Regarding pair production and annihilation

In summary, the conversation discusses the theoretical possibility of creating an infinite amount of positron and electron pairs through the process of pair annihilation and production. The speakers also touch on the role of photons as force carriers for the EM force and W/Z bosons for the weak force, and how their properties are defined by the theory of the electroweak force. Additionally, they mention how energy and momentum must be conserved in order to create an electron-positron pair with a photon, and how this process is easier near high-Z nuclei due to their ability to carry away momentum.
  • #1
Squall94
6
0
Hi, i have a few questions about these two processes. Now, I am only 16 years old, in my last year of school, so I am not so familiar with physics, if you could put terms simple enough for an average 16 year old to understand, i'd much appreciate it :)
my question is:
If e‾ + e+ → γ + γ and γ → e‾ + e+, wouldn't that mean its theoretically possible to produce almost an infinite amount of positron and electron pairs? What i mean is annihilate a pair, force both gamma rays to undergo pair production, keep one e-/e+ pair, and annihilate the other?

on a side note, why exactly are photons the force carriers for EM force, and W/Z bosons the force carriers for weak force?
 
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  • #2
Throughout all these reactions, energy must be conserved. In order for pair creation to happen, the photon must have at least enough energy to create the two particles (2 times 0.511 MeV). So you can certainly turn the kinetic energy of the original pair into additional pairs of particles (if it exceeds the mass threshold), in fact, that is the principle behind some calorimeters (detectors that measure energy) used in particle physics, for example at the LHC.
 
  • #3
Squall94 said:
on a side note, why exactly are photons the force carriers for EM force, and W/Z bosons the force carriers for weak force?
The force carries for the EM force are called "photons", and the force carriers for the weak force are called "W+, W-, Z". The names are just definitions.

If you ask why they have their properties (and why the weak force has 3 particles): Well, first, it is an observation. Based on this observation, the theory of the electroweak force was developed, and with this theory it is possible to calculate the properties of these particles (more properties than the theory needed as input ;)).
 
  • #4
In order to create an electron-positron pair with a photon, BOTH energy AND momentum have to be conserved. This not possible in vacuum, but it is possible in the Coulomb field of a nucleus, because the heavy nucleus can carry away a lot of momentum with only a small amount of energy loss. It is much easier to create electron positron pairs with photons over about 2 MeV (threshold 1.02 MeV) near high-Z nuclei, like lead, for example, than copper.
 

1. What is pair production and annihilation?

Pair production and annihilation are two processes in quantum mechanics that involve the creation and destruction of particle-antiparticle pairs. Pair production occurs when a high-energy photon (such as a gamma ray) interacts with a nucleus, producing an electron-positron pair. Annihilation is the opposite process, where a particle and its antiparticle collide and are converted into energy in the form of photons.

2. How does pair production and annihilation relate to Einstein's famous equation E=mc^2?

Einstein's equation states that energy (E) is equal to mass (m) multiplied by the speed of light (c) squared. In pair production, the high-energy photon has enough energy to create a particle-antiparticle pair, which then has mass due to its energy. In annihilation, the opposite occurs and the mass of the particle-antiparticle pair is converted back into energy.

3. What is the significance of pair production and annihilation in particle physics?

Pair production and annihilation are important processes in particle physics because they demonstrate the relationship between mass and energy, as well as the existence of antiparticles. They also play a crucial role in the study of high-energy phenomena, such as particle accelerators and the early universe.

4. Can pair production and annihilation occur in a vacuum?

Yes, pair production and annihilation can occur in a vacuum as long as there is enough energy present. In a vacuum, there are no particles or antiparticles present, but if a high-energy photon or other particles come into contact with the vacuum, they can create particle-antiparticle pairs.

5. How are pair production and annihilation related to the conservation of energy and momentum?

Pair production and annihilation both obey the laws of conservation of energy and momentum. In pair production, the total energy and momentum of the initial photon are conserved in the creation of the particle-antiparticle pair. In annihilation, the total energy and momentum of the particles and antiparticles involved are conserved in their conversion into photons.

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