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Pi meson, also known as a pion, is an elementary particle belonging to the meson family. Pions are composed of a quark and an antiquark, and they play a crucial role in the strong nuclear force, which binds protons and neutrons together in atomic nuclei. Pions are classified into three types based on their quark content: positively charged pions (π+), negatively charged pions (π-), and neutral pions (π0).