I am reading about some old discoveries in particle physics and early collider experiments from Perkin's Introduction to High Energy Physics. However, I didn't get the answers to all my questions.
If two beams of electrons and positrons are collided head-on, the collision can produce various quark-antiquark meson states called quarkonium. For example, $e^-e^+$ annihilations have produced various $c\bar{c}$ and $b\bar{b}$ meson bound states came to be collectively known as charmonium and bottomonium respectively. The most stable charmonimum is $J/\psi$ and bottomonium is $\Upsilon$. Toponium states do not exist since top quarks decay too fast to form mesons. The also exists bound states of $e^+e^-$ and $\mu^+\mu^-$, respectively called positronium and muonium.
If particles and antiparticles annihilate each other how can there be a bound state of them in the first place?