High Quality Content by WIKIPEDIA articles! In particle physics, a pion (short for pi meson; denoted ?) is any of three subatomic particles: ?0, ?+ and ??. Pions are the lightest mesons and play an important role in explaining low-energy properties of the strong nuclear force.Pions have zero spin and are composed of first-generation quarks. In the quark model, an up quark and an anti-down quark compose a ?+, whereas a down quark and an anti-up quark compose the ??, which are antiparticles of one another. The uncharged pions are combinations of an up quark with an anti-up quark or a down quark with an anti-down quark, have identical quantum numbers, hence they are only found in superpositions.
