Discovery of the Muon

The muon was discovered in 1937 by J. C. Street and E. C. Stevenson in a cloud chamber. The discovery was published in "New Evidence for the Existence of a Particle Intermediate Between the Proton and Electron", Phys. Rev. 52, 1003 (1937). Before this point the fundamental particles were presumed to be electrons, protons and the (then) newly discovered neutron. The discovery brought attention to the prediction by Hideki Yukawa in 1935 that an intermediate mass "meson" might be responsible for the nuclear strong force. Yukawa had predicted a mass of about 100 MeV/c² and the muon had a mass very close to that. It was soon discovered, however, that the muon did not participate in the strong interaction at all. Hans Bethe and Robert Marshak suggested that the muon might be the decay product of the particle needed in the Yukawa theory, so the search continued. That search led to the discovery of the pion.

μ子于1937年由J. C. Street和E. C. Stevenson在云室中发现。这一发现发表于《New Evidence for the Existence of a Particle Intermediate Between the Proton and Electron》，Phys. Rev. 52, 1003 (1937)。在这一发现之前，基本粒子被认为仅包括电子、质子和当时刚刚被发现的中子。这一发现引起了对Hideki Yukawa在1935年提出的预测的关注，即一种中间质量的“介子”可能负责核强相互作用。Yukawa预测了约100 MeV/c²的质量，而μ子的质量非常接近。然而不久之后发现，μ子根本不参与强相互作用。Bethe和Marshak建议μ子可能是Yukawa理论中所需粒子的衰变产物，因此搜索继续进行。这一搜索最终导致了π介子的发现。