In particle physics, preons are postulated "point-like" particles, conceived to be subcomponents of quarks and leptons. Particle physics is a branch of Physics that studies the elementary constituents of Matter and Radiation, and the interactions between them In Physics, a quark (kwɔrk kwɑːk or kwɑːrk is a type of Subatomic particle. Leptons are a family of fundamental Subatomic particles comprising the Electron, the Muon, and the Tauon (or tau particle as well as their The word was coined by Jogesh Pati and Abdus Salam in 1974. Jogesh C Pati (born 1937 in India) is an Indian American theoretical physicist at the University of Maryland College Park, the joint Abdus Salam ( Urdu: محمد عبد السلام) ( January 29, 1926; Jhang Punjab &ndash November 21, Year 1974 ( MCMLXXIV) was a Common year starting on Tuesday (link will display full calendar of the 1974 Gregorian calendar. Interest in preon models peaked in the 1980s but has slowed as some proposed models were ruled out by collider experiments and no model was able to predict a new experimental result. The 1980s was the decade spanning from January 1 1980 to December 31 1989. A collider is a type of a Particle accelerator involving directed beams of particles.
Background: The urge to simplify the Standard Model
Before the Standard Model (SM) was developed in the 1970s (the key elements of the standard model known as quarks were proposed by Gell-Mann and Zweig in 1964), physicists observed hundreds of different kinds of particles in particle accelerators. The Standard Model of Particle physics is a theory that describes three of the four known Fundamental interactions together with the Elementary particles This article is about the Decade 1970-1979 For the Year 1970 see 1970. In Physics, a quark (kwɔrk kwɑːk or kwɑːrk is a type of Subatomic particle. Murray Gell-Mann (born September 15, 1929) is an American Physicist who received the 1969 Nobel Prize in physics for his work George Zweig (born 1937 in Moscow Russia into a Jewish family was originally trained as a Particle physicist under Richard Feynman and later turned his attention Year 1964 ( MCMLXIV) was a Leap year starting on Wednesday (link will display full calendar of the 1964 Gregorian calendar. These were organized into relationships on their physical properties in a largely ad-hoc system of hierarchies, not entirely unlike the way taxonomy grouped animals based on their physical features. Taxonomy is the practice and science of classification The word comes from the Greek, taxis (meaning 'order' 'arrangement' and, nomos Not surprisingly, the huge number of particles was referred to as the "particle zoo". In Particle physics, the term particle zoo is used colloquially to describe a relatively extensive list of the known elementary particles that almost look like hundreds of species
The Standard Model, which is now the prevailing model of particle physics, dramatically simplified this picture by showing that most of the observed particles were mesons, which are combinations of two quarks, or baryons which are combinations of three quarks, plus a handful of other particles. In Particle physics, a meson is a strongly interacting Boson &mdashthat is a Hadron with integer spin. In Physics, a quark (kwɔrk kwɑːk or kwɑːrk is a type of Subatomic particle. Baryons are the family of Subatomic particles with a Baryon number of 1 The particles being seen in the ever-more-powerful accelerators were, according to the theory, typically nothing more than combinations of these quarks.
Within the Standard Model, there are several different types of particles. This is a list of the different types of particles known and hypothesized One of these, the quarks, has six different kinds, of which there are three varieties in each (dubbed "colors", red, green, and blue, giving rise to QCD: quantum chromodynamics). In Physics, a quark (kwɔrk kwɑːk or kwɑːrk is a type of Subatomic particle. In Particle physics, color charge is a property of Quarks and Gluons which are related to their Strong interactions in the context of Quantum Quantum chromodynamics (abbreviated as QCD is a theory of the Strong interaction ( color force a Fundamental force describing the interactions of the Additionally, there are six different types of what are known as leptons. Leptons are a family of fundamental Subatomic particles comprising the Electron, the Muon, and the Tauon (or tau particle as well as their Of these six leptons, there are three charged particles: the electron, muon, and tauon. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J The muon (from the letter mu (μ--used to represent it is an Elementary particle with negative Electric charge and a spin of 1/2 The tau lepton (often called the tau, tau particle, or occasionally the tauon; symbol) is a negatively charged Elementary particle with The neutrinos comprise the other three leptons, and for each neutrino there is a corresponding member from the other set of three leptons. Neutrinos are Elementary particles that travel close to the Speed of light, lack an Electric charge, are able to pass through ordinary matter almost In the Standard Model, there are also the photons, W+, W−, and Z particles, gluons, and a few open spaces left for the graviton and Higgs boson, which have not yet been discovered. In Physics, the photon is the Elementary particle responsible for electromagnetic phenomena The W and Z bosons are the Elementary particles that mediate the Weak force. Gluons ( Glue and the suffix -on) are Elementary particles that cause Quarks to interact and are indirectly responsible for the In Physics, the graviton is a hypothetical Elementary particle, a Boson to be exact that mediates the force of Gravity in the framework The Higgs Boson is a hypothetical massive scalar Elementary particle predicted to exist by the Standard Model of Particle physics Almost all of these particles come in "left-handed" and "right-handed" versions (see chirality). A phenomenon is said to be chiral if it is not identical to its Mirror image (see Chirality)
The Standard Model also has a number of problems which have not been entirely solved. In particular, no successful theory of gravitation based on a particle theory has yet been proposed. Gravitation is a natural Phenomenon by which objects with Mass attract one another Although the Model assumes the existence of a graviton, all attempts to produce a consistent theory based on them have failed. Additionally, mass remains a mystery in the Standard Model. Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object Although the mass of each successive particle follows certain patterns, predictions of the rest mass of most particles can not be made precisely. The Higgs boson is assumed to "solve" this problem, but to date the Higgs mechanism remains unproven.
The Model also has problems predicting the large scale structure of the universe. For instance, the Model generally predicts equal amounts of matter and anti-matter in the universe, something that is observably not the case. In Particle physics and Quantum chemistry, antimatter is the extension of the concept of the Antiparticle to Matter, where antimatter is composed A number of attempts have been made to "fix" this through a variety of mechanisms, but to date none have won widespread support. Likewise, basic adaptations of the Model suggest the presence of proton decay, which has not yet been observed. In Particle physics, proton decay is a hypothetical form of Radioactive decay in which the Proton decays into lighter Subatomic particles
Preon theory is motivated by a desire to replicate the achievements of the periodic table, and the later Standard Model which tamed the "particle zoo", by finding more fundamental answers to the huge number of arbitrary constants present in the Standard Model.
Preon theory is one of several models to have been put forward in an attempt to provide a more fundamental explanation of the results in experimental and theoretical particle physics. The preon model has attracted comparatively little interest to date among the particle physics community.
Theoretical particle physics considerations to research preon theory
Preon research is motivated by the desire to explain already existing facts (retrodiction), which include
- To reduce the large number of particles, many that differ only in charge, to a smaller number of more fundamental particles. Retrodiction (or postdiction, though this should not be confused with the use of the term in criticisms of parapsychological research) is the act of making a For example, the electron and positron are identical except for charge, and preon research is motivated by explaining that electrons and positrons are composed of similar preons with the relevant difference accounting for charge. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J The positrons or antielectron is the Antiparticle or the Antimatter counterpart of the Electron. The hope is to reproduce the reductionist strategy that has worked for the periodic table of elements. Reductionism can either mean (a an approach to understanding the nature of complex things by reducing them to the interactions of their parts or to simpler or more fundamental things The periodic table of the chemical elements is a tabular method of displaying the Chemical elements Although precursors to this table exist its invention is
- The second and third generation fermions are supposedly fundamental, yet they have higher masses than those of the first generation, and the quarks are unstable and decay into their first generation counterparts. In Particle physics, fermions are particles which obey Fermi-Dirac statistics; they are named after Enrico Fermi. Historically, the instability and radioactivity of some chemical elements were explained in terms of isotopes. A chemical element is a type of Atom that is distinguished by its Atomic number; that is by the number of Protons in its nucleus. Isotopes (Greek isos = "equal" tópos = "site place" are any of the different types of atoms ( Nuclides By analogy this suggests a more fundamental structure for at least some fermions. [1]
- To give prediction for parameters that are otherwise unexplained by the Standard Model, such as particle masses, electric charges and color charges, and reduce the number of experimental input parameters required by the standard model. Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction. In Particle physics, color charge is a property of Quarks and Gluons which are related to their Strong interactions in the context of Quantum
- To provide reasons for the very large differences in energy-masses observed in supposedly fundamental particles, from the electron neutrino to the top quark. Neutrinos are Elementary particles that travel close to the Speed of light, lack an Electric charge, are able to pass through ordinary matter almost The top quark is the third- generation up-type Quark with a charge of +(2/3 e.
- To explain the number of generations of fermions. In Particle physics, a generation is a division of the Elementary particles Between generations particles differ only by their Mass.
- To provide alternative explanations for the electro-weak symmetry breaking without invoking a Higgs field, which in turn possibly needs a supersymmetry to correct the theoretical problems involved with the Higgs field. In Particle physics, the electroweak interaction is the unified description of two of the four Fundamental interactions of nature Electromagnetism and the The Higgs Boson is a hypothetical massive scalar Elementary particle predicted to exist by the Standard Model of Particle physics In Particle physics, supersymmetry (often abbreviated SUSY) is a Symmetry that relates elementary particles of one spin to another particle that Supersymmetry itself has theoretical problems.
- To account for neutrino oscillation and mass. Neutrino oscillation is a quantum mechanical phenomenon predicted by Bruno Pontecorvo whereby a Neutrino created with a specific Lepton
- The desire to make new nontrivial predictions, for example, to provide possible cold dark matter candidates, or to predict that the Large Hadron Collider will not observe a Higgs boson or superpartners. In Physics and cosmology, dark matter is hypothetical Matter that does not interact with the electromagnetic force but whose presence can be inferred from The Higgs Boson is a hypothetical massive scalar Elementary particle predicted to exist by the Standard Model of Particle physics In Particle physics, a superpartner is a particle related to a more standard particle by Supersymmetry.
- The desire to reproduce only observed particles, and to prevent prediction within its framework for non-observed particles (which is a theoretical problem with supersymmetry).
History: Pre-quark theories
A number of physicists have attempted to develop a theory of "pre-quarks" (from which the name preon derives) in an effort to justify theoretically the many parts of the Standard Model that are known only through experimental data.
Other names which have been used for these proposed fundamental particles (or particles intermediate between the most fundamental particles and those observed in the Standard Model) include prequarks, subquarks, maons, alphons, quinks, rishons, tweedles, helons, haplons, and Y-particles. Haim Harari is a physicist who made one of the earliest efforts to develop a Preon model to explain the phenomena appearing in the Standard Model (SM of particle Preon is the leading name in the physics community.
Efforts to develop a substructure date at least as far back as 1974 with a paper by Pati and Salam in Physical Review. Year 1974 ( MCMLXXIV) was a Common year starting on Tuesday (link will display full calendar of the 1974 Gregorian calendar. Physical Review (frequently abbreviated as Phys Rev) is one of the oldest and most-respected Scientific journals publishing research on all aspects of Other attempts include a 1977 paper by Terazawa, Chikashige and Akama, similar, but independent 1979 papers by Ne'eman, Harari[2] and Shupe, a 1981 paper by Frizsch and Mandelbaum, a 1992 paper by D'Souza and Kalman, and a 1997 paper by Larson [3]. Also 1977 (album by Ash. Year 1977 ( MCMLXXVII) was a Common year starting on Saturday (link displays Year 1979 ( MCMLXXIX) was a Common year starting on Monday (link displays the 1979 Gregorian calendar) Year 1981 ( MCMLXXXI) was a Common year starting on Thursday (link displays the 1981 Year 1992 ( MCMXCII) was a Leap year starting on Wednesday (link will display full 1992 Gregorian calendar) Year 1997 ( MCMXCVII) was a Common year starting on Wednesday (link will display full 1997 Gregorian calendar None has gained wide acceptance in the physics world.
Each of the preon models identifies a set of far fewer fundamental particles than those of the Standard Model, explains rules governing how those fundamental particles operate, and shows how those proposed particles and rules can explain the Standard Model, often with predicted small discrepancies from the existing model, proposed new particles, and certain phenomena in the standard model that remain unexplained. The Harari Rishon Model illustrates some of the typical efforts in the field.
Many of the Preon models theorize that the apparent imbalance of matter and anti-matter in the universe is in fact illusory, with large quantities of preon level anti-matter confined within more complex structures.
Many preon models either do not account for the Higgs boson or rule it out, and propose that electro-weak symmetry is broken not by a scalar Higgs field but by composite preons. The Higgs Boson is a hypothetical massive scalar Elementary particle predicted to exist by the Standard Model of Particle physics For example, Fredriksson preon theory does not need the Higgs boson, and explains the electro-weak breaking as the rearrangement of preons, rather than a Higgs-mediated field. In fact, Fredriksson preon model predicts that the Higgs boson does not exist. In the above cited paper, Fredricksson acknowledges the mass paradox represents a problem in his accounting for neutrino mass; however, he proposes a specific arrangement of preons in his model, which he calls the X-quark, which his theory suggests could be a stable good cold, dark matter candidate.
When the term "preon" was coined, it was primarily to explain the two families of spin-1/2 fermions: leptons and quarks. More-recent preon models also account for spin-1 bosons, and are still called "preons".
Theoretical objections to preon theories
The mass paradox
Heisenberg's uncertainty principle states that ΔxΔp ≥ ħ/2 and thus anything confined to a box smaller than Δx would have a momentum of uncertainty proportionally greater. In Quantum physics, the Heisenberg uncertainty principle states that locating a particle in a small region of space makes the Momentum of the particle uncertain Some candidate preon models propose particles smaller than the elementary particles they make up, therefore, the momentum of uncertainty Δp should be greater than the particles themselves.
One preon model started as an internal paper at the Collider Detector at Fermilab (CDF) around 1994. Fermi National Accelerator Laboratory ( Fermilab) located in Batavia near Chicago, Illinois, is a U Year 1994 ( MCMXCIV) was a Common year starting on Saturday (link will display full 1994 Gregorian calendar) The paper was written after the occurrence of an unexpected and inexplicable excess of jets with energies above 200 GeV were detected in the 1992—1993 running period. Year 1992 ( MCMXCII) was a Leap year starting on Wednesday (link will display full 1992 Gregorian calendar) Year 1993 ( MCMXCIII) was a Common year starting on Friday (link will display full 1993 Gregorian calendar)
Scattering experiments have shown that quarks and leptons are "pointlike" down to distance scales of less than 10−18 m (or 1/1000 of a proton diameter). Scattering is a general physical process whereby some forms of Radiation, such as Light, Sound or moving particles for example are forced to deviate from The momentum uncertainty of a preon (of whatever mass) confined to a box of this size is about 200 GeV, 50,000 times larger than the rest mass of an up-quark and 400,000 times larger than the rest mass of an electron. In Classical mechanics, momentum ( pl momenta SI unit kg · m/s, or equivalently N · s) is the product Uncertainty is a term used in subtly different ways in a number of fields including Philosophy, Statistics, Economics, Finance, Insurance
Thus, the preon model represents a mass paradox: How could quarks or electrons be made of smaller particles that would have many orders of magnitude greater mass-energies arising from their enormous momenta?
Chirality and the 't Hooft anomaly-matching constraints
Any candidate preon theory must address particle chirality and the 't Hooft anomaly-matching constraints, and would ideally be more parsimonious in theoretical structure than the Standard Model itself. Gerardus 't Hooft (xeːrɑrt ət hoːft (born July 5, 1946, Den Helder) is a professor in Theoretical physics at Utrecht University Parsimony is a 'less is better' concept of frugality economy stinginess or caution in arriving at a hypothesis or course of action
Possible manner of experimental falsification
Often, preon models propose additional unobserved forces or dynamics to account for their proposed preons compose the particle zoo, which may make the theory even more complicated than the Standard Model, or have implications in conflict with observation.
For example, should the LHC observe a Higgs boson, or superpartners, or both, the observation would be in conflict with the predictions of many preon models, which predict the Higgs boson does not exist, or are unable to derive a combination of preons which would give rise to a Higgs Boson.
In contrast, should a Higgs boson not appear in the increasingly constrained circumstances where the leading proponents of the Standard Model predict that it will be found, preon theory would receive a significant theoretical boost, while many competing theories would be falsified.
Preons in popular culture
In the 1948 reprint/redit of his 1930 novel Skylark Three, E. E. Smith postulated a series of 'subelectrons of the first and second type' with the latter being material properties that corresponded to gravitation. The Skylark of Space is one of the earliest novels of Interstellar travel. E E Smith, also Edward Elmer Smith PhD, EE "Doc" Smith, Doc Smith, "Skylark" Smith, and (to family Ted While this may not have been an element of the original novel (the scientific basis of some of the other novels in the series was revised extensively due to the additional eighteen years of scientific development), even the edited publication may be the first, or one of the first, mentions of the possibility that electrons are not elementary particles.
See additional discussion in the article on the Rishon Model. Haim Harari is a physicist who made one of the earliest efforts to develop a Preon model to explain the phenomena appearing in the Standard Model (SM of particle
See also
References
- Pati, J. C.; Salam, A. (1974); Lepton number as the fourth "color", Phys. A preon star is a hypothetical Compact star made of Preons a group of Theoretical Subatomic particles that may compose Quarks Degenerate matter is matter which has sufficiently high Density that the dominant contribution to its Pressure rises from the Pauli Exclusion Haim Harari is a physicist who made one of the earliest efforts to develop a Preon model to explain the phenomena appearing in the Standard Model (SM of particle Jogesh C Pati (born 1937 in India) is an Indian American theoretical physicist at the University of Maryland College Park, the joint Abdus Salam ( Urdu: محمد عبد السلام) ( January 29, 1926; Jhang Punjab &ndash November 21, Rev. D10, 275-289
External links
- Splitting the quark, Nature, 30 November 2007
Dictionary
preon
-noun
- (physics) A hypothetical point-like particle, supposed to be a subcomponent of quarks and leptons.
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