BOSON

In particle physics, 'bosons' are force carrier particles, such as the photon. They may be either elementary or composite. They are distinguished from fermions (matter particles) by their integer spin. Bosons are named after Indian physicist Satyendra Nath Bose.
While most bosons are composite particles, four bosons (the gauge bosons) are elementary particles not known to be composed of other particles. The only other boson in the Standard Model is the Higgs boson, yet to be discovered experimentally.
In contrast to fermions, bosons can occupy the same quantum state. Thus, bosons with the same energy can occupy the same place in space. Therefore bosons are usually related with radiation while fermions are related with matter, although the distinction between the two is not always clear in quantum physics.

Contents

Basic properties

Composite bosons

Examples of bosons

See also

References

Basic properties

All elementary particles and composite particles are either bosons or fermions (depending on their spin). Particles with half-integer spin are designated fermions; particles with integer spin are designated bosons. The spin-statistics theorem identifies the resulting quantum statistics that differentiate fermions and bosons. Due to their integer spin, bosons obey Bose–Einstein statistics, one consequence of which is the Bose–Einstein condensation of particles—in which any number of bosons can share the same quantum state. This allows masers and lasers to operate—all photons in these devices are in the same quantum state. Thus, bosons do not "resist" when placed at the same place. Fermions, being half-integer spin particles, can't occupy the same quantum state - they "resist" being placed close to each other. So, fermions posses "rigidness" and thus sometimes are considered to be "particles of matter".
While fermions obey the Pauli exclusion principle: "''no more than one fermion can occupy a single quantum state,''" there is no such exclusion property for bosons, which can occupy the same quantum state.
The result is that the spectrum of photon gas of certain equilibrium temperature is a Planck spectrum (one example of which is black-body radiation; another is the thermal radiation of the opaque early Universe seen today as microwave background radiation). Operation of lasers, the properties of superfluid helium-4 and recent formation of Bose–Einstein condensates of atoms are all consequences of statistics of bosons.
Interaction of virtual bosons with real fermions are called fundamental interactions, and these result in all forces we know. The bosons involved in these interactions are called gauge bosons—such as the W vector bosons of the weak force, the gluons of the strong force, the photons of the electromagnetic force, and (in quantum gravity) the graviton of the gravitational force.
In large systems, The difference between bosonic and fermionic statistics is only apparent at large densities—when their wave functions overlap. At low densities, both types of statistics are well approximated by Maxwell-Boltzmann statistics, which is described by classical mechanics.

Composite bosons

Particles composed of a number of other particles (such as protons, neutrons or nuclei) can be either fermions or bosons, depending on their total spin. Hence, many nuclei are in fact bosons. So even though the main three massive subatomic particles i.e. the proton, neutron, and electron are all fermions, it is possible for a single element such as helium to have some isotopes that are fermions (e.g. ³He) and other isotopes that are bosons (e.g. ⁴He). (³He is composed of one neutron and two protons [PNP].) Likewise, the deuteron (²H), which is composed of one proton plus one neutron [NP] is a boson, while the triton (³H), which is composed of two neutrons plus one proton [NPN] is a fermion. The deuterium atom composed of three fermions (proton+neutron+electron) is a fermion, while its nucleus [NP] when separated from the electron is a boson.
Composite bosons exhibit bosonic behavior only at distances large compared to their structure size. At a small distance they behave according to properties of their constituent particles. For example, despite the fact that an alpha particle is a boson, at high energy it interacts with another alpha particle not as a boson but as an ensemble of fermions.

Examples of bosons

Main articles: List of particles#Bosons (integer spin)


★ Photons, which mediate the electromagnetic force

★ W and Z bosons, which mediate the weak nuclear force

★ Gluons

★ Higgs bosons

★ Phonons

★ Cooper pairs

See also

★ Bosonic field

★ Bose gas

★ Fermions

★ Identical particles

★ List of particles

★ Parastatistics

★ Tonks-Girardeau gas

★ Standard model

★ Superconductivity

References

★ Sakurai, J.J. (1994). ''Modern Quantum Mechanics'' (Revised Edition), pp 361-363. Addison-Wesley Publishing Company. ISBN 0-201-53929-2.