7 ms·

How physicists track and trap the elusive neutrino

69 points by ibobev 4mo ago

ktallett 4mo ago
There is a good exhibit on this at the Miraikan in Odaiba, Tokyo. Detecting things and proving we detected what we detected we previously couldn't is always a fascinating exercise, especially whilst so much matter is still unrecognised.
SiempreViernes 4mo ago
For anyone wondering about the title, by "trap" they mean "detect destructively": there are no stable neutrinos in a bottle in this article.
- Varelion 4mo ago
  Damn it. Heart rate sky-rocketed from excitement.
- stouset 4mo ago
  That would be a wild thing to accomplish, given that neutrinos are created at relativistic speeds, have virtually zero mass, and don’t react with anything but gravity and the weak force. Whatever gravity “trap” you make is going to pale in comparison to the gravity wells around us (earth, the sun, etc) and the weak force scales exponentially with energy. So a slow-moving neutrino would interact even less with the weak force than a relativistic one.
  - amelius 4mo ago
    What if you make the trap move at relativistic speed?
    - stouset 4mo ago
      Speed is relative, so if you accelerated away from the sun at 0.999999c hoping to hang out in a slow-moving stream of solar neutrinos, you’d remove the energy needed for them to interact with the weak force. They’d be all around you, but you would have exponentially smaller chances of interacting with them.
  - __MatrixMan__ 4mo ago
    Are there a bunch of slow neutrinos sloshing around near the center of the earth?
    - stouset 4mo ago
      Probably! And even potentially some orbiting the planet. They’d be part of the cosmic neutrino background, neutrinos around since the big bang which have had their velocity red-shifted to Newtonian speeds. But they interact with things even less than relativistic neutrinos. Even a light-year of lead wouldn’t be enough to register a hit from one.
      - sigmoid10 4mo ago
        And even if you did have light-years of super dense detector material lying around, the energy deposited by such a neutrino is so tiny that you wouldn't be able to register the hit.
  - SiempreViernes 4mo ago
    Indeed, which is why its so annoying the editor chose to put "trap" in the title!
semiquaver 4mo ago
HN automangled the title, should have a “how” at the beginning. The change makes the headline sound like this is news, but it’s just a description of neutrino detectors.
- dang 4mo ago
  Rehowed now. Thanks!
  - dredmorbius 4mo ago
    Now howed, brown cow?
mrguyorama 4mo ago
Wonderful pictures! The Super Kamiokande had a terrible engineering event where the delicate sensor bulbs shattered, and the pressure delta from one shattering caused neighbors to shatter, in a chain reaction that destroyed large amounts of sensors. https://www.youtube.com/watch?v=YoBFjD5tn_E https://www.youtube.com/watch?v=YoBFjD5tn_E Unrelated: >Neutrinos come in three different “flavors” (electron, muon, and tau) and can oscillate, or switch, between them. To do so, neutrinos must have mass Why? What actually is "Neutrino oscillation" and why does it require the neutrino have mass? My already feeble understanding of particle and quantum physics always breaks down at these sorts of points. How are we sure that the neutrino is in fact a single particle that should use the same sort of mathematical machinery as all others? Am I even asking a question that means something? I know literally every physicist ever graduated has spent time thinking everything in physics is wrong and tried poking at such ideas, so I guess I'm more interested in what those kids end up finding that brings them back to "No this makes more sense" of neutrinos in the standard model.
- puzzledobserver 4mo ago
  Disclaimer: I'm not a physicist. For a particle to "oscillate", it must "experience" time. All massless particles travel at the speed of light. As a consequence of special relativity, they don't "experience" time. Therefore, neutrinos must be traveling slower than light, and they must have mass.
  - mrguyorama 4mo ago
    Oh, duh. I can follow that logic now. The meat of my question is much dumber though: How do we know the "Same" neutrino is oscillating? We don't even have concrete understanding of how they would have mass, and different existing concepts of how it could be are problematic. There's so much the standard model isn't sufficient for, in terms of explanations and predictions and categorization, that it always feels odd to me when we shove another weird thing into the "Particle" bucket. It's also a dumb complaint though. A lot of deficiencies probably come down to simply not having enough good data to distinguish different ideas. It's hard to get good data with something that "Barely interacts" with anything else, by definition. Also maybe my complaint is entirely semantic, that a naturally unfinished or incomplete theory is presented as "We know". If you model a scientific theory developing over time, are we still so early that neutrino oscillation could actually be entirely different? Or do we actually have the data to demonstrate that "No, a singular neutrino absolutely changes to different flavors over time, nothing else could cause the effects we see in X, Y and Z demonstrations"? Like, I have sky high confidence that the standard model captures and predicts things like electrons and protons and quarks extremely well, so it always feels dissonant when we see things get weird like this, but also nature doesn't promise us coherent rules, just consistent ones. Reality could very well be full of crummy edge cases. Just sucks that I'll be dead before we really figure most of this stuff out. Also WTF even is time.... Why does something that is in one state, sometimes, be in a different state.... Is it even real? You can travel through space because you can have a spacial velocity, and that velocity can change through forces acted upon you, but is it even possible for there to be an analogous set of forces that can change your "Time velocity".... I'll have to buy my physicist friend a drink so I can have him laugh at me for weird, half baked philosophy questions that aren't really valid.
gattr 4mo ago
Could a physicist comment on this? I've been reading on the CNO cycle [1], where it says neutrinos produced in the beta-decay steps can have any share of the resulting energy. Does it mean the Sun is shrouded in a rarefied cloud of such low-energy neutrinos which failed to achieve escape velocity? [1] https://en.wikipedia.org/wiki/CNO_cycle https://en.wikipedia.org/wiki/CNO_cycle
- adrian_b 4mo ago
  This is an interesting question, but it would be very difficult to verify. Only neutrinos with an extremely low kinetic energy would have velocities much lower than that of light, and the fraction of such neutrinos from the total flux of neutrinos would be very small. If they did not escape Sun, most would be probably captured sooner or later by nuclei from the gases of the Solar atmosphere (i.e. chromosphere or corona).
anonymousiam 4mo ago
From the (captions under photographs) in the article: 'Located 2.1 kilometers underground in the Creighton mine in Ontario, Canada, the Sudbury Neutrino Observatory’s detector (left) was filled with “heavy” water, which features deuterium in place of hydrogen atoms. Its findings provided evidence that neutrinos can change, or “oscillate,” between different flavors.' "China’s Jiangmen Underground Neutrino Observatory (JUNO), seen here under construction in 2023, is currently the world’s largest neutrino detector. It began collecting data in August 2025; one of its main goals is to determine the outstanding mystery of how heavy each flavor of neutrino is." The second caption implies that some "flavors" of neutrino may be heavier than other flavors. The first caption says that neutrinos oscillate between different flavors. If the first caption is correct, then wouldn't each flavor of neutrino be just as heavy as the others?
- cobbzilla 4mo ago
  I also wonder this! Some real physicist tell me what I’m getting wrong here: neutrinos have mass but the magnitude is so infinitesimally small, and the oscillation smaller still, such that you’re bumping up against some fundamental properties of the universe and the oscillation is “borrowing” and “returning” some tiny amount of mass/energy from the vacuum.
  - deleted 4mo ago
    [deleted]
  - falseprofit 4mo ago
    Not a physicist, but here are a couple Wikipedia excerpts I found: From page “Conservation of mass”: “In general, mass is not conserved. The conservation of mass is a law that holds only in the classical limit.” From page “Neutrino oscillation”: “Neutrino oscillation arises from mixing 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 (propagating) neutrino states of definite mass. Neutrinos are produced and detected in weak interactions as flavour eigenstates[a] but propagate as coherent superpositions of mass eigenstates.[23]”
IndySun 4mo ago
Related BBC radio 4. Featuring the lovely Frank Close (I added the lovely). https://www.bbc.co.uk/programmes/b0106tjc https://www.bbc.co.uk/programmes/b0106tjc

69 points by ibobev 4mo ago

There is a good exhibit on this at the Miraikan in Odaiba, Tokyo. Detecting things and proving we detected what we detected we previously couldn't is always a fascinating exercise, especially whilst so much matter is still unrecognised.

SiempreViernes 4mo ago

For anyone wondering about the title, by "trap" they mean "detect destructively": there are no stable neutrinos in a bottle in this article.

Varelion 4mo ago
Damn it. Heart rate sky-rocketed from excitement.
stouset 4mo ago
That would be a wild thing to accomplish, given that neutrinos are created at relativistic speeds, have virtually zero mass, and don’t react with anything but gravity and the weak force. Whatever gravity “trap” you make is going to pale in comparison to the gravity wells around us (earth, the sun, etc) and the weak force scales exponentially with energy. So a slow-moving neutrino would interact even less with the weak force than a relativistic one.
- amelius 4mo ago
  What if you make the trap move at relativistic speed?
  - stouset 4mo ago
    Speed is relative, so if you accelerated away from the sun at 0.999999c hoping to hang out in a slow-moving stream of solar neutrinos, you’d remove the energy needed for them to interact with the weak force. They’d be all around you, but you would have exponentially smaller chances of interacting with them.
- __MatrixMan__ 4mo ago
  Are there a bunch of slow neutrinos sloshing around near the center of the earth?
  - stouset 4mo ago
    Probably! And even potentially some orbiting the planet. They’d be part of the cosmic neutrino background, neutrinos around since the big bang which have had their velocity red-shifted to Newtonian speeds. But they interact with things even less than relativistic neutrinos. Even a light-year of lead wouldn’t be enough to register a hit from one.
    - sigmoid10 4mo ago
      And even if you did have light-years of super dense detector material lying around, the energy deposited by such a neutrino is so tiny that you wouldn't be able to register the hit.
- SiempreViernes 4mo ago
  Indeed, which is why its so annoying the editor chose to put "trap" in the title!

semiquaver 4mo ago

HN automangled the title, should have a “how” at the beginning. The change makes the headline sound like this is news, but it’s just a description of neutrino detectors.

dang 4mo ago
Rehowed now. Thanks!
- dredmorbius 4mo ago
  Now howed, brown cow?

mrguyorama 4mo ago

Wonderful pictures! The Super Kamiokande had a terrible engineering event where the delicate sensor bulbs shattered, and the pressure delta from one shattering caused neighbors to shatter, in a chain reaction that destroyed large amounts of sensors. https://www.youtube.com/watch?v=YoBFjD5tn_E https://www.youtube.com/watch?v=YoBFjD5tn_E Unrelated: >Neutrinos come in three different “flavors” (electron, muon, and tau) and can oscillate, or switch, between them. To do so, neutrinos must have mass Why? What actually is "Neutrino oscillation" and why does it require the neutrino have mass? My already feeble understanding of particle and quantum physics always breaks down at these sorts of points. How are we sure that the neutrino is in fact a single particle that should use the same sort of mathematical machinery as all others? Am I even asking a question that means something? I know literally every physicist ever graduated has spent time thinking everything in physics is wrong and tried poking at such ideas, so I guess I'm more interested in what those kids end up finding that brings them back to "No this makes more sense" of neutrinos in the standard model.

puzzledobserver 4mo ago
Disclaimer: I'm not a physicist. For a particle to "oscillate", it must "experience" time. All massless particles travel at the speed of light. As a consequence of special relativity, they don't "experience" time. Therefore, neutrinos must be traveling slower than light, and they must have mass.
- mrguyorama 4mo ago
  Oh, duh. I can follow that logic now. The meat of my question is much dumber though: How do we know the "Same" neutrino is oscillating? We don't even have concrete understanding of how they would have mass, and different existing concepts of how it could be are problematic. There's so much the standard model isn't sufficient for, in terms of explanations and predictions and categorization, that it always feels odd to me when we shove another weird thing into the "Particle" bucket. It's also a dumb complaint though. A lot of deficiencies probably come down to simply not having enough good data to distinguish different ideas. It's hard to get good data with something that "Barely interacts" with anything else, by definition. Also maybe my complaint is entirely semantic, that a naturally unfinished or incomplete theory is presented as "We know". If you model a scientific theory developing over time, are we still so early that neutrino oscillation could actually be entirely different? Or do we actually have the data to demonstrate that "No, a singular neutrino absolutely changes to different flavors over time, nothing else could cause the effects we see in X, Y and Z demonstrations"? Like, I have sky high confidence that the standard model captures and predicts things like electrons and protons and quarks extremely well, so it always feels dissonant when we see things get weird like this, but also nature doesn't promise us coherent rules, just consistent ones. Reality could very well be full of crummy edge cases. Just sucks that I'll be dead before we really figure most of this stuff out. Also WTF even is time.... Why does something that is in one state, sometimes, be in a different state.... Is it even real? You can travel through space because you can have a spacial velocity, and that velocity can change through forces acted upon you, but is it even possible for there to be an analogous set of forces that can change your "Time velocity".... I'll have to buy my physicist friend a drink so I can have him laugh at me for weird, half baked philosophy questions that aren't really valid.

gattr 4mo ago

Could a physicist comment on this? I've been reading on the CNO cycle [1], where it says neutrinos produced in the beta-decay steps can have any share of the resulting energy. Does it mean the Sun is shrouded in a rarefied cloud of such low-energy neutrinos which failed to achieve escape velocity? [1] https://en.wikipedia.org/wiki/CNO_cycle https://en.wikipedia.org/wiki/CNO_cycle

adrian_b 4mo ago
This is an interesting question, but it would be very difficult to verify. Only neutrinos with an extremely low kinetic energy would have velocities much lower than that of light, and the fraction of such neutrinos from the total flux of neutrinos would be very small. If they did not escape Sun, most would be probably captured sooner or later by nuclei from the gases of the Solar atmosphere (i.e. chromosphere or corona).

anonymousiam 4mo ago

From the (captions under photographs) in the article: 'Located 2.1 kilometers underground in the Creighton mine in Ontario, Canada, the Sudbury Neutrino Observatory’s detector (left) was filled with “heavy” water, which features deuterium in place of hydrogen atoms. Its findings provided evidence that neutrinos can change, or “oscillate,” between different flavors.' "China’s Jiangmen Underground Neutrino Observatory (JUNO), seen here under construction in 2023, is currently the world’s largest neutrino detector. It began collecting data in August 2025; one of its main goals is to determine the outstanding mystery of how heavy each flavor of neutrino is." The second caption implies that some "flavors" of neutrino may be heavier than other flavors. The first caption says that neutrinos oscillate between different flavors. If the first caption is correct, then wouldn't each flavor of neutrino be just as heavy as the others?

cobbzilla 4mo ago
I also wonder this! Some real physicist tell me what I’m getting wrong here: neutrinos have mass but the magnitude is so infinitesimally small, and the oscillation smaller still, such that you’re bumping up against some fundamental properties of the universe and the oscillation is “borrowing” and “returning” some tiny amount of mass/energy from the vacuum.
- deleted 4mo ago
  [deleted]
- falseprofit 4mo ago
  Not a physicist, but here are a couple Wikipedia excerpts I found: From page “Conservation of mass”: “In general, mass is not conserved. The conservation of mass is a law that holds only in the classical limit.” From page “Neutrino oscillation”: “Neutrino oscillation arises from mixing 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 (propagating) neutrino states of definite mass. Neutrinos are produced and detected in weak interactions as flavour eigenstates[a] but propagate as coherent superpositions of mass eigenstates.[23]”

IndySun 4mo ago

Related BBC radio 4. Featuring the lovely Frank Close (I added the lovely). https://www.bbc.co.uk/programmes/b0106tjc https://www.bbc.co.uk/programmes/b0106tjc