See also: Boson (homonymy)

The bosons represent a class of particles which have particular properties of Symétrie during the exchange of particles: a behaving system of identical particles as bosons is always in a completely symmetrical state with respect to the exchange of particles. All the Elementary particles to date discovered are either of bosons, or of the Fermion S, the latter being able to be only in one completely antisymmetric state with respect to the exchange of particles. The Théorème spin-statistics indicates that the particles of whole Spin are bosons, whereas the particles of spin half-entirety are fermions.

History

The term of boson comes from the name of the physicist Satyendranath Bose and would have been used for the first time by Paul Dirac. Bump carried out the first that to explain the law of Planck describing the radiation of the black body starting from the Photon S previously discovered by Einstein, it had to be supposed that the photons do not follow the Statistique of Maxwell-Boltzmann, but rather statistics from now on called Statistique of Bump-Einstein. Bump writes a short article, Planck' S Law and the Hypothesis off Light Quanta , which it sends to Albert Einstein, after a rejection by the Philosophical Magazine . Einstein is favorably impressed and recommends it for publication in Zeitschrift für Physik , and it does itself of it the translation of the English towards the German . Einstein also will extend the concept of boson to other particles such as the atoms and will contribute to the popularity of the concept of boson.

Exchange identical particles in quantum mechanics

See also: indistinguishable Particles

The fact that in quantum mechanics the particles do not follow a given trajectory makes the identification of the particles completely impossible. In other words, the particles are indistinguables one of the other, and do not have clean individuality. It follows that a measurement supplements on each particle cannot be enough to characterize the state of the system completely, this phenomenon being called degeneration of exchange.

To illustrate what one understands by degeneration of exchange, let us suppose given a complete Ensemble of observable which commutates (ECOC) for a particle and note $\backslash$

Elementary particles behaving like bosons

Among the elementary particles to date discovered, the bosons all are of the bosons of gauge , i.e. they act like intermediaries of the fundamental interactions:

• the Photon is the vector of the electromagnetic interaction

• the eight Gluon S of the strong interaction
• the Z⁰ bosons, W^- and W⁺ of the weak interaction

The standard model of the physics of the particles predicts the existence of two additional particles, the Boson of Higgs, object of many research, but which was not highlighted until now, and the Graviton, boson of gauge which would be responsible for the gravitational interaction.

By studying the properties of birefringence of the vacuum, Italian team PVLAS showed the possible existence of a very light boson, the Axion, of mass 1-1.5 meV. The effect observed can however be explained differently, and other experiments are in hand to confirm or cancel the existence of this particle.

Composite bosons

The particles made up of more elementary particles, such as for example the atoms or the Proton, can be Fermion S or bosons, according to their total Spin (entirety for bosons, half-entirety for the fermions).

Composite examples of bosons:

• atom of helium 4
• state of two electrons forming a pair of Cooper in the superconductive materials
• Exciton
• Polariton

Phenomena showing the behavior bosonic

See also: Statistical of Bump-Einstein

Whereas the fermions obey the Principe of exclusion of Pauli: “ a quantum state given can be occupied only by with the one fermion ”, it is not the case of bosons. A quantum state bosonic can be occupied by an unspecified number of bosons. It is even the reverse which occurs and the bosons tend to gather in a given quantum state.

Consequently, like many cores or atoms are bosons, in certain cases they can accumulate in the same level. This makes it possible to explain:

• the Radiation of the black body, which is explained by the statistics of the photons;
• macroscopic population of a single mode of photon in a Laser ;
• the collapse of the atoms in the state of lower energy at low temperature (condensation of Bump-Einstein), which is at the base of the properties Superfluide S of Helium 4 liquid at low temperature;
• grouping of the photons during their detection (Experiment of Hanbury-Brown and Twiss)

Notes and references of the article

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