Elusive neutrino
If you think that a vacuum is a real void, then you are greatly mistaken. Even the cold interstellar space, not to mention the artificially created vacuum, is not so empty. On average, one proton and one electron per cubic meter of the Universe. Even in the same cubic there are on average 500 million relic photons and as many relic neutrinos. Our Universe is not only glowing from the inside, from the first millisecond of the Big Bang, but is also “neutrinated” as intensely.
Intrigued? Did you know that:
Theoretically predicted, a particle could be observed only by indirect methods. If now such an approach practically does not raise doubts among physicists, then more than half a century ago the evidence was considered ephemeral and doubtful. What is the salt of the problem? The fact that neutrinos are extremely difficult to catch directly. The classic experiment to find the neutrino is the reverse beta decay:
')
antineutrino + proton -> positron + neutron + photons
In the future, the neutron was captured by the substance of the detector with the release of photons. That is, two flashes of light, the next with intervals - this is a sign of antineutrino. Would you believe?
Neutrino detectors are located in the thickness of the substance - in the mountains, in the ice of Antarctica, in the mines - precisely to eliminate any side channels of the formation of “flares”, except for the all-penetrating neutrino channel. The water detector is a convenient container for capturing neutrons. Simplistically, a neutrino detector is a giant ice cube (scintillator) in which spokes from photon detectors are inserted, recording the smallest emission of radiation.
Two flashes - that's neutrinos. It is hard to believe, but there were a lot of such experiments, statistics were gathered. And most importantly, neutrinos became only the first sign in the new model of theoretical physics, when the theory was ahead of the experiment, and predicted the existence of particles and effects long before they were experimentally confirmed. The neutrino was theoretically invented, “fitted” in properties to explain the discrepancies in the experiment, and only then indirectly discovered. Neutrinos cannot be touched and measured with a common yardstick, it is so special, and it remains only to believe :)
The physical uniqueness of the neutrino is in the absence of electrical charge (does not participate in electromagnetic interactions) and “color” (not subject to quantum chromodynamics). The remaining "weak" and gravitational interactions, respectively, are a million and 10 ^ 38 degrees less intense than the "strong" ones. As a result, the neutrino travels through the Universe, penetrating matter and time, having extremely low chances of being noticed and “caught” by another particle. Also, other leptons (electron, muon and taon) that are not subject to chromodynamics have an electric charge, and are not suitable for the role of perpetual travelers in space.
By the way, about the uniqueness of the neutrino disputes are no less stormy. If it is really neutral in all senses, what is anti- neutrino? And what is their difference? After all, if an electron has a negative electric charge that we are used to (it’s also a convention in itself, by the way, we could call an electron a positron, and vice versa), then the neutrino doesn’t have any charges. You can absolutely say that the choice of particles and antiparticles in this case was completely arbitrary, terminological. The differences between the neutrino and the antineutrino had to be explained by the Nobel laureate Landau and his theory of deep CP symmetry (charge-parity symmetry). True, in 1964, the CP symmetry violation in the decay of a neutral kaon was safely proved, which led to the prediction of the third generation of quarks, but this is a separate story. It is believed that a series of experiments found no reactions that contradict the fundamental difference between neutrinos and antineutrinos, that is, they can be considered different.
The search for differences in neutrinos from antineutrinos and the so-called lepton charge led to a theoretical assumption, which was experimentally proved in 1962 - neutrinos are not as neutral as they were supposed to be. It has a lepton charge, and all leptons are divided into families (three in the modern Standard Model, and at that time the first two were known), and the neutrino is electron, muonic, and taonic. The physical implications of this discovery are extremely interesting - since the particle families make it possible to build theories of the Great Union and the evolution of matter, but for our simple excursus we note that neutrinos are not one particle, but as many as three (plus three of their anti pods).
What else is interesting neutrino? For example, neutrino physics does not require an investment of trillions of dollars and the construction of the Large Hadron Collider. In the fifth year, we went to Protvino every week for the U-70 proton synchrotron, which is still used regularly for scientific experiments. The Labeled Neutrino complex, an advanced breakthrough of physical thought in those years, and now has not lost its relevance.
But besides accelerators and the relic background, there are still powerful sources of neutrinos - stars. Observation of neutrinos emitted by stars proved the thermonuclear nature of stars - which, generally speaking, is not obvious - there are many types of stars, and our sun is not the most representative and interesting among them. And neutrino astronomy is a real science. First, neutrinos form in stars (remember the teaser at the beginning? Neutrinos are an essential component of a thermonuclear reaction), and secondly they pierce other stars through and reach the Earth. Which, theoretically, can give us information from the most stellar depths. Neutrino telescopes are actually located deep in the Earth’s thickness, and they detect the flow of particles passing through the Earth’s thickness from its reverse side! Such telescopes operate in many countries, including Russia - BAIKAL at a depth of 1 km in the waters of Baikal, and Baksan in the Caucasus.
From the realm of science fiction (but not abstract, but limited only by the sensitivity of the instruments), it is neutrino astronomy that is able to prove the existence of antiworlds — galaxies, which consist entirely of antimatter. After all, “anti-stars” generate the same indistinguishable flow of standard photons, like ordinary stars. But the most powerful stream of neutrinos from them will all have the prefix " anti ". Also, the neutrino telescope can very well determine the collapse of a star (into a supernova, black hole or dwarf) within our Galaxy.
And for dessert: two more paradoxes and many theories are associated with neutrinos, which are currently not possible to confirm or deny. The neutrino flux from the sun has been consistently less theoretically calculated, for many decades now. The theory that tries to explain the shortage is the oscillation of the neutrino, the transformation of one type into another (electron to muon), the non-conservation of the lepton charge, respectively, the symmetry flying to the devil's grandmother and the triumph of the supporters of the Great Unification theories for which everyone is equal (but only at high energies) . But if neutrinos oscillate, then they have a non-zero (and different) mass. A non-zero neutrino mass will make life difficult for theoretical physicists, but astronomers will breathe freely - they do not have a debit with credit, the observed mass of the Universe is critically less than that required by the theory. And the “hidden” matter could then be honorably given to the power of the all-pervasive and elusive neutrinos that gained mass.
This concludes the popular science introduction to neutrino physics completed, if successful with the public, I can continue to recall my student years at the Physics Department :)
Intrigued? Did you know that:
- Neutrinos are an integral part of the thermonuclear reaction that gives life to stars.
- Antineutrinos carry about 2% of the energy of a nuclear reactor to the expanses of the Galaxy.
- The “neutron” familiar to us could symbolize the neutrino if the debate about the existence of a mysterious particle would not have lasted until the discovery of a real neutron.
Theoretically predicted, a particle could be observed only by indirect methods. If now such an approach practically does not raise doubts among physicists, then more than half a century ago the evidence was considered ephemeral and doubtful. What is the salt of the problem? The fact that neutrinos are extremely difficult to catch directly. The classic experiment to find the neutrino is the reverse beta decay:
')
antineutrino + proton -> positron + neutron + photons
In the future, the neutron was captured by the substance of the detector with the release of photons. That is, two flashes of light, the next with intervals - this is a sign of antineutrino. Would you believe?
Neutrino detectors are located in the thickness of the substance - in the mountains, in the ice of Antarctica, in the mines - precisely to eliminate any side channels of the formation of “flares”, except for the all-penetrating neutrino channel. The water detector is a convenient container for capturing neutrons. Simplistically, a neutrino detector is a giant ice cube (scintillator) in which spokes from photon detectors are inserted, recording the smallest emission of radiation.
Two flashes - that's neutrinos. It is hard to believe, but there were a lot of such experiments, statistics were gathered. And most importantly, neutrinos became only the first sign in the new model of theoretical physics, when the theory was ahead of the experiment, and predicted the existence of particles and effects long before they were experimentally confirmed. The neutrino was theoretically invented, “fitted” in properties to explain the discrepancies in the experiment, and only then indirectly discovered. Neutrinos cannot be touched and measured with a common yardstick, it is so special, and it remains only to believe :)
The physical uniqueness of the neutrino is in the absence of electrical charge (does not participate in electromagnetic interactions) and “color” (not subject to quantum chromodynamics). The remaining "weak" and gravitational interactions, respectively, are a million and 10 ^ 38 degrees less intense than the "strong" ones. As a result, the neutrino travels through the Universe, penetrating matter and time, having extremely low chances of being noticed and “caught” by another particle. Also, other leptons (electron, muon and taon) that are not subject to chromodynamics have an electric charge, and are not suitable for the role of perpetual travelers in space.
By the way, about the uniqueness of the neutrino disputes are no less stormy. If it is really neutral in all senses, what is anti- neutrino? And what is their difference? After all, if an electron has a negative electric charge that we are used to (it’s also a convention in itself, by the way, we could call an electron a positron, and vice versa), then the neutrino doesn’t have any charges. You can absolutely say that the choice of particles and antiparticles in this case was completely arbitrary, terminological. The differences between the neutrino and the antineutrino had to be explained by the Nobel laureate Landau and his theory of deep CP symmetry (charge-parity symmetry). True, in 1964, the CP symmetry violation in the decay of a neutral kaon was safely proved, which led to the prediction of the third generation of quarks, but this is a separate story. It is believed that a series of experiments found no reactions that contradict the fundamental difference between neutrinos and antineutrinos, that is, they can be considered different.
The search for differences in neutrinos from antineutrinos and the so-called lepton charge led to a theoretical assumption, which was experimentally proved in 1962 - neutrinos are not as neutral as they were supposed to be. It has a lepton charge, and all leptons are divided into families (three in the modern Standard Model, and at that time the first two were known), and the neutrino is electron, muonic, and taonic. The physical implications of this discovery are extremely interesting - since the particle families make it possible to build theories of the Great Union and the evolution of matter, but for our simple excursus we note that neutrinos are not one particle, but as many as three (plus three of their anti pods).
What else is interesting neutrino? For example, neutrino physics does not require an investment of trillions of dollars and the construction of the Large Hadron Collider. In the fifth year, we went to Protvino every week for the U-70 proton synchrotron, which is still used regularly for scientific experiments. The Labeled Neutrino complex, an advanced breakthrough of physical thought in those years, and now has not lost its relevance.
But besides accelerators and the relic background, there are still powerful sources of neutrinos - stars. Observation of neutrinos emitted by stars proved the thermonuclear nature of stars - which, generally speaking, is not obvious - there are many types of stars, and our sun is not the most representative and interesting among them. And neutrino astronomy is a real science. First, neutrinos form in stars (remember the teaser at the beginning? Neutrinos are an essential component of a thermonuclear reaction), and secondly they pierce other stars through and reach the Earth. Which, theoretically, can give us information from the most stellar depths. Neutrino telescopes are actually located deep in the Earth’s thickness, and they detect the flow of particles passing through the Earth’s thickness from its reverse side! Such telescopes operate in many countries, including Russia - BAIKAL at a depth of 1 km in the waters of Baikal, and Baksan in the Caucasus.
From the realm of science fiction (but not abstract, but limited only by the sensitivity of the instruments), it is neutrino astronomy that is able to prove the existence of antiworlds — galaxies, which consist entirely of antimatter. After all, “anti-stars” generate the same indistinguishable flow of standard photons, like ordinary stars. But the most powerful stream of neutrinos from them will all have the prefix " anti ". Also, the neutrino telescope can very well determine the collapse of a star (into a supernova, black hole or dwarf) within our Galaxy.
And for dessert: two more paradoxes and many theories are associated with neutrinos, which are currently not possible to confirm or deny. The neutrino flux from the sun has been consistently less theoretically calculated, for many decades now. The theory that tries to explain the shortage is the oscillation of the neutrino, the transformation of one type into another (electron to muon), the non-conservation of the lepton charge, respectively, the symmetry flying to the devil's grandmother and the triumph of the supporters of the Great Unification theories for which everyone is equal (but only at high energies) . But if neutrinos oscillate, then they have a non-zero (and different) mass. A non-zero neutrino mass will make life difficult for theoretical physicists, but astronomers will breathe freely - they do not have a debit with credit, the observed mass of the Universe is critically less than that required by the theory. And the “hidden” matter could then be honorably given to the power of the all-pervasive and elusive neutrinos that gained mass.
This concludes the popular science introduction to neutrino physics completed, if successful with the public, I can continue to recall my student years at the Physics Department :)
Source: https://habr.com/ru/post/75305/
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