Thomson and his team of British physicists in 1897. The first lepton identified was the electron, discovered by J.J. However, the mass of the tau (discovered in the mid-1970s) ( 1777 MeV/ c 2) is nearly twice that of the proton and about 3,500 times that of the electron.Ī muon transmutes into a muon neutrino by emitting aīoson subsequently decays into an electron and an electron antineutrino. Rosenfeld chose the name because the only known leptons at the time were electrons and muons, whose masses are small compared to nucleons-the mass of an electron ( 0.511 MeV/ c 2) and the mass of a muon (with a value of 105.7 MeV/ c 2) are fractions of the mass of the 'heavy' proton ( 938.3 MeV/ c 2). Møller, I adopt-as a pendant to 'nucleon'-the denomination 'lepton' (from λεπτός, small, thin, delicate) to denote a particle of small mass. Lepton was first used by physicist Léon Rosenfeld in 1948: įollowing a suggestion of Prof. The name lepton comes from the Greek λεπτός leptós, 'fine, small, thin' ( neuter nominative/accusative singular form: λεπτόν leptón) the earliest attested form of the word is the Mycenaean Greek 𐀩𐀡𐀵, re-po-to, written in Linear B syllabic script. Exotic atoms with muons and taus instead of electrons can also be synthesized, as well as lepton–antilepton particles such as positronium. Electrons are one of the components of atoms, alongside protons and neutrons. Leptons are an important part of the Standard Model. The tau neutrino remained elusive until July 2000, when the DONUT collaboration from Fermilab announced its discovery. Lederman, Melvin Schwartz, and Jack Steinberger, and the tau discovered between 19 by Martin Lewis Perl and his colleagues from the Stanford Linear Accelerator Center and Lawrence Berkeley National Laboratory. The muon neutrino was discovered in 1962 by Leon M. It was first observed in the Cowan–Reines neutrino experiment conducted by Clyde Cowan and Frederick Reines in 1956. The first neutrino, the electron neutrino, was proposed by Wolfgang Pauli in 1930 to explain certain characteristics of beta decay. It took until 1947 for the concept of 'leptons' as a family of particles to be proposed. After investigation, it was realized that the muon did not have the expected properties of a meson, but rather behaved like an electron, only with higher mass. Anderson in 1936, which was classified as a meson at the time. The next lepton to be observed was the muon, discovered by Carl D. The first charged lepton, the electron, was theorized in the mid-19th century by several scientists and was discovered in 1897 by J. It is not currently known whether this is the case. According to certain theories, neutrinos may be their own antiparticle. Unlike quarks, however, leptons are not subject to the strong interaction, but they are subject to the other three fundamental interactions: gravitation, the weak interaction, and to electromagnetism, of which the latter is proportional to charge, and is thus zero for the electrically neutral neutrinos.įor every lepton flavor, there is a corresponding type of antiparticle, known as an antilepton, that differs from the lepton only in that some of its properties have equal magnitude but opposite sign. Leptons have various intrinsic properties, including electric charge, spin, and mass. Thus electrons are stable and the most common charged lepton in the universe, whereas muons and taus can only be produced in high energy collisions (such as those involving cosmic rays and those carried out in particle accelerators). The heavier muons and taus will rapidly change into electrons and neutrinos through a process of particle decay: the transformation from a higher mass state to a lower mass state. Electrons have the least mass of all the charged leptons.

Μ) and the third are the tauonic leptons, comprising the tau ( The first-generation leptons, also called electronic leptons, comprise the electron (Į) the second are the muonic leptons, comprising the muon ( There are six types of leptons, known as flavours, grouped in three generations. The best known of all leptons is the electron. Charged leptons can combine with other particles to form various composite particles such as atoms and positronium, while neutrinos rarely interact with anything, and are consequently rarely observed. Two main classes of leptons exist: charged leptons (also known as the electron-like leptons or muons), and neutral leptons (better known as neutrinos). In particle physics, a lepton is an elementary particle of half-integer spin ( spin 1⁄ 2) that does not undergo strong interactions. Without proper rendering support, you may see question marks, boxes, or other symbols. This article contains special characters.

Lepton site