particle physics Particle physics or high-energy physics is the study of Elementary particle, fundamental particles and fundamental interaction, forces that constitute matter and radiation. The field also studies combinations of elementary particles up to the s ...

, a boson ( ) is a

subatomic particle In physics, a subatomic particle is a particle smaller than an atom. According to the Standard Model of particle physics, a subatomic particle can be either a composite particle, which is composed of other particles (for example, a baryon, lik ...

whose

spin quantum number In physics and chemistry, the spin quantum number is a quantum number (designated ) that describes the intrinsic angular momentum (or spin angular momentum, or simply ''spin'') of an electron or other particle. It has the same value for all ...

has an

integer An integer is the number zero (0), a positive natural number (1, 2, 3, ...), or the negation of a positive natural number (−1, −2, −3, ...). The negations or additive inverses of the positive natural numbers are referred to as negative in ...

value (0, 1, 2, ...). Bosons form one of the two fundamental classes of subatomic particle, the other being

fermion In particle physics, a fermion is a subatomic particle that follows Fermi–Dirac statistics. Fermions have a half-integer spin (spin 1/2, spin , Spin (physics)#Higher spins, spin , etc.) and obey the Pauli exclusion principle. These particles i ...

s, which have half odd-integer spin (1/2, 3/2, 5/2, ...). Every observed subatomic particle is either a boson or a fermion.

Paul Dirac Paul Adrien Maurice Dirac ( ; 8 August 1902 – 20 October 1984) was an English mathematician and Theoretical physics, theoretical physicist who is considered to be one of the founders of quantum mechanics. Dirac laid the foundations for bot ...

coined the name ''boson'' to commemorate the contribution of

Satyendra Nath Bose Satyendra Nath Bose (; 1 January 1894 – 4 February 1974) was an Indian theoretical physicist and mathematician. He is best known for his work on quantum mechanics in the early 1920s, in developing the foundation for Bose–Einstein statist ...

, an Indian physicist. Some bosons are

elementary particle In particle physics, an elementary particle or fundamental particle is a subatomic particle that is not composed of other particles. The Standard Model presently recognizes seventeen distinct particles—twelve fermions and five bosons. As a c ...

s occupying a special role in particle physics, distinct from the role of fermions (which are sometimes described as the constituents of "ordinary matter"). Certain elementary bosons (e.g.

gluon A gluon ( ) is a type of Massless particle, massless elementary particle that mediates the strong interaction between quarks, acting as the exchange particle for the interaction. Gluons are massless vector bosons, thereby having a Spin (physi ...

s) act as

force carrier In quantum field theory, a force carrier is a type of particle that gives rise to forces between other particles. They serve as the quanta of a particular kind of physical field. Force carriers are also known as messenger particles, intermedia ...

s, which give rise to forces between other particles, while one (the

Higgs boson The Higgs boson, sometimes called the Higgs particle, is an elementary particle in the Standard Model of particle physics produced by the excited state, quantum excitation of the Higgs field, one of the field (physics), fields in particl ...

) contributes to the phenomenon of

mass Mass is an Intrinsic and extrinsic properties, intrinsic property of a physical body, body. It was traditionally believed to be related to the physical quantity, quantity of matter in a body, until the discovery of the atom and particle physi ...

. Other bosons, such as

meson In particle physics, a meson () is a type of hadronic subatomic particle composed of an equal number of quarks and antiquarks, usually one of each, bound together by the strong interaction. Because mesons are composed of quark subparticles, the ...

s, are composite particles made up of smaller constituents. Outside the realm of particle physics, multiple identical composite bosons behave at high densities or low temperatures in a characteristic manner described by

Bose–Einstein statistics In quantum statistics, Bose–Einstein statistics (B–E statistics) describes one of two possible ways in which a collection of non-interacting identical particles may occupy a set of available discrete energy states at thermodynamic equilibri ...

: for example, a gas of

helium-4 Helium-4 () is a stable isotope of the element helium. It is by far the more abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on Earth. Its nucleus is identical to an alpha particle, and consi ...

atoms becomes a

superfluid Superfluidity is the characteristic property of a fluid with zero viscosity which therefore flows without any loss of kinetic energy. When stirred, a superfluid forms vortex, vortices that continue to rotate indefinitely. Superfluidity occurs ...

at temperatures close to absolute zero. Similarly,

superconductivity Superconductivity is a set of physical properties observed in superconductors: materials where Electrical resistance and conductance, electrical resistance vanishes and Magnetic field, magnetic fields are expelled from the material. Unlike an ord ...

arises because some

quasiparticle In condensed matter physics, a quasiparticle is a concept used to describe a collective behavior of a group of particles that can be treated as if they were a single particle. Formally, quasiparticles and collective excitations are closely relate ...

s, such as

Cooper pair In condensed matter physics, a Cooper pair or BCS pair (Bardeen–Cooper–Schrieffer pair) is a pair of electrons (or other fermions) bound together at low temperatures in a certain manner first described in 1956 by American physicist Leon Cooper. ...

s, behave in this characteristic manner.

Name

The name ''boson'' was coined by

to commemorate the contribution of

, an

Indian Indian or Indians may refer to: Associated with India * of or related to India ** Indian people ** Indian diaspora ** Languages of India ** Indian English, a dialect of the English language ** Indian cuisine Associated with indigenous peoples o ...

physicist. When Bose was a reader (later

professor Professor (commonly abbreviated as Prof.) is an Academy, academic rank at university, universities and other tertiary education, post-secondary education and research institutions in most countries. Literally, ''professor'' derives from Latin ...

) at the

University of Dhaka The University of Dhaka (), also known as Dhaka University (DU), is a public university, public research university located in Dhaka, Bangladesh. Established in 1921, it is the oldest active university in the country. The University of Dhaka w ...

Bengal Bengal ( ) is a Historical geography, historical geographical, ethnolinguistic and cultural term referring to a region in the Eastern South Asia, eastern part of the Indian subcontinent at the apex of the Bay of Bengal. The region of Benga ...

(now in

Bangladesh Bangladesh, officially the People's Republic of Bangladesh, is a country in South Asia. It is the List of countries and dependencies by population, eighth-most populous country in the world and among the List of countries and dependencies by ...

), he and

Albert Einstein Albert Einstein (14 March 187918 April 1955) was a German-born theoretical physicist who is best known for developing the theory of relativity. Einstein also made important contributions to quantum mechanics. His mass–energy equivalence f ...

developed the theory characterising such particles, now known as

and Bose–Einstein condensate.

Elementary bosons

All observed elementary particles are either bosons (with integer spin) or fermions (with odd half-integer spin). Whereas the elementary particles that make up ordinary matter (leptons and quarks) are fermions, elementary bosons occupy a special role in particle physics. They act either as

s which give rise to forces between other particles, or in one case give rise to the phenomenon of

. According to the Standard Model of Particle Physics there are five elementary bosons: * One ''scalar boson'' (spin = 0) **

– the particle that contributes to the phenomenon of

via the Higgs mechanism * Four ''vector bosons'' (spin = 1) that act as force carriers. These are the gauge bosons: ** photon – the force carrier of the electromagnetic field **

s (eight different types) – force carriers that mediate the Strong interaction, strong force ** W and Z bosons, neutral weak boson – the force carrier that mediates the weak interaction, weak force ** W and Z bosons, charged weak bosons (two types) – also force carriers that mediate the weak force * A ''second-order tensor boson'' (spin = 2) called the graviton (G) has been hypothesised as the force carrier for Gravitational force, gravity, but so far all attempts to incorporate gravity into the Standard Model have failed.

Composite bosons

Composite particles (such as hadrons, atomic nucleus, nuclei, and atoms) can be bosons or fermions depending on their constituents. Since bosons have integer Spin (physics), spin and fermions half odd-integer spin, any composite particle made up of an ''even'' number of fermions is a boson (e.g., 1/2 + 1/2 + 1/2 + 1/2 = 2 for the three quarks and an electron in a hydrogen atom). Composite bosons include: * All

s of every type * Stable nuclei with even mass numbers such as deuterium,

(the alpha particle), carbon-12, lead-208, and many others. Even and odd atomic nuclei, Even-mass-number nuclides comprise = 60% of all stable nuclides. They are bosons, i.e. they have integer spin, and almost all of them (148 of the 153) are even-proton / even-neutron (EE) nuclides. The EE nuclides necessarily have spin 0 because of pairing. The remaining 5 stable bosonic nuclides are odd-proton / odd-neutron (OO) stable nuclides (see '). The five odd–odd bosonic nuclides are: : : : : : Tantalum-180m, Each of the five has integer, nonzero spin. As Quantum mechanics, quantum particles, the behaviour of multiple indistinguishable bosons at high densities is described by Bose–Einstein statistics. One characteristic which becomes important in superfluidity and other applications of Bose–Einstein condensates is that there is no restriction on the number of bosons that may occupy the same quantum state. As a consequence, when for example a gas of

atoms is cooled to temperatures very close to absolute zero and the kinetic energy of the particles becomes negligible, it condenses into a low-energy state and becomes a

. Other examples in condensed matter systems include Cooper pair, Cooper pairs in superconductors and Exciton, excitons in semiconductors.Monique Combescot and Shiue-Yuan Shiau, "Excitons and Cooper Pairs: Two Composite Bosons in Many-Body Physics", Oxford University Press ().

Quasiparticles

Certain

s are observed to behave as bosons and to follow

, including Cooper pairs, plasmons and phonons.

Explanatory notes

References