Particle composition vs particle decay

In summary, the conversation discusses the concept of elementary particles and their ability to decay into other particles. The main questions revolve around whether or not we can say that an elementary particle is composed of the particles it decays into, and if an elementary particle can be created through decay. The conversation also touches on the idea of particles being made of energy and field balances, and the concept of decay vs. scattering in quantum field theory. The conclusion is that elementary particles are fundamental and indivisible, and their decay is more like a transformation or metamorphosis rather than a breaking apart into smaller pieces.
  • #1
pftest
249
0
Ive read that elementary particles can decay. I am trying to understand how this can be with a particle that has no composition. So i have two questions:

If elementary particle A decays into particles B and C, then why can't we say that A is composed of B and C?

If an elementary particle can decay, does it mean it can be created also? Is there a specific term for this process?
 
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  • #2
pftest said:
If elementary particle A decays into particles B and C, then why can't we say that A is composed of B and C?

Are particles B and C elementary particles?
 
  • #3
Yes, they are elementary particles. A muon decays to 1 electron + 2 neutrinos.
 
  • #4
Ah, I think I misunderstood a little. Surely A WOULD be composed of B and C?
 
  • #5
T=0 said:
Ah, I think I misunderstood a little. Surely A WOULD be composed of B and C?
Thats what you would think, but A is also an elementary particle, it has no composition.
 
  • #6
pftest, For one thing, elementary particles appear to have no structure - they are to the best of our knowledge pointlike, and therefore not made of any smaller pieces.

For another, there is no consistent way to assign the pieces.

e+ + e- → γ + γ

Where did the photons come from? And where did the electrons go? Which is made of what?

p + p → p + p + π+ + π-

Where did the pions come from? Protons would seem to have an indefinite supply of pions.

π+ → μ+ + νμ

But sometimes

π+ → e+ + νe

What is the pion "made of", an electron or a muon?

There is no way to assign the pieces consistently. One has to conclude that there are no pieces - particles simply turn into other particles.
 
  • #7
Indeed, there are a few rare cases where both the decays A -> B + C and B -> A + C are allowed. (A and B are very broad, and C is a pion)
 
  • #8
After some thinking, it seems that it is not so much decaying so much as metamorphosis. It looks as if, for instance, the muon transforms into an electron and 2 neutrinos. This would also explain your other question, if turned around. Remember Einstein's equation, e=mc2, this implies that mass can become energy, and vice-versa, so I believe that this might have something to do with it.
 
  • #9
everything is composed of energy and field balances. any set of partcles and matching antiparticles may be made from a source of free energy, such as kinetic energy of an accelerated electron.
furthermore, as long as all the balances are met, there is no reason that any group of particles adding up to the total mass-energy, spin, color, etc... can be created from nothing.

"elementary" merely means it is indivisible in its rest state; if its rest state is excited in some manner, then it will decay (like a strange quark, or a Tau lepton) but it is still a fundamental and indivisible particle before it decays.
 
  • #10
What's weird is that there is little difference between decay and scattering in Quantum field theory (or at least in the Feynman diagram approach). You can connect interaction vertices like you want and many and more combinations are valid physical phenomena. Many are forbidden by kinematics or some conservation law, but I find it deeply fascinating and quite intriguing that you can basically play Lego with particles.
 

What is particle composition?

Particle composition refers to the types and amounts of different particles that make up a substance.

What is particle decay?

Particle decay is the process by which unstable particles break down into smaller, more stable particles.

What is the difference between particle composition and particle decay?

Particle composition describes the makeup of a substance, while particle decay refers to the changes that occur within a substance as unstable particles break down into more stable particles.

How do scientists study particle composition and particle decay?

Scientists use various techniques, such as particle accelerators and detectors, to study the properties and behavior of particles and their decay processes.

What are some real-world applications of understanding particle composition and particle decay?

Understanding particle composition and decay can help scientists develop new materials, improve medical imaging techniques, and gain a better understanding of the fundamental building blocks of our universe.

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