4/12/2023 0 Comments Lepton numberMøller, I adopt - as a pendant to "nucleon" - the denomination "lepton" (from λεπτός, small, thin, delicate) to denote a particle of small mass. The names "mu" and "tau" seem to have been selected due to their places in the Greek alphabet mu is seven letters after epsilon (electron), whereas tau is seven letters after mu.Īccording to the Oxford English Dictionary, the name "lepton" (from Greek leptos) was first used by physicist Léon Rosenfeld in 1948:įollowing a suggestion of Prof. two (or three) of the neutrinos are heavier than 0.008 eV.one (or more) of the neutrinos is heavier than 0.040 eV.ν μ and ν τ are lighter than 2.2 eV (as ν e is and the mass differences between the neutrinos are of order of millielectronvolts).However there have been measured (indirectly based on the oscillation periods) the differences of the mass squares between the neutrinos, which have been estimatedĪnd. Note that the neutrino masses are known to be non-zero because of neutrino oscillation, but their masses are sufficiently light that they have not been measured directly as of 2007. Table of the leptons Charged lepton / antiparticleĮlectron neutrino / Electron antineutrino This property is called lepton universality and has been tested in measurements of the tau and muon lifetimes and of Z-boson partial decay widths, particularly at the SLC and LEP experiments. The couplings of the leptons to gauge bosons are flavor-independent. A much stronger conservation law is the total number of leptons of all flavors, which is violated by a tiny amount in the Standard Model by the so-called chiral anomaly. Conservation of the number of leptons of different flavors (for example, electron number or muon number) may sometimes be violated (as in neutrino oscillation). This principle is known as conservation of lepton number. When particles interact, generally the number of leptons of the same type (electrons and electron neutrinos, muons and muon neutrinos, tau leptons and tau neutrinos) remains the same. The masses of the leptons also obey a simple relation, known as the Koide formula, but at present this relationship cannot be explained. The charged leptons have two possible spin states, while only one helicity is observed for the neutrinos (all the neutrinos are left-handed, and all the antineutrinos are right-handed). All known charged leptons have a single unit of negative or positive electric charge (depending on whether they are particles or antiparticles) and all of the neutrinos and antineutrinos have zero electric charge. All six of these particles have corresponding antiparticles (such as the positron or the electron antineutrino). The other is a nearly massless neutral particle called a neutrino (such as the electron neutrino). One is a massive charged particle that bears the same name as its flavor (like the electron). Each flavor is represented by a pair of particles called a weak doublet. There are three known flavors of lepton: the electron, the muon, and the tau.
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