# Spin (physics)

spinnuclear spinspinsspin multiplicityspin operatorquantum spinspin stateelectron spinspin angular momentumnuclear spins
In quantum mechanics and particle physics, spin is an intrinsic form of angular momentum carried by elementary particles, composite particles (hadrons), and atomic nuclei.wikipedia
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### Spin quantum number

spinspin numberelectron spin
All elementary particles of a given kind have the same magnitude of spin angular momentum, which is indicated by assigning the particle a spin quantum number.
In atomic physics, the spin quantum number is a quantum number that parameterizes the intrinsic angular momentum (or spin angular momentum, or simply spin) of a given particle.

### Spin–statistics theorem

spin-statistics theoremSpin Statistics TheoremBecause mesons are bosons
When combined with the spin-statistics theorem, the spin of electrons results in the Pauli exclusion principle, which in turn underlies the periodic table of chemical elements.
In quantum mechanics, the spin–statistics theorem relates the intrinsic spin of a particle (angular momentum not due to the orbital motion) to the particle statistics it obeys.

### Pauli exclusion principle

Pauli principleexclusion principlePauli's exclusion principle
When combined with the spin-statistics theorem, the spin of electrons results in the Pauli exclusion principle, which in turn underlies the periodic table of chemical elements.
The Pauli exclusion principle is the quantum mechanical principle which states that two or more identical fermions (particles with half-integer spin) cannot occupy the same quantum state within a quantum system simultaneously.

### Elementary particle

elementary particlesparticleparticles
In quantum mechanics and particle physics, spin is an intrinsic form of angular momentum carried by elementary particles, composite particles (hadrons), and atomic nuclei. Hence the allowed values of s are 0, 1⁄2, 1, 3⁄2, 2, etc. The value of s for an elementary particle depends only on the type of particle, and cannot be altered in any known way (in contrast to the spin direction described below).
And within a molecule, the electron's three degrees of freedom (charge, spin, orbital) can separate via the wavefunction into three quasiparticles (holon, spinon, orbiton).

### Samuel Goudsmit

Samuel Abraham GoudsmitGoudsmitGoudsmtt, Samuel Abraham
In 1925, George Uhlenbeck and Samuel Goudsmit at Leiden University suggested the simple physical interpretation of a particle spinning around its own axis, in the spirit of the old quantum theory of Bohr and Sommerfeld.
Samuel Abraham Goudsmit (July 11, 1902 – December 4, 1978) was a Dutch-American physicist famous for jointly proposing the concept of electron spin with George Eugene Uhlenbeck in 1925.

### Wolfgang Pauli

Pauli Wolfgang Pauli’sPauli, Wolfgang
Wolfgang Pauli in 1924 was the first to propose a doubling of electron states due to a two-valued non-classical "hidden rotation".
The discovery involved spin theory, which is the basis of a theory of the structure of matter.

### Ralph Kronig

Ralph De Laer KronigKronig
Ralph Kronig anticipated the Uhlenbeck-Goudsmit model in discussion with Hendrik Kramers several months earlier in Copenhagen, but did not publish.
He is noted for the discovery of particle spin and for his theory of X-ray absorption spectroscopy.

### Lepton

leptonsantileptondilepton
In particle physics, a lepton is an elementary particle of half-integer spin (spin 1⁄2) that does not undergo strong interactions.

### Angular momentum operator

orbital angular momentumangular momentumquantized
The orbital angular momentum operator is the quantum-mechanical counterpart to the classical angular momentum of orbital revolution and appears when there is periodic structure to its wavefunction as the angle varies.
In the special case of a single particle with no electric charge and no spin, the orbital angular momentum operator can be written in the position basis as:

### Quark

quarksantiquarkantiquarks
For example, a helium atom in the ground state has spin 0 and behaves like a boson, even though the quarks and electrons which make it up are all fermions.
Quarks have various intrinsic properties, including electric charge, mass, color charge, and spin.

### Old quantum theory

quantum theoryBohr–Sommerfeld quantizationBohr-Sommerfeld quantization
In 1925, George Uhlenbeck and Samuel Goudsmit at Leiden University suggested the simple physical interpretation of a particle spinning around its own axis, in the spirit of the old quantum theory of Bohr and Sommerfeld.
The theory would have correctly explained the Zeeman effect, except for the issue of electron spin.

### Bose–Einstein statistics

Bose–Einstein distributionBose–EinsteinBose
In contrast, bosons obey the rules of Bose–Einstein statistics and have no such restriction, so they may "bunch together" even if in identical states.
Such particles have integer values of spin and are named bosons, after the statistics that correctly describe their behaviour.

### Photon

photonslight quantaincident photon
The intrinsic properties of particles, such as charge, mass, and spin, are determined by this gauge symmetry.

### W and Z bosons

Z bosonW bosonW and Z particles
The three particles have a spin of 1.

### Weak interaction

weak forceweakweak nuclear force
An interaction occurs when two particles (typically but not necessarily half-integer spin fermions) exchange integer-spin, force-carrying bosons.

### Fermion

fermionsFermionichalf-integer spin
Those particles with half-integer spins, such as 1⁄2, 3⁄2, 5⁄2, are known as fermions, while those particles with integer spins, such as 0, 1, 2, are known as bosons.
According to the spin-statistics theorem in any reasonable relativistic quantum field theory, particles with integer spin are bosons, while particles with half-integer spin are fermions.

### Spin-½

spin-1/2spin-1⁄21⁄2
Hence the allowed values of s are 0, 1⁄2, 1, 3⁄2, 2, etc. The value of s for an elementary particle depends only on the type of particle, and cannot be altered in any known way (in contrast to the spin direction described below).
In quantum mechanics, spin is an intrinsic property of all elementary particles.

### Higgs boson

Higgs fieldHiggs particleGod particle
In the Standard Model, the Higgs particle is a boson with spin zero, no electric charge and no colour charge.

### Gluon

gluonsgluon fieldAntigluon
The gluon is a vector boson; like the photon, it has a spin of 1.

### Graviton

gravitonsanti-gravitonforce carrier of gravity
The graviton must be a spin-2 boson because the source of gravitation is the stress–energy tensor, a second-order tensor (compared with electromagnetism's spin-1 photon, the source of which is the four-current, a first-order tensor).

### Scalar boson

scalar particlescalarpseudoscalar particle
A scalar boson is a boson whose spin equals zero.

### Electron magnetic moment

electron spinspinelectron magnetic dipole moment
The electron, being a charged elementary particle, possesses a nonzero magnetic moment.
In atomic physics, the electron magnetic moment, or more specifically the electron magnetic dipole moment, is the magnetic moment of an electron caused by its intrinsic properties of spin and electric charge.

### Hadron

hadronshadronichadronic decays
In quantum mechanics and particle physics, spin is an intrinsic form of angular momentum carried by elementary particles, composite particles (hadrons), and atomic nuclei.
Like all subatomic particles, hadrons are assigned quantum numbers corresponding to the representations of the Poincaré group: J PC (m), where J is the spin quantum number, P the intrinsic parity (or P-parity), C the charge conjugation (or C-parity), and m the particle's mass.

### Magnetic field

magnetic fieldsmagneticmagnetic flux density
These magnetic moments can be experimentally observed in several ways, e.g. by the deflection of particles by inhomogeneous magnetic fields in a Stern–Gerlach experiment, or by measuring the magnetic fields generated by the particles themselves.
Magnetic fields are produced by moving electric charges and the intrinsic magnetic moments of elementary particles associated with a fundamental quantum property, their spin.

### Relativistic quantum mechanics

non-relativisticnonrelativisticrelativistic equations
When Paul Dirac derived his relativistic quantum mechanics in 1928, electron spin was an essential part of it.
the spin operator, so they interact with electromagnetic fields.