Neutrino families

Estimates of primordial helium and deuterium abundance with Big Bang nucleosynthesis theory limit number of light neutrino families to 4 or less (Schramm et al). 

Up of quarks), electrons, and neutrinos. In addition to the electron, the only stable and isolatable particles are the proton and the neutrino. One may add the neutron, which decomposes into a proton, an electron, and an antineutrino when isolated. As the Dirac equation in free space does not refer to the charge (or the stability) of the electron, the only conditions for other particles to obey this equation are to have a rest mass and spin Vi. All that was said for the electron should then hold for these three particles, as well as for the others in the electron and neutrino families. 

It led to a prediction that the number of different sorts of neutrino (equivalent in standard particle physics to the number of families of quarks and leptons) is less than 4 and probably no more than 3. This prediction was subsequently confirmed (subject to slight reservations about differences between effective numbers of neutrino species in the laboratory and in the early Universe) by measurements of the width or lifetime of the Z° boson at CERN in 1990. 

A single parameter, the nucleonic density, is thus sufficient to explain the proportions of the light elements in the Universe, from helium at 10% of the number of hydrogen atoms to lithium at one ten-thousandth. However, the number of neutrino species must be at most three in order to avoid an overproduction of helium-4. Since each neutrino belongs to a single particle family, the number of particle farmlies in the Universe must... 

MUON. The muon (p ) is an elementary particle of the lepton family. Properties include Spin, mass (MeV). 105.66 lifetime, 2.20 x I0-6 second. The antiparticle is the positive muon (p1). The muon neutrino I n has spin. U 0 mass and is stable. The muon family appears to be simply... 

Another group of fundamental particles are the leptons (light particles), comprising also three families, electron and electron neutrino, muon and muon neutrino, tau particle and tau neutrino. Properties of the leptons are summarized in Table 3.3. The most important particles of this group are the electron and the electron neutrino, which are both stable. 

It is interesting, that heterotic string phenomenology embeds even in its simplest realisation both supersymmetric particles and the 4th family of quarks and leptons, in particular, the two types of WIMP candidates neutralinos and massive stable 4th neutrinos. So in the framework of this phenomenology the multicomponent analysis of WIMP effects is favorable. 

Figure 2. Cosmogenic neutrino flux of the family for various models Protheroe-Johnson (dashed line), Engel-Seckel-Stanev (dotted line), and the minimal (solid line) flux. (From Ahn, Cavaglih, Olinto 2003.)...

Neutrino - A stable elementary particle in the lepton family. Neutrinos have zero (or at least near-zero) rest mass and spin... 

The well-known proton, neutron, and electron are now thought to be members of a group that includes other fundamental particles that have been discovered or hypothesized by physicists. These very elemental particles, of which all matter is made, are now thought to belong to one of two families namely, quarks or leptons. Each of these two families consists of six particles. Also, there are four different force carriers that lead to interactions between particles. The six members or flavors of the quark family are called up, charm, top, down, strange, and bottom. The force carriers for the quarks are the gluon and the photon. The six members of the lepton family are the e neutrino, the mu neutrino, the tau neutrino, the electron, the muon particle, and the tau particle. The force carriers for these are the w boson and the z boson. Furthermore, it appears that each of these particles has an anti-particle that has an opposite electrical charge from the above particles. 

Elementary particles come in only two kinds quarks and leptons. There are only six quarks and six leptons, see Table 10.2. The leptons are the electron, e, the muon, fi, and the tauon (tau particle), t, and their respective neutrinos. The quarks and leptons are grouped together in three families (or generations) of two quarks and two leptons each. This makes 12 elementary building blocks, or 24 if one counts their anti particles Table 10.2 only refers to our matter (i.e. koino matter). The leptons and quarks all have different properties and names, sometimes also referred to as colors. The physical theory relating these particles to each other is therefore named Quantum Chromo Dynamics (QCD). 

All matter in nature belongs to the first family, which consist of two leptons, the electron and electron-neutrino, and the up-quark and the down-quark. The proton is made up of 2 up- and 1 down-quark, giving it a charge of +1 and mass 1, while the neutron is made up of 1 up- and 2 down-quarks giving it a charge of 0 and mass of 1 ... 

The second family in Table 10.2 contains the "heavy electron", the muon and the muon neutrino, and the charm and the strange quarks. The third family contains the tau particle, the tau electron, and the two quarks referred to as top (or truth) and bottom (or beauty). These quarks can only be produced in high energy particle reactions. 

In this zoo of particles, only the electron, which was discovered even before the atomic theory was proven and the atomic structure was known, is really unseeable, stable, and isolatable. The proton also is stable and isolatable, but it is made up of two quarks up (with charge -1-2/3) and one quark down (with charge —1/3). As for the quarks, while expected to be stable, they have not been isolated. The other particle constitutive of the atomic nucleus, the neutron, is also made up of three quarks, one up and two down, but it is not stable when isolated, decaying into a proton, an electron, and an antineutrino (with a 15-min lifetime). The fermions in each of the higher two classes of the electron family (muon and tau) and of the two quark families (strange charmed and bottom/top) are unstable (and not isolatable for the quarks). Only the elusive neutrinos in the three classes, which were postulated to ensure conservation laws in weak interaction processes, are also considered as being unseeable, stable, and isolatable. 

Known elementary constituents of matter are quarks and leptons (see Table 12.1). Three families have been discovered. In each family one has two flavors of quarks and one lepton with the associated neutrino. The decay of the free neutron observed in 1932 and described first by the Fermi theory of weak interactions is understood today as the decay of a d-quark (one of three quarks composing the neutron) into a u-quark (which forms the final proton with the unchanged other two quarks) and an electron plus its antineutrino. The particles participating in this process constitute the lightest (first) particle family of the Standard Model. 

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