How Do Photon Collisions Lead to Particle-Antiparticle Pair Production?

[Deepak247]

I recently read a post which stated that the particle-antiparticle pair can be created by the interaction of photons

"2 GeV is a threshold for proton-antiproton pair production, for example through photon collisions"

I want to know more on these types of photons, their classifications and a brief overview of the whole process...how and when it carried in the universe?

 

[tom.stoer]

A typical process is the photo-pion production where ONE photons scatters with a proton which stays intact and which is only required for energy-momentum conservation; the photon is then convertet into a pion-antipion pair:

$$\gamma + p \to \pi^+\pi^- + p^\prime$$

This process is possible for all charged particles like proton, e.g. with a heavy nucleus instead of a proton. It also works for other particle-antiparticle pairs like electon + positron.

In addition one could think about a process like

$$2\gamma \to X\,\bar{X}$$

where a particle-antiparticle pair (denoted by the X) is created from a photon pair. This process is allowed for every charged particle X but it is highly suppressed and cannot be observed directly. This is clear as we know that classically light does not interact with light at all (take two LASER beams, they do not affect each other).

Now coming back to your question where you take a photon pair and convert it into a proton-antiproton pair, i.e. where the unspecified X is replaced with a p.

$$2\gamma \to p\,\bar{p}$$

There is a threashold for this process which can be determined as follows: The final state energy is the sum of the energy of the proton-antiproton pair. The minimum energy required is 2Mc² where M is the proton mass; this happens when the proton and the antiproton are created at rest. For a proton-antiproton pair with non-vanishing momentum each particle would carry E=Mc² + some kinetic energy; so to determine the threshold we set the momentum and therefore the kinetic energy to zero.

So the threshold is

$$E_\text{thresh} = 2M_pc^2$$

which means that each photon carries total energy which is equal to the proton's rest energy

$$E_\gamma = E_{p, \text{rest}} = M_pc^2$$

 

[A. Neumaier]

I recently read a post which stated that the particle-antiparticle pair can be created by the interaction of photons

"2 GeV is a threshold for proton-antiproton pair production, for example through photon collisions"

I want to know more on these types of photons, their classifications and a brief overview of the whole process...how and when it carried in the universe?

See the article discussed in the entry ''Can virtual particles become real? A case study''
in Chapter A7 of my theoretical physics FAQ at http://arnold-neumaier.at/physfaq/physics-faq.html#becomeReal