Whilst learning about the nature of subatomic particles, I came along a pion zero meson. What really stumbled me was that the quark configuration of the particles was up and anti-up or down and anti-down (strange and anti-strange). My question is why don't the quarks annihilate and how would a particle like that be created?

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    $\begingroup$ They do annihilate, that's why the particles decay, typically in less than a nanosecond. $\endgroup$ – knzhou Mar 1 '19 at 12:42
  • $\begingroup$ @knzhou Oh wow. Thank you very much! However, how would one be created? $\endgroup$ – steve_just_steve Mar 1 '19 at 12:54
  • $\begingroup$ @knzhou Looks like an answer to me $\endgroup$ – BioPhysicist Mar 2 '19 at 1:40

For matter and antimatter to annihilate, all the quantum numbers characterizing the two annihilating components have to add up to zero, so only same type can annihilate: proton-antiproton, electron-positron.

At the quark level for mesons it is just the $π^0$


where quark and antiquark can match and annihilate, leaving at first order the two photon decay channel.

However, how would one be created

It is created in primary interactions when the quantum numbers of quarks are matched up , depending on the probability of generating the particles. The charged mesons decay with the weak interaction, the $π^0$ quarks interact electromagnetically and lead to annihilation.

An example of a Feynman diagram where a $π^0$ can appear is below in the decay of a D meson:



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