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I've been reading about what happens when matter and antimatter collide, but have been unable to locate an explanation of how annihilation actually occurs.

I've now discovered that quarks and antiquarks may play a pivotal role in the annihilation process, though am unable to find further information.

Can someone please help?

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    $\begingroup$ Quarks and antiquarks have a role in the annihilation process of mesons and baryons with the irrespective antiparticle, but if we consider what is probably the most common annihilation process, i.e. electron and positron, which are leptons, quarks clearly do not play any role. $\endgroup$ Commented May 21, 2020 at 8:08
  • $\begingroup$ This is a good question and I have no answer to it. $\endgroup$
    – my2cts
    Commented May 28, 2020 at 16:57

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Annihilation is a fancy word to say that a particle and an anti-particle cease to exist, and become other particles. This process is a form of particle interaction.

For example, an electron (e⁻) and an anti-electron (positron, e⁺) annihilate creating a muon (μ⁻) and anti-muon (μ⁺), through a photon-exchange diagram.

enter image description here

To the question ¿how did the e⁺ and e⁻ disappear?: our intuition does not work for quantum mechanics. At the level of particle interactions, there is no such thing as "preservation of the initial colliding objects". Instead, we can think in terms of symmetries: the vertex e⁺/e⁻/γ is compatible with the underlying symmetries of the theory. Then if an electron and a positron touch they can become a photon (γ).*

Maybe you were reading about the annihilation of clusters of matter and antimatter. That could happen if there was aggregated antimatter in the cosmos, for which there is no evidence. In that case, there would be many many particle interactions, of which many would also be particle annihilations (e.g an electron found a positron or a quark found an anti-quark, and they convert into other particles). The final products of the big annihilation (the clusters of matter and anti-matter) would be mostly photons and other particles that travel freely through space, resembling a sort of explosion. This matches our common understanding of the term annihilation: some object existed and suddenly it doesn't exist anymore.

*This photon would not propagate freely through space, but convert into other particles very quickly.

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