pair production.?

Question

why pair production need to be happen in an enviornment that include mass?

Answer 1

It's a kinematic problem. You need something that can carry away some energy and momentum in order to create the phase space necessary for the reaction.

Otherwise, if a single photon just turns into an e+ e- pair, their energy and momenta can't be completely specified.

The cross section for a reaction is proportional to the phase space. No phase space means no cross section. The reaction won't happen.

Edit--virtual pair production can happen in a vacuum you allow for momentary non-conservation of energy/momentum, but the virtual pairs can't stick around long enough for you to see them. The vacuum fluctuations do produce a tiny correction to the photon propagator. Real pair production requires something to carry off momentum.

Answer 2

Conservation of momentum. the mild is going in a unmarried direction, let's call it z and use the classic Cartesian foundation. If both of the debris have ANY x or ANY y element, their corresponding antiparticle must have an equivalent and opposite element, with the intention to guard momentum. so as that they separate. Draw a photo with the axes in if that helps?! even if or not they don't have any x or y element, they ought to have distinct z factors of momentum and for this reason separate, because otherwise that they had be 'on top' of one yet another promptly and there might want to be no pair production (or in case you've carried out Feynman diagrams, you'll have imaginary particle-antiparticle pairs in a 'loop', that you will be able to't be conscious). often times they don't have adequate momentum, and they swing decrease back mutually and annihilate at a later time.

Answer 3

I can give you an equation-based answer.
Think momentum. If you have an electron and a positon travelling through space, you can always find a frame of reference that has them going the opposite ways, with the same speed. In that frame of reference the total momentum is 0. But all processes conserve momentum. So if we just want the photon before the creation, it would have to have a momentum of 0 in that frame of reference. Which is impossible, such a photon would have 0 energy, so no potential to create a pair. So the process photon->electron+positon is not allowed because of kinematics.
so we need another body - electron, proton, nucleus, whatever to carry off some of the photon's momentum, getting the reaction photon+object->electron+positon+object moving differently. And this is allowed.
Hope it helps.

Answer 4

Hi. It doesn't. Particle / anti-particle formation and collapse occurs in a vacuum as well as in or near mass.