In particle physics, the number of leptons is a conserved quantum number, representing the number of leptons in a basic particle reaction minus the number of anti leptons (the number of leptons is expressed in L, and for all leptons, L=+1; for all anti leptons, L=- 1; for particles other than leptons, L=0).[1]
Chinese name
Lepton number
Foreign name
Lepton number
Role
Characterize the equilibrium of basic particle reaction
Experimental and theoretical studies on the basic components of matter and their interactions have revealed many mysteries of the particle physics world.As we have known, there are two families of basic bricks that constitute all substances: leptons andquarkThey are all Fem particles.The interaction between quarks and leptons is transmitted by the gauge Bose particles,photontransmitElectromagnetic force，GluontransmitStrong，WAnd Z transferweak force。[2]
Lepton family
There are six kinds of particles in the lepton family.
There are six kinds of particles in the lepton familytaste, they have the following two important properties:
(2) The conservation of lepton number means that leptons can onlyparticleAntiparticleThe total number of leptons (the number of leptons minus the number of anti leptons) remains unchanged in all known physical processes.
Six known leptons with different flavors appear in pairs, each pair includes a charged lepton and a lepton calledneutrinoNeutral lepton.[2]
Lepton number
Announce
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Experiments show that the lepton number is conserved in the interaction.For example, the total number of leptons before reaction is+1, and the total number of leptons of particles generated after reaction is also+1.Different types of leptons, such as e-lepton (electron, VeLepton number and muon (muon, VμThe lepton number of () is also separately conserved in the experiment.
An additivity for describing the internal properties of particlesquantumNumber.It is recorded as L, and there are three electric lepton numbers Le, μ lepton number L μ and τ lepton number L τ.Le of electron e - and electron neutrino γ e is+1, and theirAntiparticleLe of e+sum is - 1, and Le of other particles is 0;L μ=+1 for μ - and γ μ, L μ=- 1 for their antiparticle μ+and γ e, and L μ=0 for other particles;τ particle number L of τ - and γ τ
=+1. Their antiparticles
+L of and γ e
=- 1, L of other particles
=0。Strong, electromagnetic and weak interactions involving leptons,Particle reactionOr in the process of decay, each lepton number is conserved.Lepton numberConservation forbids some processes that seem to happen.E.g. μ±→e±+The gamma process does not occur.[2]
Experimental findings
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In 1962, two kinds of neutrino V were found experimentallyeAnd VμThey are associated with electron and muon respectively, so the conservation of lepton number is decomposed intoNumber of electrons(e - and VeNumber of particles minus e+and VeNumber of particles) and number of muons (μ - and V μ number of particles minus μ+and VμNumber of particles) are respectively conserved.1975 MPellIn the e+e - collision experiment, a new lepton τ was found, which is negatively or positively charged,decayInto muons or electrons and two neutrinos.Its mass is 1776.99 MEV, nearly twice the mass of the proton, so it is also calledHeavy lepton。In 2000, neutrino V corresponding to τ particles was found experimentally
。Similarly, the number of τ leptons is also conserved in all processes involving leptons.except
In addition to particles, the first two types of leptons (e, VeAnd μ, Vμ）The properties of have been fully studied, and their properties are very similar, only the quality is very different, which explains this phenomenonParticle physicsAn important subject to be solved in theory.[3]
- The lepton number of the particle is+1, the lepton number of the corresponding antiparticle is - 1, and the lepton number of other non lepton particles is 0.For all reaction processes, the algebraic sum of the lepton number remains unchanged before and after the reaction, and the electron lepton number, muon lepton number and
The number of leptons remains unchanged.AndCharge conservationDifferent, the conservation of charge is related to the electromagnetic interaction, while the conservation of lepton number is not based on the known interaction, but it is found experimentally that it is always conservation.[3]
