Elementary fermions leptons

Presently we consider the quarks, which come in six different flavours, and the leptons, of which also six have been identified, as elementary fermions. 

On the other hand, no sign of baryon number violation has been observed to date in any elementary particle physics experiment. In the Standard Model, one cannot find any process that would involve the transformation of a proton into mesons or leptons. However, in the early 1970s, t Hooft (1976) showed that in the presence of specific configurations of electro-weak vector fields, fermions (leptons and quarks) can be created or annihilated, but the difference of the baryon number and of lepton number B—L) should stay constant (quarks and antiquarks actually carry 1/3 unit of baryon charge, while the lepton charge of the known species is 1). Today the chance for such transitions to occur is negligible (the probability is estimated to about 10 ). However, they must have occurred frequently when the temperature was of the order of 100 GeV (about 10 K). 

The name phlogiston was chosen for a bound electron because the alternative proposed, gluon,is already in use by elementary particle physicists for a different particle and also because the word phlogiston already has the form (with the suffix -on) that is usual for the names of elementary particles in physics. Elementary particles such as electrons, photons, tachyons, mesons, fermions, neutrons, leptons, and so on are examples of that syntax. Phlogistons then are localized renormalized chemical electrons. They behave quite like a liquid, and that electron liquid could be called phlogiston. 

Abstract The present experimental evidence seems to support the Standard Model of elementary particles, which interprets the world as consisting of 12 basic fermions six quarks and six leptons with their antiparticles, 13 hosons mediating the strong, electromagnetic and weak interactions, and the mysterious Hi s hoson. This chapter attempts to overview the basic features of the Standard Model with a minimal mathematical apparatus. 

Later it was also found that there were other elementary particles that had halfintegral spins such as particles in the class of leptons (e.g., electrons, muons), baryons (e.g., neutrons, protons, lambda particles), and nuclei of odd mass number (e.g., tritium, helium-3, uranium-233). All particles with half-integral units angular momenta are classified as fermions and obey Fermi-Dirac statistics whereas particles with integral units of angular momenta, e.g., photons and nuclei of even mass number, are classified as bosons and obey Bose-Einstein statistics. (See Chapter 15 for further detail.)... 

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