Pion
lightest meson with a quark and an antiquark / From Wikipedia, the free encyclopedia
A pion or π meson is a meson, which is a subatomic particle made of one quark and one antiquark.
There are six types of quark (called flavours) but only two flavours go together to make a pion. These flavours are called up and down. Quarks have charge, so two quarks of the same flavour (both up or both down) make a neutral pion. But when the two quarks have different flavours (up and down), the pion will have a charge. This charge is positive when an up quark pairs with a down antiquark. The charge is negative when a down quark pairs with an up antiquark.
Pions do not exist for a long time. (On average, charged pions exist for around 26 nanoseconds; neutral pions last a tiny fraction of this). Pions are significant to our lives because they are one of the ways for strong force interactions to take place between nucleons like the protons and neutrons of ordinary matter. These interactions hold the nucleus together.
Pions are the lightest hadrons (particles made up of quarks) and pions with a positive or negative charge are the mesons with the longest mean lifetime (the average time that passes before they decay into leptons).