sci.physics.particle

On Feb 28, 8:19=A0am, omega wrote:
> Every meson is composed of a quark and an antiquark. And a pion is
> composed of an up quark and an up antiquark. But antimatter will
> annihilate matter. How could these two particles stay closely yet
> peacefully?
>
> P.S It's my first time to use this web. Can any one tell me how to
> type expressions here like up antiquark? Thank you very much!

A good explanation is at...
http://en.wikipedia.org/wiki/Pion.

Essentially the neutral pion is a superposition of an up - antidown -
down - antiup quarks.
Relative to the charged pions, they don't last long. There is no pion
which is purely a mixture like
up-antiup or down-antidown.