threepion
Threepion refers to a hadronic system composed of three pions, the lightest mesons in the strong interaction: π+, π−, and π0. The three-pion system arises in a variety of processes and is used to study resonance formation, hadron dynamics, and the symmetries of quantum chromodynamics.
The three-pion state can carry total isospin I = 0, 1, 2, or 3, depending on the charge
Three-pion final states appear in several contexts, such as the decay of light-vector and axial-vector mesons
Theoretically, three-pion dynamics are described by chiral perturbation theory at low energies and by resonance models