Generation (particle physics)

	Email		Print
	Bookmark		Link

Generation (particle physics)

In particle physics

Particle physics

Particle physics is a branch of physics that studies the elementary particle constituents of matter and radiation, and the interactions between them....
, a generation is a division of the elementary particle

Elementary particle

In particle physics, an elementary particle or fundamental particle is a wiktionary:particle not known to have substructure; that is, it is not known to be made up of smaller particles....
s. Between generations, particles differ only by their mass

Mass

In physical science, mass refers to the degree of acceleration a body acquires when subject to a force: bodies with greater mass are accelerated less by the same force....
. All interaction

Fundamental interaction

In physics, a fundamental interaction or fundamental force is a process by which elementary particles interact with each other. An interaction is often described as a field , and is mediated by the exchange of gauge bosons between particles....
s and quantum number

Quantum number

Quantum numbers describe values of conserved numbers in the dynamics of the quantum system. They often describe specifically the energies of electrons in atoms, but other possibilities include angular momentum, Spin etc....
s are identical. There are three generations according to the Standard Model

Standard Model

Lepton

Leptons are a family of elementary particles, alongside quarks and gauge bosons . Like quarks, leptons are fermions and are subject to the electromagnetic force, the gravitational force, and weak interaction....
s and two quark

Quark

Quarks are a type of elementary particle and major constituents of matter. They are the only particles in the Standard Model to experience all four fundamental interaction, which are also known as fundamental interactions....
s. The two leptons may be classified into one with electric charge

Electric charge

Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. Electrically charged matter is influenced by, and produces, electromagnetic fields....
-1 (electron-like) and one neutral (neutrino); the two quarks may be classified into one with charge -1/3 (down-type) and one with charge +2/3 (up-type).

Each member of a higher generation has greater mass than the corresponding particle of the previous generation.

Discussion

Ask a question about 'Generation (particle physics)'

Start a new discussion about 'Generation (particle physics)'

Answer questions from other users

Full Discussion Forum

Encyclopedia

In particle physics

Particle physics

Elementary particle

Mass

In physical science, mass refers to the degree of acceleration a body acquires when subject to a force: bodies with greater mass are accelerated less by the same force....
. All interaction

Fundamental interaction

Quantum number

Standard Model

Lepton

Quark

Electric charge

	First generation	Second generation	Third generation
Lepton Lepton Leptons are a family of elementary particles, alongside quarks and gauge bosons . Like quarks, leptons are fermions and are subject to the electromagnetic force, the gravitational force, and weak interaction....	Electron Electron The electron is a subatomic particle that carries a negative electric charge. It has elementary particle and is believed to be a point particle....	Muon Muon The muon is an elementary particle similar to the electron, with negative electric charge and a spin of . Together with the electron, the tau lepton, and the three neutrinos, it is classified as a lepton....	Tau Tau lepton The tauon is a negatively charged elementary particle with a lifetime of and a mass of . It has an associated antimatter and neutrinos ....
Neutrino Neutrino Neutrinos are elementary particles that travel close to the speed of light, lack an electric charge, are able to pass through ordinary matter almost undisturbed and are thus extremely difficult to detect....	Electron neutrino	Muon neutrino	Tau neutrino
Down-type quark Quark Quarks are a type of elementary particle and major constituents of matter. They are the only particles in the Standard Model to experience all four fundamental interaction, which are also known as fundamental interactions....	Down quark Down quark The down quark is a first-generation quark with a charge of - elementary charge. It is the second-lightest of all the six flavour of quarks, the lightest being the up quark....	Strange quark Strange quark The strange quark is a second-generation quark with a charge of −elementary charge and a strangeness of −1. It is the third-lightest quark after the up quark and down quarks, with a mass of somewhere between 80 and 130 MeV....	Bottom quark Bottom quark The bottom quark is a third-generation quark with a charge of -elementary charge. Although all quarks are described in a similar way by the quantum chromodynamics, the bottom quark's large mass , combined with low values of the CKM matrix elements Vub and Vcb, gives it a distinctive signature that makes it re...
Up-type quark	Up quark Up quark The up quark is a particle described by the Standard Model theory of physics. It is a first-generation quark with a charge of +elementary charge....	Charm quark Charm quark The charm quark is a second-generation quark with an electric charge of + elementary charge. It is the third most massive of the quarks, at about ....	Top quark Top quark The top quark is the third-generation up-type quark with a charge of +elementary charge. It was discovered in 1995 by the Collider Detector at Fermilab and D0 experiment experiments at Fermilab, and is the most massive of known elementary particles....

Each member of a higher generation has greater mass than the corresponding particle of the previous generation. For example, the first-generation electron has a mass of only 0.511 MeV

MEV

MeV and meV are Multiple of the electron volt unit referring to 1,000,000 eV and 0.001 eV, respectively.Mev or MEV may refer to:...
/c², the second-generation muon has a mass of 106 MeV/c², and the third-generation tauon has a mass of 1777 MeV/c² (almost twice as heavy as a proton).

All ordinary atom

Atom

|-! bgcolor=gray | Properties|-||}The atom is a basic unit of matter consisting of a dense, central atomic nucleus surrounded by a electron cloud of electric charge electrons....
s are made of particles from the first generation. Electrons surround a nucleus

Atomic nucleus

The nucleus of an atom is the very dense region, consisting of nucleons , at the center of an atom. Although the size of the nucleus varies considerably according to the mass of the atom, the size of the entire atom is comparatively constant....
made of proton

Proton

The proton is a subatomic particle with an electric charge of +1 elementary charge. It is found in the nucleus of each atom but is also stable by itself and has a second identity as the hydrogen ion, H+....
s and neutron

Neutron

The neutron is a subatomic particle with no net electric charge and a mass slightly larger than that of a proton.Neutrons are usually found in atomic nucleus....
s, which contain up and down quarks. The second and third generations of charged particles do not occur in normal matter and are only seen in extremely high-energy environments. Neutrinos of all generations stream throughout the universe but rarely interact with normal matter.

It is hoped that a comprehensive understanding of the relationship between the generations of the leptons may eventually explain the ratio of masses of the fundamental particles, and shed further light on the nature of mass generally, from a quantum perspective.

Possibility of a fourth generation

Within the Standard Model

Standard Model

The Standard Model of particle physics is a theory of three of the four known fundamental interactions and the elementary particles that take part in these interactions....
, fourth and further generations have been ruled out by theoretical considerations. Some of the arguments against the possibility of a fourth generation are based on the subtle modifications of precision electroweak observables that extra generations would induce; such modifications are strongly disfavored by measurements. Furthermore, a fourth generation with a light neutrino (one with a mass less than about 40 GeV/c²) has been ruled out by measurements of the widths of the Z boson (LEP, CERN

CERN

The European Organization for Nuclear Research , known as CERN , , is the world's largest particle physics laboratory, situated in the northwest suburbs of Geneva on the France-Switzerland border, established in 1954 in science....
). Nonetheless, searches at high-energy colliders for particles from a fourth generation continue, but as yet no evidence has been observed. In such searches, fourth-generation particles are denoted by the same symbols as third-generation ones with an added prime (e.g. b′ and t′). Given the unlikeliness of any such particles being discovered, no other names have been seriously proposed.