- Generation (particle physics)
particle physics, a generation is a division of the elementary particles. Between generations, particles differ only by their mass. All interactions and quantum numbers are identical. There are three generations according to the Standard Modelof particle physics.
Each generation is divided into two
leptons and two quarks. The two leptons may be divided into one with electric charge−1 (electron-like) and one neutral (neutrino); the two quarks may be divided 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. For example, the first-generation electron has a mass of only 0.511
MeV/c2, the second-generation muon has a mass of 106 MeV/c2, and the third-generation tau lepton has a mass of 1777 MeV/c2 (almost twice as heavy as a proton).
atoms are made of particles from the first generation. Electrons surround a nucleus made of protons and neutrons, 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. [http://arxiv.org/abs/hep-ph/0607233 A "Muon Mass Tree" with α-quantized Lepton, Quark and Hadron Masses] (Malcolm H. MacGregor)]
Possibility of a fourth generation
Standard Model, 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)Fact|date=April 2007. 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.
Wikimedia Foundation. 2010.
Look at other dictionaries:
Flavour (particle physics) — In particle physics, flavour or flavor (see spelling differences) is a quantum number of elementary particles related to their weak interactions. In the electroweak theory this symmetry is gauged, and flavour changing processes exist. In quantum… … Wikipedia
Desert (particle physics) — In particle physics, the desert refers to a theorized gap in energy scales between the TeV scale and the GUT scale in which no new physics appears. The idea of the desert was motivated by the observation of approximate, order of magnitude, gauge… … Wikipedia
Generation (disambiguation) — Generation or Generations may refer to: * Generation, a level in a family tree; a new set of descendants, a new version (computers, consumer electronics)cience* Electricity generation, the creation of electricity * Generation (particle physics),… … Wikipedia
physics — /fiz iks/, n. (used with a sing. v.) the science that deals with matter, energy, motion, and force. [1580 90; see PHYSIC, ICS] * * * I Science that deals with the structure of matter and the interactions between the fundamental constituents of… … Universalium
Particle accelerator — Atom smasher redirects here. For other uses, see Atom smasher (disambiguation). A 1960s single stage 2 MeV linear Van de Graaff accelerator, here opened for maintenance A particle accelerator is a device that uses electromagnetic fields to… … Wikipedia
PHYSICS — The material presented in this entry emphasizes those contributions which were important in arriving at verified present day scientific results, rather than those that may have appeared important at the time. Unavoidably it will overlap in parts… … Encyclopedia of Judaism
Physics beyond the Standard Model — Beyond the Standard Model Standard Model … Wikipedia
Particle beam weapon — A particle beam weapon uses an ultra high energy beam of atoms or electrons (i.e., a particle beam) to damage a material target by hitting it, and thus disrupting its atomic and molecular structure. A particle beam weapon is a type of directed… … Wikipedia
Automatic calculation of particle interaction or decay — The automatic calculation of particle interaction or decay is part of the computational particle physics branch. It refers to computing tools that help calculating the complex particle interactions as studied in high energy physics, astroparticle … Wikipedia
Technicolor (physics) — Beyond the Standard Model Standard Model … Wikipedia