Pion

Pi mesons have zero spin and are composed of first generation quarks. An up and an anti-down quark compose a pi-plus, while a down and an anti-up quark compose the pi-minus, its antiparticle. Combinations of up and anti-up, or down and anti-down, would both be neutral, but because they have the same quantum numbers are only found in superpositions. The lowest energy superposition is the pi-zero, and it is its own antiparticle.

The pi-plus (π⁺) and pi-minus (π^-) may combine to form an exotic atom called pionium, if they are created close to each other with a small relative momentum.

External Link

• http://hyperphysics.phy-astr.gsu.edu/hbase/particles/hadron