The fact that the above decay is a three-particle decay is an example of the conservation of lepton number there must be one electron neutrino and one muon neutrino or antineutrino in the decay. The muon is a lepton which decays to form an electron or positron. What evidence suggests that the electron is a fundamental particle? Associated with the electron is the electron neutrino. On the other hand, one of the mechanisms for the interaction of radiation with matter is the pair production of an electron-positron pair. If an electron and a positron encounter each other, they will annihilate with the production of two gamma-rays. The electron's antiparticle, the positron, is identical in mass but has a positive charge. It is a fermion of spin 1/2 and therefore constrained by the Pauli exclusion principle, a fact that has key implications for the building up of the periodic table of elements. Table of lepton propertiesĪs one of the leptons, the electron is viewed as one of the fundamental particles. The observed abundance agrees with three types of neutrinos. When the process of nucleosynthesis from the big bang is modeled, the number of types of neutrinos affects the abundance of helium. One of the pieces of experimental evidence for that is the measured hydrogen/helium abundance ratio in the universe. The present standard model assumes that there are no more than three generations. Now that we have experimental evidence for six leptons, a relevant question is "Are there more?". Important principles for all particle interactions are the conservation of lepton number and the conservation of baryon number. The different varieties of the elementary particles are commonly called "flavors", and the neutrinos here are considered to have distinctly different flavor. There are six leptons in the present structure, the electron, muon, and tau particles and their associated neutrinos. Leptons and quarks are the basic building blocks of matter, i.e., they are seen as the "elementary particles".
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