Elementary fermions electron

All electrons, protons and neutrons, the elementary constituents of atoms, are fermions and therefore intrinsically endowed with an amount h/2 of angular momentum, known as spin. Like mass and charge, the other properties of fermions, the nature of spin is poorly understood. In quantum theory spin is treated purely mathematically in terms of operators and spinors, without physical connotation. 

Every type of particle has a specific unique value of s, which is called the spin of that particle. The particle may be elementary, such as an electron, or composite but behaving as an elementary particle, such as an atomic nucleus. All 4He nuclei, for example, have spin 0 all electrons, protons, and neutrons have spin all photons and deuterons (2H nuclei) have spin 1 etc. Particles with spins 0, 1, 2,. .. are called bosons and those with spins are fermions. A many particle system of bosons behaves differently from a many... 

The half-spin of elementary waves (called fermions) appears as a chiral disturbance in the wave held and its mirror image has the opposite charge and anti-spin. An electron and its mirror equivalent, called positron, destroy each other on contact - all that remains is a high-energy photon ... 

The atomic theory of matter, which was conjectured on qualitative empirical grounds as early as the sixth century BC, was shown to be consistent with increasing experimental and theoretical developments since the seventeenth century AD, and definitely proven by the quantitative explanation of the Brownian motion by Einstein and Perrin early in the twentieth century [1], It then took no more than a century between the first measurements of the electron properties in 1896 and of the proton properties in 1919 and the explosion of the number of so-called elementary particles - and their antiparticles - observed in modern accelerators to several hundred (most of which are very short lived and some, not even isolated). Today, the standard model assumes all particles to be built from three groups of four basic fermions - some endowed with exotic characteristics - interacting through four basic forces mediated by bosons - usually with zero charge and mass and with integer spin [2],... 

Other elementary particles also have a characteristic spin. Those with half-integral spin quantum numbers are known as fermions and those with integral spin quantum numbers are known as bosons. The spin quantum numbers of a variety of particles are given in Table 5.2. When identical particles are interchanged, the wavefunctions associated with fermions and bosons behave differently, and this causes them to have significantly different properties. This will be discussed briefly in Chapter 7, where it is relevant to the way in which electron energy levels in atoms are filled. 

Eermions (particles with a spin of n ft/2 and n = odd integer) play an important role in many fields of physics, because aU stable elementary particles, such as electron, proton and neutron are Fermi particles with a spin of ft/2. Also atoms with a total angular momentum of n ft/2 (n = odd) are Fermions, such as the lithium isotope Li with a nuclear spin / = 1 ft and an electron spin s = ft/2, resulting in a total angular momentum of F = 3/2 ft or F = 1/2 ft. 

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. 

Pauli s Exclusion Principle The principle that no two identical elementary particles having half-integer spin (fermion) in any system can be in the same quantum state (i.e., have the same set of quantum numbers). In order to account for the various spectral characteristics of the different elements, one must assume that no two electrons in a given atom can have all four quantum numbers identical. This means that, in any orbit (circular, elliptical, or tilted), two electrons at most may be present and of these two, one must spin clockwise and the other must spin counterclockwise. Thus, the presence of two electrons of opposite spin in a given orbit excludes other electrons. 

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.)... 

The indistinguishability of elementary particles (such as photons or electrons) is an important concept suggesting the division of all known elementary particles into two classes Bosons and Fermions. Indistinguishable means that the Hamiltonian operator commutes with another operator that interchanges two particles in a system. This leads to the conclusion that elementary particles in nature may simultaneously... 

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