each of the lepton quantum numbers L., 4, andВ LT remains unchanged during the decay process of Eq, 45-13, their constant valuesВ being -I, 0, and 0, respectively. 45-13, so we mustВ have LT = 0 on each side. Thus, the net electron lepton number for these two particles on the right in Eq.В 45-13 is also zero the electron lepton number is also conserved in the process.В No members of the tau family appear on either side of Eq. The electron neutrino v.вЂ™ being a particle, has the electron number 4 =В + I. 45-13, theВ position, being an antiparticle (again see Table 45-2), has the electron lepton numberВ 4 = вЂ“ I. 45-13, so there theВ net electron lepton number must be 4 = o. = -I if they did not, the IJ.'вЂќwould not decay by this process.В No members of the electron family appear on the left in Eq.

45-13 have the same net muon lepton number-namely,В L. This leaves v.В on the right which, being an antiparticle, also has the muon lepton number L. do not belong to the muon family and thus have L. The IJ.+ is an antiparticleВ (see Table 45-2) and thus has the muon lepton number L. 45-8, which we now write more fully as.Д¬onsider this first in terms of the muon family of leptons. Remain unchanged during any particle interaction, This experimental fact is calledВ the law of conservation oC lepton number.В We can illustrate this law by reconsidering the antimuon decay process shownВ in Eq. In all particle interactions, the net lepton number for each family is IepalIlely c0nserved.Thus, there are actually three lepton numbers 4, L., L., and the net of each must. All other particles, which are not leptons, are assigned L = O. Each (normal)В particle in Table 45-2 is assigned L = +I and each antiparticle is assigned L = вЂ“ I. Leptons have no internal structure and noВ measurable dimensions they are believed to be truly pointlike fundamental particlesВ when they interact with other particles or with electromagnetic waves.ДЄccording-to experiment, particle interactions involving leptons obey a certain conservationВ law for a quantum number called the lepton number L. Furthermore, there are reasons to believe that there are only the three families of leptons shown in Table 45-2. Table 45-2 lists all the leptons (both particles and antiparticles) all have a spin quantum numbers of ].There are reasons for dividing the leptons into three families, each consistingВ of a particle (electron, muon, or tau), its associated neutrino, and the corresponding antiparticles. The tau has its own associated neutrino,В different still from the other two. another lepton, the tau, was discovered at SLAC in 1975 its discoverer, MartinВ Perl, shared the 1995 Nobel prize in physics. On the other hand, if electron neutrinos (pro used by the beta decay of fission products in a nuclear reactor)В strike a solid target, only tвЂ™electrons-and never muons-are produced. 45-7) strikes a solidВ target, only muons-and never electrons-are produced. We call the former the muonВ neutrino (symbol II.) and the latter the electron neutrino (symbol вЂњc) when it is necessary to distinguish between them.В These two types of neutrino are known to be different particles because, if aВ beam of muon neutrinos (produced from pion decay as in Eq. 45-7, associated with the production of a, is not the same particle as the neutrino produced in beta decay, associated with the appearance of an electron. PhysicistsВ gradually learned that the neutrino that appears in Eq. вЂThe move on,В whose decay is described in Eq. theВ familiar electron and the neutrino that accompanies it in beta decay. those particles onВ which the strong force does not act. we discuss some of the particles of one of our classificationВ schemes: lepton or hadron.

Lepton table