Most particles disintegrate - but why?
Why do most particles disintegrate (and technically speaking, break up) into others?
Particle physics has already found a whole mountain of seemingly elementary particles, and there may be even more. But most of these particles do not lie quietly on the floor, waiting for us to sweep them. We needed to build special vehicles, such as the Large Hadron Collider, in order to produce them, open them and study them. Why? Because most of them - with the exception of those of which we ourselves are, and a couple of others - fall apart (fall apart) into other particles in a small fraction of a second. In fact, a small one - in comparison with it a millionth of a second seems like an eternity. Some of them survive the entire trillionth of a trillionth of a second, or even less!
In this article, using quite good, albeit imperfect, analogies, I'm going to give you a couple of explanations about why decay is the inevitable fate of most elementary particles.
')
You may recall that waves in the quantum world are made of particles; phonon sound waves, photon light waves, etc. Or you can just take it for granted and continue reading.
Decay for particles is like dispersion for waves, and you’re probably well acquainted with this effect.
Nothing lasts forever, including the sound of a hit string on a guitar or a hit on the note of the xylophone. And the wave is preceded by vibration. The xylophone guitar string or note vibrates as it moves back and forth. Why do you hear the sound, although the string is far from your ear? You hear it, because the string, vibrating in the air, makes the air itself vibrate, and creates waves moving through the air and reaching your ears, causing your eardrums to oscillate to and fro - and your brain turns this movement into a musical note.
Why does the sound of the string gradually die? When you hit a string, you spent a bit of energy, and part of the energy you used turned into the energy of a vibrating string. Energy is saved - it is not created and not destroyed, although it is able to move from place to place and change its nature. Little by little, the energy that manifests itself in the form of string vibrations disappears, transforming into other things. Part of it is lost to the vibration of the air, to sound waves. A part is lost to friction, and, consequently, to heat, that is, to the microscopic vibrations of molecules in the string and in the pegs holding it. This transformation of one type of vibration into a multitude of others and the transfer of energy from the large-scale movement of a vibrating string to other places is called dissipation. Dispersion occurs because the vibrating string touches and interacts with other objects, in particular, with air and pegs, and also because it has an internal structure.
The particles disintegrate according to the same scattering scheme, but quantum mechanics are already working here, which changes everything. Vibrations of the string gradually disappear, turning into wide sound waves and vibrations of crowds of atoms and molecules, and a typical particle can disintegrate into two, three, maximum four light-weight particles. This is just a quantum version of dispersion - the idea is the same, but with a quantum feature.
For example, a Higgs particle can suddenly decay into two particles of light (photons); Z-particle can suddenly fall into a muon and antimuon.
Rapidly disintegrating particles are called unstable; Particles that never decay are called stable. Particles that decay very slowly are often called metastable or long-lived — but these terms are relative, and their exact meaning depends on the context.
I had to cheat a little here. The phenomenon of decay of particles in the quantum world is really similar to the scattering of waves. But as an example of scattering, I described a similar and familiar to you, but not quite the phenomenon that is responsible for the majority of particle decays.
Almost all the particles known to us, disintegrate - and many very quickly. Of the stable particles, we only know the following in nature:
• Electron (and anti-electron);
• The lightest of the three types of neutrinos (and their antiparticles);
• Photon (self antiparticle);
• Graviton (which has not yet been found and is not foreseen in the near future, although gravitational waves have already been discovered).
There are also particles that are probably stable, but most likely just long-lived - and their lifetime is so long that only a small part of them could decay since the Big Bang. Among them:
• Other neutrinos (and antineutrinos — I will not mention further antiparticles, this will be implied);
• Proton (not an elementary particle);
• Many atomic nuclei.
Another long-lived particle is the neutron, which by itself, outside the atomic nucleus, lives for about 15 minutes. But neutrons inside atomic nuclei can live longer than the age of the Universe. The cores provide them with a stable home.
What determines the rate of decay of a particle? Let's see what determines the speed of dispersion of waves of a vibrating string. This should be related to the objects with which the string interacts (air, pegs, with itself) and how strongly it interacts with them. The air is easy to drive, so the string can sound long. But if you pull the string down into the water bath, its vibrations will subside much faster, because the string, creating waves in the water, will use up the vibratory energy faster. You yourself can speed up the dispersion by pressing a finger to the edge of the string. You will feel how the atoms and molecules of your finger will absorb this energy. Since you interact more strongly with other objects with the string, it is you who determine how the vibrations disappear. The harder you push the string, the more you interact with it, and the faster the sound quiets down.
What works in the dispersion of waves, works in the decay of particles. Some types of particles interact strongly with each other, some do not. For example, photons interact strongly with ordinary solid matter, so the Earth is opaque to light. Neutrinos interact with matter very weakly, so they usually fly through the Earth. Quarks interact strongly with each other, so they are always inside such composite particles as protons. But quarks interact with electrons very weakly, therefore electrons fly away from quarks - and therefore in atoms the electron orbitals are at a relatively large distance from the protons and neutrons that make up the tiny atomic nucleus.
Suppose a particle of one type (parent) can break up into two or more particles of other types. The stronger the interaction between these types of particles, the greater the likelihood of decay - and the more such decay is more common, and the less the lifetime of the parent particle. For example, the Higgs particle interacts very weakly with light, so its decay into two photons rarely occurs. But it interacts with W-particles much more strongly, and if it is heavy enough to decay into two W-particles, it almost always does.
So now you know that the fundamentals of the physical processes of the decay of particles are a quantum version of what you see in the outside world: the dispersion that occurs through vibrations. Now you know that the speed of dispersion is connected with the force of interaction of a vibrating object with others; likewise, particles interacting more strongly usually decompose faster than those interacting weaker. But this is not a complete picture. Quantum mechanics affects the decay of particles in a non-intuitive way, which does not coincide with our everyday experience, and is responsible for the fact that some particles do not decay at all or do it slowly. Fortunately, these properties can be described as a set of fairly simple rules.
Particle physics has already found a whole mountain of seemingly elementary particles, and there may be even more. But most of these particles do not lie quietly on the floor, waiting for us to sweep them. We needed to build special vehicles, such as the Large Hadron Collider, in order to produce them, open them and study them. Why? Because most of them - with the exception of those of which we ourselves are, and a couple of others - fall apart (fall apart) into other particles in a small fraction of a second. In fact, a small one - in comparison with it a millionth of a second seems like an eternity. Some of them survive the entire trillionth of a trillionth of a second, or even less!
In this article, using quite good, albeit imperfect, analogies, I'm going to give you a couple of explanations about why decay is the inevitable fate of most elementary particles.
')
You may recall that waves in the quantum world are made of particles; phonon sound waves, photon light waves, etc. Or you can just take it for granted and continue reading.
Decay for particles is like dispersion for waves, and you’re probably well acquainted with this effect.
Nothing lasts forever, including the sound of a hit string on a guitar or a hit on the note of the xylophone. And the wave is preceded by vibration. The xylophone guitar string or note vibrates as it moves back and forth. Why do you hear the sound, although the string is far from your ear? You hear it, because the string, vibrating in the air, makes the air itself vibrate, and creates waves moving through the air and reaching your ears, causing your eardrums to oscillate to and fro - and your brain turns this movement into a musical note.
Why does the sound of the string gradually die? When you hit a string, you spent a bit of energy, and part of the energy you used turned into the energy of a vibrating string. Energy is saved - it is not created and not destroyed, although it is able to move from place to place and change its nature. Little by little, the energy that manifests itself in the form of string vibrations disappears, transforming into other things. Part of it is lost to the vibration of the air, to sound waves. A part is lost to friction, and, consequently, to heat, that is, to the microscopic vibrations of molecules in the string and in the pegs holding it. This transformation of one type of vibration into a multitude of others and the transfer of energy from the large-scale movement of a vibrating string to other places is called dissipation. Dispersion occurs because the vibrating string touches and interacts with other objects, in particular, with air and pegs, and also because it has an internal structure.
The particles disintegrate according to the same scattering scheme, but quantum mechanics are already working here, which changes everything. Vibrations of the string gradually disappear, turning into wide sound waves and vibrations of crowds of atoms and molecules, and a typical particle can disintegrate into two, three, maximum four light-weight particles. This is just a quantum version of dispersion - the idea is the same, but with a quantum feature.
For example, a Higgs particle can suddenly decay into two particles of light (photons); Z-particle can suddenly fall into a muon and antimuon.
Rapidly disintegrating particles are called unstable; Particles that never decay are called stable. Particles that decay very slowly are often called metastable or long-lived — but these terms are relative, and their exact meaning depends on the context.
I had to cheat a little here. The phenomenon of decay of particles in the quantum world is really similar to the scattering of waves. But as an example of scattering, I described a similar and familiar to you, but not quite the phenomenon that is responsible for the majority of particle decays.
Almost all the particles known to us, disintegrate - and many very quickly. Of the stable particles, we only know the following in nature:
• Electron (and anti-electron);
• The lightest of the three types of neutrinos (and their antiparticles);
• Photon (self antiparticle);
• Graviton (which has not yet been found and is not foreseen in the near future, although gravitational waves have already been discovered).
There are also particles that are probably stable, but most likely just long-lived - and their lifetime is so long that only a small part of them could decay since the Big Bang. Among them:
• Other neutrinos (and antineutrinos — I will not mention further antiparticles, this will be implied);
• Proton (not an elementary particle);
• Many atomic nuclei.
Another long-lived particle is the neutron, which by itself, outside the atomic nucleus, lives for about 15 minutes. But neutrons inside atomic nuclei can live longer than the age of the Universe. The cores provide them with a stable home.
What determines the rate of decay of a particle? Let's see what determines the speed of dispersion of waves of a vibrating string. This should be related to the objects with which the string interacts (air, pegs, with itself) and how strongly it interacts with them. The air is easy to drive, so the string can sound long. But if you pull the string down into the water bath, its vibrations will subside much faster, because the string, creating waves in the water, will use up the vibratory energy faster. You yourself can speed up the dispersion by pressing a finger to the edge of the string. You will feel how the atoms and molecules of your finger will absorb this energy. Since you interact more strongly with other objects with the string, it is you who determine how the vibrations disappear. The harder you push the string, the more you interact with it, and the faster the sound quiets down.
What works in the dispersion of waves, works in the decay of particles. Some types of particles interact strongly with each other, some do not. For example, photons interact strongly with ordinary solid matter, so the Earth is opaque to light. Neutrinos interact with matter very weakly, so they usually fly through the Earth. Quarks interact strongly with each other, so they are always inside such composite particles as protons. But quarks interact with electrons very weakly, therefore electrons fly away from quarks - and therefore in atoms the electron orbitals are at a relatively large distance from the protons and neutrons that make up the tiny atomic nucleus.
Suppose a particle of one type (parent) can break up into two or more particles of other types. The stronger the interaction between these types of particles, the greater the likelihood of decay - and the more such decay is more common, and the less the lifetime of the parent particle. For example, the Higgs particle interacts very weakly with light, so its decay into two photons rarely occurs. But it interacts with W-particles much more strongly, and if it is heavy enough to decay into two W-particles, it almost always does.
So now you know that the fundamentals of the physical processes of the decay of particles are a quantum version of what you see in the outside world: the dispersion that occurs through vibrations. Now you know that the speed of dispersion is connected with the force of interaction of a vibrating object with others; likewise, particles interacting more strongly usually decompose faster than those interacting weaker. But this is not a complete picture. Quantum mechanics affects the decay of particles in a non-intuitive way, which does not coincide with our everyday experience, and is responsible for the fact that some particles do not decay at all or do it slowly. Fortunately, these properties can be described as a set of fairly simple rules.
Source: https://habr.com/ru/post/370481/
All Articles