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In particle physics, a fermion is a subatomic particle that follows Fermi–Dirac statistics. Fermions have a half-odd-integer spin (spin 1/2, spin 3/2, etc.) and obey the Pauli exclusion principle.
Every elementary particle has associated with it a spin quantum number s (often called the spin number or just the spin), where s is any whole number multiple of a half. Fermions have half integral spin quantum numbers (½, 1½, 2½, etc.) and bosons have integral spin quantum numbers (0, 1, 2, etc.).
There are two main groups of particles in the Standard Model: bosons and fermions. This classification is based on an intrinsic property called spin, which, for elementary particles, can take the value 0, 1⁄2 or 1. Particles with integer spin (0, 1) are bosons, while those with half-integer spin (1⁄2) are fermions.
Fermions have half-integer spin; for all known elementary fermions this is 1 / 2 . All known fermions except neutrinos, are also Dirac fermions; that is, each known fermion has its own distinct antiparticle. It is not known whether the neutrino is a Dirac fermion or a Majorana fermion. [4] Fermions are the basic building blocks of all ...
Particles with half-integer spins, s = 1/2, 3/2, 5/2,... s = 1 / 2, 3 / 2, 5 / 2,..., are called fermions, while particles with integer spins, s = 0, 1, 2,… are called bosons. Fermions can only be created or destroyed in particle-antiparticle pairs, whereas bosons can be created or destroyed singly.
To calculate the T-matrix element a Feynman diagram, representing the amplitude to a given order in the perturbation series, can drawn. The Feynman diagram to first order for electron-muon scattering is given by All elements of the diagram, that is, external lines, internal lines and vertex factors have to be multiplied.
Particles that have half-integral spin— which includes the spin-1/2 electrons we’ve been talking about all this time— are fermions. Other fermions include protons, neutrons, quarks, and neutrinos.
