two-meson theory

The two-meson theory emerged from attempts to explain the nuclear binding force, the strong interaction that holds atomic nuclei together. Early theories, like Werner Heisenberg's, proposed that protons and neutrons exchanged particles to maintain nuclear cohesion. However, these theories faced challenges. In 1935, Hideki Yukawa theorized a new particle, the meson, with a mass about 200 times that of an electron, to carry this force.1

The discovery of a particle in cosmic radiation with a mass similar to Yukawa's prediction initially seemed to confirm his theory. However, further research indicated this particle was too penetrating to be the direct carrier of the nuclear force. This led to the two-meson theory, which proposed that Yukawa's original meson (later identified as the pion) decayed into the observed, more penetrating particle (the muon). The pion is now understood as a meson composed of a quark and an antiquark, and it is sensitive to the strong force.12