The weak interaction (often called the weak force or sometimes the weak nuclear force) is one of the four fundamental interactions of nature. In the Standard Model of particle physics, it is due to the exchange of the heavy W and Z bosons. Its most familiar effect is beta decay (of neutrons in atomic nuclei) and the associated radioactivity. The word "weak" derives from the fact that the field strength is some 10¹³ times less than that of the strong force. A fundamental interaction is a mechanism by which particles interact with each other, and which cannot be explained by another more fundamental interaction. ... The Standard Model of Fundamental Particles and Interactions For the Standard Model in Cryptography, see Standard Model (cryptography). ... Thousands of particles explode from the collision point of two relativistic (100 GeV per nucleon) gold ions in the STAR detector of the Relativistic Heavy Ion Collider. ... In physics, the W and Z bosons are the elementary particles that mediate the weak nuclear force. ... In nuclear physics, beta decay (sometimes called neutron decay) is a type of radioactive decay in which a beta particle (an electron or a positron) is emitted. ... This article or section does not cite its references or sources. ... A semi-accurate depiction of the helium atom. ... Radioactivity may mean: Look up radioactivity in Wiktionary, the free dictionary. ... The strong nuclear force or strong interaction (also called color force or colour force) is a fundamental force of nature which affects only quarks and antiquarks, and is mediated by gluons in a similar fashion to how the electromagnetic force is mediated by photons. ...

Properties

The weak interaction affects all left-handed leptons and quarks. It is the only force affecting neutrinos (except for gravitation, which is negligible on laboratory scales). The weak interaction is unique in a number of respects: A phenomenon is said to be chiral if it is not identical to its mirror image (see Chirality (mathematics)). The spin of a particle may be used to define a handedness for that particle. ... In physics, a particle is a lepton if it has a spin of 1/2 and does not experience the strong nuclear force. ... For other uses of this term, see: Quark (disambiguation) 1974 discovery photograph of a possible charmed baryon, now identified as the Σc++ In particle physics, the quarks are subatomic particles thought to be elemental and indivisible. ... Neutrinos are elementary particles. ... Gravity redirects here. ...

1. It is the only interaction capable of changing flavour.
2. It is the only interaction which violates parity symmetry P (because it only acts on left-handed particles). It is also the only one which violates CP.
3. It is mediated by heavy gauge bosons. This unusual feature is explained in the Standard Model by the Higgs mechanism.

Due to the large mass of the weak interaction's carrier particles (about 90 GeV/c²), their mean life is limited to about 3×10⁻²⁵ seconds by the uncertainty principle. Even at the speed of light this effectively limits the range of the weak interaction to 10⁻¹⁸ meters, about 1000 times smaller than the diameter of an atomic nucleus. Flavour (or flavor) is a quantum number of elementary particles related to their weak interactions. ... In physics, a parity transformation (also called parity inversion) is the simultaneous flip in the sign of all spatial coordinates: A 3×3 matrix representation of P would have determinant equal to –1, and hence cannot reduce to a rotation. ... P-symmetry is simply the spatial symmetry exhibited during a reflection. ... CP-symmetry is a symmetry obtained by a combination of the C-symmetry and the P-symmetry. ... Gauge bosons are bosonic particles which act as carriers of the fundamental forces of Nature. ... The Standard Model of Fundamental Particles and Interactions For the Standard Model in Cryptography, see Standard Model (cryptography). ... The Higgs mechanism or Anderson-Higgs mechanism, originally proposed by the British physicist Peter Higgs based on a suggestion by Philip Anderson, is the mechanism that gives mass to all elementary particles in particle physics. ... Given an assembly of elements, the number of which decreases ultimately to zero, the lifetime (also called the mean lifetime) is a certain number that characterizes the rate of reduction (decay) of the assembly. ... In quantum physics, the Heisenberg uncertainty principle is a mathematical limit on the accuracy with which it is possible to measure everything there is to know about a physical system. ... The speed of light in a vacuum is an important physical constant denoted by the letter c for constant or the Latin word celeritas meaning swiftness. It is the speed of all electromagnetic radiation in a vacuum, not just visible light. ... A semi-accurate depiction of the helium atom. ...

Since the weak interaction is both very weak and very short range, its most noticeable effect is due to its other unique feature: flavour changing. Consider a neutron (quark content udd; one up quark, two down quarks). Although the neutron is heavier than its sister nucleon, the proton (quark content uud), it cannot decay into a proton without changing the flavour of one of its down quarks. Neither the strong interaction nor electromagnetism allow flavour changing, so this must proceed by weak decay. In this process, a down quark in the neutron changes into an up quark by emitting a W boson, which then breaks up into a high-energy electron and an electron antineutrino. Since high-energy electrons are beta radiation, this is called a beta decay. Image File history File links Neutron_decay. ... In the standard model of particle physics the Cabibbo Kobayashi Maskawa matrix (CKM matrix, sometimes earlier called KM matrix) is a unitary matrix which contains information on the strength of flavour changing weak decays. ... This article or section does not cite its references or sources. ... These are the 6 quarks and their most likely decay modes. ... The up quark is a first-generation quark with a charge of +(2/3)e. ... The down quark is a first-generation quark with a charge of -(1/3)e. ... In physics a nucleon is a collective name for two baryons: the neutron and the proton. ... // For alternative meanings see proton (disambiguation). ... Flavour (or flavor) is a quantum number of elementary particles related to their weak interactions. ... The strong interaction or strong force is today understood to represent the interactions between quarks and gluons as detailed by the theory of quantum chromodynamics (QCD). ... Electromagnetism is the force observed as static electricity, and causes the flow of electric charge (electric current) in electrical conductors. ... This article or section does not cite its references or sources. ... In physics, the W and Z bosons are the elementary particles that mediate the weak nuclear force. ... The electron is a fundamental subatomic particle that carries a negative electric charge. ... Neutrinos are elementary particles. ... Beta particles are high-energy electrons emitted by certain types of radioactive nuclei such as potassium-40. ... In nuclear physics, beta decay (sometimes called neutron decay) is a type of radioactive decay in which a beta particle (an electron or a positron) is emitted. ...

Due to the weakness of the weak interaction, weak decays are much slower than strong or electromagnetic decays. For example, an electromagnetically decaying neutral pion has a life of about 10⁻¹⁶ seconds; a weakly decaying charged pion lives about 10⁻⁸ seconds, a hundred million times longer. A free neutron lives about 15 minutes, making it the unstable subatomic particle with the longest known mean life. In particle physics, pion (short for pi meson) is the collective name for three subatomic particles: Ï€0, Ï€+ and π−. Pions are the lightest mesons and play an important role in explaining low-energy properties of the strong nuclear force. ... A subatomic particle is a particle smaller than an atom: it may be elementary or composite. ... Given an assembly of elements, the number of which decreases ultimately to zero, the lifetime (also called the mean lifetime) is a certain number that characterizes the rate of reduction (decay) of the assembly. ...

Interaction types

There are three basic types of weak interaction vertices (up to charge conjugation and crossing symmetry). Two of them involve charged bosons, they are called "charged current interactions." The third type is called "neutral current interaction." In theoretical physics, crossing symmetry is a relation between the S-matrix that describe processes that can be obtained from each other by replacing incoming particles with outgoing antiparticles after taking the analytic continuation. ... Charged current is one of the ways in which subatomic particles can interact by means of the weak force. ... A neutral current is one of the ways in which subatomic particles can interact by means of the weak nuclear force. ...

• A charged lepton ( such as an electron or a muon ) can emit or absorb a W boson and convert into a corresponding neutrino.
• A down-type quark (with charge -1/3) can emit or absorb a W boson and convert into a superposition of up-type quarks. Conversely, an up-type quark can convert into a superposition of down-type quarks. The exact content of this superposition is given by CKM matrix.
• Either a lepton or a quark can emit or absorb a Z boson.

Two charged-current interactions together are responsible for the beta decay phenomenon. The neutral current interaction was first observed in neutrino scattering experiments in 1974 and in collider experiments in 1983. In physics, a particle is a lepton if it has a spin of 1/2 and does not experience the strong nuclear force. ... The electron is a fundamental subatomic particle that carries a negative electric charge. ... The moons shadow, as seen in muons 700m below ground at the Soudan 2 detector. ... In physics, the W and Z bosons are the elementary particles that mediate the weak nuclear force. ... These are the 6 quarks and their most likely decay modes. ... In the standard model of particle physics the Cabibbo Kobayashi Maskawa matrix (CKM matrix, sometimes earlier called KM matrix) is a unitary matrix which contains information on the strength of flavour changing weak decays. ... In physics, the W and Z bosons are the elementary particles that mediate the weak nuclear force. ... In nuclear physics, beta decay (sometimes called neutron decay) is a type of radioactive decay in which a beta particle (an electron or a positron) is emitted. ...

Violation of symmetry

The laws of nature were long thought to remain the same under mirror reflection, the reversal of all spatial axes. The results of an experiment viewed via a mirror were expected to be identical to the results of a mirror-reflected copy of the experimental apparatus. This so-called law of parity conservation was known to be respected by classical gravitation and electromagnetism; it was assumed to be a universal law. However, in the mid-1950's Chen Ning Yang and Tsung-Dao Lee suggested that the weak interaction might violate this law. Chien Shiung Wu and collaborators in 1957 discovered that the weak interaction in fact maximally violates parity, earning Yang and Lee the 1957 Nobel Prize in Physics. A physical law, scientific law, or a law of nature is a scientific generalization based on empirical observations of physical behavior. ... Spheres reflecting the floor and each other. ... Around 300 BC, the Greek mathematician Euclid laid down the rules of what has now come to be called Euclidean geometry, which is the study of the relationships between angles and distances in space. ... In physics, a parity transformation (also called parity inversion) is the simultaneous flip in the sign of all spatial coordinates: A 3×3 matrix representation of P would have determinant equal to –1, and hence cannot reduce to a rotation. ... In physics, a conservation law states that a particular measurable property of an isolated physical system does not change as the system evolves. ... Gravity redirects here. ... Electromagnetism is the force observed as static electricity, and causes the flow of electric charge (electric current) in electrical conductors. ... Dr. Chen Ning Franklin YANG Chen Ning Franklin YANG (楊振寧 pinyin: Yáng Zhènníng) (born September 22, 1922) is a Chinese American physicist, who worked on statistical mechanics and symmetry principles. ... U.S. government photo Tsung-Dao Lee (李政道 Pinyin: Lǐ Zhèngdào) (born November 24, 1926) is a Chinese American physicist who did work on high energy particle physics, symmetry principles, and statistical mechanics. ... Chien-Shiung Wu (吳健雄 Pinyin: Wú Jiànxíong) (May 31, 1912 - February 16, 1997) was a female Chinese American physicist with an expertise in radioactivity. ... Hannes Alfvén (1908–1995) accepting the Nobel Prize for his work on magnetohydrodynamics [1]. List of Nobel Prize laureates in Physics from 1901 to the present day. ...

Although the weak interaction used to be described by Fermi's theory of a contact four-fermion interaction, the discovery of parity violation and renormalization theory suggested a new approach was needed. In 1957, Robert Marshak and George Sudarshan and, somewhat later, Richard Feynman and Murray Gell-Mann proposed a V−A (vector minus axial vector or left-handed) Lagrangian for weak interactions. In this theory, the weak interaction acts only on left-handed particles (and right-handed antiparticles). Since the mirror reflection of a left-handed particle is right-handed, this explains the maximal violation of parity. In physics, Fermis interaction is an old explanation of the weak force, proposed by Enrico Fermi. ... In particle physics, fermions are particles with half-integer spin. ... Figure 1. ... Enchakkal Chandy George Sudarshan (September 16, 1931, Pallam, in Kottayam district of Kerala, India) is a prominent Indian-American physicist, author, and professor at the University of Texas at Austin. ... Richard Phillips Feynman (May 11, 1918 – February 15, 1988; surname pronounced FINE-man; ) was an American physicist known for expanding the theory of quantum electrodynamics, the physics of the superfluidity of supercooled liquid helium, and particle theory. ... Murray Gell-Mann (born September 15, 1929 in Manhattan, New York City, USA) is an American physicist who received the 1969 Nobel Prize in physics for his work on the theory of elementary particles. ... This article is about vectors that have a particular relation to the spatial coordinates. ... In physics and mathematics, a pseudovector (or axial vector) is a quantity that transforms like a vector under a proper rotation, but gains an additional sign flip under an improper rotation (a transformation that can be expressed as an inversion followed by a proper rotation). ... A Lagrangian of a dynamical system, named after Joseph Louis Lagrange, is a function of the dynamical variables and concisely describes the equations of motion of the system. ...

However, this theory allowed a compound symmetry CP to be conserved. CP combines parity P (switching left to right) with charge conjugation C (switching particles with antiparticles). Physicists were again surprised when in 1964, James Cronin and Val Fitch provided clear evidence in kaon decays that CP symmetry could be broken too, winning them the 1980 Nobel Prize in Physics. Unlike parity violation, CP violation is a very small effect. In physics, and specifically particle physics, CP violation is a violation of the postulated CP symmetry of the laws of physics. ... James Watson Cronin (born September 29, 1931) is an American nuclear physicist. ... Val Logsdon Fitch (born March 10, 1923) is an American nuclear physicist. ... In particle physics, Kaons (also called K-mesons and denoted K) are a group of four mesons distinguished by the fact that they carry a quantum number called strangeness. ... Hannes Alfvén (1908–1995) accepting the Nobel Prize for his work on magnetohydrodynamics [1]. List of Nobel Prize laureates in Physics from 1901 to the present day. ...

Electroweak Theory

The Standard Model of particle physics describes the electromagnetic interaction and the weak interaction as two different aspects of a single electroweak interaction, the theory of which was developed around 1968 by Sheldon Glashow, Abdus Salam and Steven Weinberg (see W and Z bosons). They were awarded the 1979 Nobel Prize in Physics for their work. The Standard Model of Fundamental Particles and Interactions For the Standard Model in Cryptography, see Standard Model (cryptography). ... Electromagnetic interaction is a fundamental force of nature and is felt by charged leptons and quarks. ... This article or section does not cite its references or sources. ... Professor Sheldon Lee Glashow (born December 5, 1932) is an American physicist. ... Abdus Salam at Nobel Prize ceremony with the King of Sweden Dr. Abdus Salam (Urdu: پروفیسر ڈاکٹر عبد السلام) (January 29, 1926 at Santokdas, Sahiwal in Punjab – 21 November 1996 in Oxford, England) was a Pakistani theoretical physicist who received the Nobel Prize in Physics in 1979 for his work in electroweak theory which... Steven Weinberg at Harvard University Steven Weinberg (born May 3, 1933) is an American physicist. ... In physics, the W and Z bosons are the elementary particles that mediate the weak nuclear force. ... Hannes Alfvén (1908–1995) accepting the Nobel Prize for his work on magnetohydrodynamics [1]. List of Nobel Prize laureates in Physics from 1901 to the present day. ...

According to the electroweak theory, at very high energies, the universe has four identical massless gauge bosons similar to the photon and a scalar Higgs field. However, at low energies the symmetry of the Higgs field is spontaneously broken by the Higgs mechanism. This symmetry breaking produces three massless Goldstone bosons which are "eaten" by three of the photon-like fields, giving them mass. These three fields become the W and Z bosons of the weak interaction, while the fourth field remains massless and is the photon of electromagnetism. Gauge bosons are bosonic particles which act as carriers of the fundamental forces of Nature. ... The word light is defined here as electromagnetic radiation of any wavelength; thus, X-rays, gamma rays, ultraviolet light, microwaves, radio waves, and visible light are all forms of light. ... Higgs bosons are hypothetical elementary particles predicted to exist by the Standard Model of particle physics. ... Spontaneous symmetry breaking in physics takes place when a system that is symmetric with respect to some symmetry group goes into a vacuum state that is not symmetric. ... The Higgs mechanism or Anderson-Higgs mechanism, originally proposed by the British physicist Peter Higgs based on a suggestion by Philip Anderson, is the mechanism that gives mass to all elementary particles in particle physics. ... In particle and condensed matter physics, Goldstone bosons (also known as Nambu-Goldstone bosons) are bosons that appear in models with spontaneously broken symmetry. ... In physics, the W and Z bosons are the elementary particles that mediate the weak nuclear force. ...

Although this theory has made a number of impressive predictions, including a prediction of the mass of the Z boson before its discovery, the Higgs boson itself has never been observed. Producing Higgs bosons will be a major goal of the Large Hadron Collider being built at CERN. The Higgs boson is a hypothetical massive scalar elementary particle predicted to exist by the Standard Model of particle physics. ... The Large Hadron Collider (LHC) is a particle accelerator and collider located at CERN, near Geneva, Switzerland ( ). Currently under construction, the LHC is scheduled to begin operation (at reduced energies) in November 2007. ... CERN logo The Organisation Européenne pour la Recherche Nucléaire (English: European Organization for Nuclear Research), commonly known as CERN, pronounced (or in French), is the worlds largest particle physics laboratory, situated just west of Geneva on the border between France and Switzerland. ...

References

• Griffiths, David J. (1987). Introduction to Elementary Particles. Wiley, John & Sons, Inc. ISBN 0-471-60386-4. 

• D.A. Bromley (2000). Gauge Theory of Weak Interactions. Springer. ISBN 3-540-67672-4. 

• Gordon L. Kane (1987). Modern Elementary Particle Physics. Perseus Books. ISBN 0-201-11749-5. 

David J. Griffiths is a U.S. physicist and educator. ...

See also

• Formulation of the standard model
• Weakless Universe — the postulate that weak interactions are not anthropically necessary

This is a detailed description of the standard model (SM) of particle physics. ... The Weakless Universe is a hypothetical universe that contains no weak interactions, but is otherwise very similar to our own universe. ... In physics and cosmology, the anthropic principle is an umbrella term for various dissimilar attempts to explain the structure of the universe by way of coincidentally balanced features that are necessary and relevant to the existence on Earth of biochemistry, carbon-based life, and eventually human beings to observe such...

External links

• Citation for 1957 Nobel Prize
• Citation for 1979 Nobel Prize
• Citation for 1980 Nobel Prize

http://www.yourmom.com

http://www.yourmom.com A fundamental interaction is a mechanism by which particles interact with each other, and which cannot be explained by another more fundamental interaction. ... Physics (from the Greek, (phúsis), nature and (phusiké), knowledge of nature) is the science concerned with the discovery and understanding of the fundamental laws which govern matter, energy, space, and time. ... Gravity redirects here. ... Electromagnetism is the force observed as static electricity, and causes the flow of electric charge (electric current) in electrical conductors. ... The strong interaction or strong force is today understood to represent the interactions between quarks and gluons as detailed by the theory of quantum chromodynamics (QCD). ...