Charged pions decay into muons and muon neutrinos whereas neutral pions decay into gamma rays. Examples of mesons commonly produced in particle physics experiments include pions and kaons. Fermi conducted important research in particle physics, especially related to pions and muons. The neutrinos from subsequent decays of pions and kaons form the neutrino beam. At first, quarks are still confined and we create a gas of hadrons (pions, mostly). The neutral pions formula 1 decay into photons formula 2 in a process formula 3. The technique is to collide protons with a fixed target, producing charged pions or kaons. The Goldstone bosons corresponding to the three broken generators are the three pions. An antiproton typically annihilates into a few charged or neutral pions. The neutral pions will decay immediately into gamma rays. However, in the quark model, the rhos are excited states of pions. Together, the pions form a triplet of isospin. The K must decay into three pions. Pionium, a bound state of two oppositely-charged pions, is useful for exploring the strong interaction. Pionium, a bound state of two oppositely-charged pions, is interesting for exploring the strong interaction.