie could shed some light here? Oh Jorrie come in please....

"They travel at the speed of light"
Not any more: but Pauli's initial theory (1930) had them massless. Fermi (1934) was dubious about this, however.

"Some say neutrinos travel faster than light"
OPERA found their batches of neutrinos were arriving earlier than the timing link indicated they should - i.e apparently travelling faster than light. The experimentalists who made the observations and most of the scientific community were sceptical, delaying judgement until the experiment could be repeated elsewhere. Even before any contradictory information could be found, the experimentalists found the source of the problem - an unidentified poor fibre-optic connection in the timing link.
I remember (perhaps unreliably) that timing checks were also attempted against GPS, but various difficulties associated with variable direction ov the vertical caused by working underground in a massively mountanous region made these checks of dubious validity.
BTW, the speed of these high-energy neutrinos is currently indistinguishable form that of light to within the limits of the experiment (now the most precise available - albeit this was never the original objective of the work).

"Oscillations"
Yes. There is experimental evidence for oscillations - also from OPERA (its original mission). A muon-neutrino beam originating in CERN was found to contain tau-neutrions when it arrived in LN Gran Sasso.

Neutrons and the Standard Model
The Standard Model has been very successful, but the number of solar electron-neutrinos detected was around half of expectations (the ratio depended the energy of the neutrino). The postulated explanation for this was that neutrinos could oscillate between the different types (though in my ignorance I don't know whether the term "oscillate" is meant to suggest a constant rate); but this is only possible if the neutrons have mass. The observation of oscillation by OPERA and confirmation (with additional detail) by the Daya Bay experiments.
There were also cosmological reasons to abelieve that neutrinos have rest-mass, and the average mass of a neutrino is thought to be about 0.1eV.

Sorry I'm not Jorrie, but I hope this is helpful anyway

Fyz

According to the literature, it takes a supernova to generate a 14MeV neutrino.

In the event that a 14MeV neutrino from the sun passes through earth, missing the measurement would be the least of our problems.

Maybe that's the answer. The detector is vaporized before it can detect the neutrino.

Link please....

Maybe it only takes a supernova to allow the high energy neutrino to escape?

0.1% of neutrinos generates in the solar core are 8Boron decay neutrinos with an initial energy of about 15MeV

https://www2.warwick.ac.uk/fac/sci/physics/staff/academic/boyd/stuff/lec_neutrinodetectors_writeup.pdf

But the challenge states the neutrino was produced by a fusion process. The 15 MeV neutrino production reaction is a Beta decay reaction that converts one atom into two atoms, not a fusion reaction.

The challenge also originally stated the neutrino had a mass and not energy of 15 MeV. Thus almost anything could be deemed as the official answer.

Ha-Ha! But since the Neutrino would pass through the star's shell at nearly the speed of light while the shockwave *MUST* travel much s*l*o*w*e*r, the Neutrino would arrive at Earth with time to spare for the detection -- but probably not time to publish!