How does collision of particles create more particles?

Question

I mean, how do real particles get created in a collider like the LHC?

Is it right that the LHC just gives energy to a pair of virtual particles that were generated by the quantum vacuum making them real particles?

Answer 1

I think it is different than you imagine. In particle collisions there are no 'virtual particles created by the vacuum' involved. Not in the sense that there are 'virtual particles that arise as quantum fluctuations from the vacuum present and (somehow) interact with the particles in the collider', if this is what you mean.

There are virtual particles involved, but these are the particles that pop up in calculations in quantum field theory to describe, if you will, intermediate states between the incoming and outgoing real particles in particle interactions.

If you saw Feynman diagrams before, you saw them. The virtual particles are all particles that are represented by internal lines, not leaving the diagram as incoming or outgoing particles. They arise because the calculation actually is a perturbative calculation... It is an approximation to a process determined by the full theory that we can not calculate exactly. The closer you want the approximation to be to the real process, the more internal, i.e. virtual particles will be involved in the calculation grossing over a lot of details, for example of renormalisation here). It is more or a less a philosophical question, I think, what they actually represent.

Let's give an example: A positron and an electron can annihilate and form a virtual photon which than forms a muon and an anti-muon. This virtual photon was not created by the vacuum, but by the positron-electron pair. The energy in the resulting muons comes from the rest energy and kinetic energy of the positron and electron (and it has to be a lot of kinetic energy, since the muon is much heavier, i.e. has a larger rest energy than the electron), not from the vacuum. Which real/virtual particles can create, i.e. interact with, which particles is described by the Lagrangian of the respective quantum field theory. This determines which diagrams with which internal particles are possible and have to be considered for higher order calculations.