Meson could include both matter and antimatter?

I wonder eta and pion could exist containing up quark (anti up quark)? Isn't there pair annihilation in this meson?

• Hi HERO, and welcome to Physics Stack Exchange! I've removed a number of comments that were attempting to answer the question and/or responses to them. Commenters, please keep in mind that comments should be used for suggesting improvements and requesting clarification on the question, not for answering. Jul 2 '20 at 16:54

The neutral pion has its valence quarks (which include your $$\bar u u$$) annihilate each other to produce two photons, in less than $$10^{-16}$$ s.
• but for pion+ known as $\pi^+$, do we have $u \overline{d}$ which already contains the antimatter $\overline{d}$? also +1 I voted up Jul 6 '20 at 15:04
• The $\pi^+$ is 8 orders of magnitude longer lived than the $\pi^0$, since it decays weakly instead of electromagnetically, via a virtual $W^+$. That is, the $\bar d$ annihilates the u, maintaining B=0, quite nicely. All mesons are unstable, as they should be. Jul 6 '20 at 15:12