Quark
![](http://upload.wikimedia.org/wikipedia/commons/thumb/9/92/Quark_structure_proton.svg/220px-Quark_structure_proton.svg.png)
In physics, a quark (/kwɔrk/, /kwɑːk/ or /kwɑːrk/) is a type of subatomic particle.[1] In technical terms, quarks are elementary fermions which strongly interact due to their color charge.[2] Because of the phenomenon of color confinement, quarks are never found on their own in nature: they are always bound together in composite particles named hadrons.[3] The most common hadrons are the proton and the neutron, which are the components of atomic nuclei.
There are six different types of quarks, known as flavors: up (symbol:
u
), down (
d
), charm (
c
), strange (
s
), top (
t
), and bottom (
b
).[4]
The lightest flavors, the up quark and the down quark, are generally stable and are very common in the universe, as they are the constituents of protons and neutrons. The more massive charm, strange, top and bottom quarks are unstable and rapidly decay; these can only be produced under high energy conditions, such as in particle accelerators and in cosmic rays. For every quark flavor there is a corresponding antiparticle, called antiquark, that differs from the quark only in that some of its properties have the opposite sign.
The quark model was independently proposed by physicists Murray Gell-Mann and George Zweig in 1964.[5] There was little evidence for the theory until 1968, when electron–proton scattering experiments indicated the existence of substructure within the proton resembling three "sphere-like" regions within the proton.[6][7] By 1995, when the top quark was observed at Fermilab, all the six flavors had been observed.
Since quarks are not found in isolation, their properties can only be deduced from experiments on hadrons.[3] An exception to this is the top quark, which decays so rapidly that it does not produce hadrons at all, and instead is observed through the identification of the particles it has decayed into.[8] Furthermore, it has been theorized in some of the Big Bang theories, that in the very beginning, our extremely hot universe may have contained single quarks, including "free" top quarks, in a quark-gluon plasma.
Classification
![](http://upload.wikimedia.org/wikipedia/commons/thumb/0/00/Standard_Model_of_Elementary_Particles.svg/250px-Standard_Model_of_Elementary_Particles.svg.png)
The Standard Model is the theoretical framework describing all the currently known elementary particles, plus the as-yet-unobserved Higgs boson. This model comprises six flavors[note 1] of quarks,[9] named up, down, charm, strange, top and bottom; the top and bottom flavors are also known as truth and beauty, respectively.[3] Any two quarks of the same flavor are identical particles, meaning that all of their properties are the same.
In the Standard Model, particles of matter, including quarks, are classified as fermions, meaning that their spin quantum number (a property related to their intrinsic angular momentum) is half-integer; as a consequence, they are subject to the Pauli exclusion principle, stating that no two fermions of the same flavor can ever simultaneously occupy the same state. This contrasts with particles mediating forces, which are bosons: that is, they have integer spin, and hence the Pauli exclusion principle does not apply to them. Among elementary fermions, quarks differ from leptons (the best-known flavor of which is the electron), in that they, unlike leptons, have a color charge, a property causing them to engage in strong interaction, the force keeping quarks bound together in hadrons.
Elementary fermions are grouped into three generations, each one comprising two leptons and two quarks. The first generation includes up and down quarks, the second includes charm and strange quarks, and the third includes top and bottom quarks. All searches for a fourth generation of quarks and other elementary fermions have failed, and there is strong indirect evidence that there cannot exist more than three generations.[note 2][10] Particles in higher generations generally have greater mass and are less stable, tending to decay into lower-generation, less massive particles by means of weak interaction. Typically, only the first-generation up and down quarks are in common natural occurrence; heavier quarks can only be created in high-energy conditions, such as in cosmic rays, and quickly decay. Most studies conducted on heavier quarks have been performed in artificially created conditions, such as in particle accelerators.
Antiparticles of quarks are called antiquarks, and denoted by a bar over the letter for the quark, such as
u
for an up antiquark. Like antimatter in general, antiquarks have the same mass and spin of their respective quarks, but the electric charge and other charges have the opposite sign.[11]
Having electric charge, flavor, color charge and mass, quarks are the only known elementary particles engaging in all the four fundamental interactions of contemporary physics: respectively, electromagnetism, weak interaction, strong interaction and gravitation. The last is usually irrelevant at subatomic scales, and is not described by the Standard Model.
See the table of properties below for a more complete analysis of the six quark flavors' properties.
History
![](http://upload.wikimedia.org/wikipedia/commons/thumb/8/87/Murray_Gell-Mann.jpg/170px-Murray_Gell-Mann.jpg)
The quark theory was first postulated by physicists Murray Gell-Mann and George Zweig in 1964.[5] At the time of the theory's initial proposal, the "particle zoo" consisted of several leptons and many different hadrons. Gell-Mann and Zweig developed the quark theory to explain the hadrons; they proposed that various combinations of quarks and antiquarks were the components of the hadrons, which were at the time considered to be indivisible.[12]
The Gell-Mann–Zweig model predicted three quarks, which they named up, down and strange. At the time, the pair of physicists ascribed various properties and values to the three new proposed particles, such as electric charge and spin.[13] The initial reaction of the physics community to the proposal was mixed, many having reservations regarding the actual physicality of the quark concept. They believed the quark was merely an abstract concept that could be temporarily used to help explain certain concepts that were not well understood, rather than an actual entity that existed in the way that Gell-Mann and Zweig had envisioned.[12]
In less than a year, extensions to the Gell-Mann–Zweig model were proposed when another duo of physicists, Sheldon Lee Glashow and James Bjorken, predicted the existence of a fourth flavor of quark, which they referred to as charm. The addition was proposed because it expanded the power and self-consistency of the theory: it allowed a better description of the weak interaction (the mechanism that allows quarks to decay); equalized the number of quarks with the number of known leptons; and implied a mass formula that correctly reproduced the masses of the known mesons.[14]
In 1968, deep inelastic scattering experiments at the Stanford Linear Accelerator Center showed that the proton had substructure.[15][6][7] However, whilst the concept of hadron substructure had been proven, there was still apprehension towards the quark model: the substructures became known at the time as partons (a term proposed by Richard Feynman, and supported by some experimental project reports),[16][17] but it "was unfashionable to identify them explicitly with quarks".[18] These partons were later[when?] identified as up and down quarks.[19] Their discovery also validated the existence of the strange quark, because it was necessary to the model Gell-Mann and Zweig had proposed.[20]
In a 1970 paper,[21] Glashow, John Iliopoulos, and Luciano Maiani gave more compelling theoretical arguments for the as-yet undiscovered charm quark.[22] The number of proposed quark flavors grew to the current six in 1973, when Makoto Kobayashi and Toshihide Maskawa noted that the experimental observation of CP violation could be explained if there were another pair of quarks. They named the two additional quarks top and bottom.[13]
It was the observation of the charm quark that finally convinced the physics community of the quark model's correctness.[18] Following a decade without empirical evidence supporting the flavor's existence, it was created and observed almost simultaneously by two teams in November 1974: one at the Stanford Linear Accelerator Center under Samuel Ting and one at Brookhaven National Laboratory under Burton Richter. The two parties had assigned the discovered particle two different names, J and ψ. The particle hence became formally known as the J/ψ meson and it was considered a quark–antiquark pair of the charm flavor that Glashow and Bjorken had predicted, or the charmonium.[12]
In 1977, the bottom quark was observed by Leon Lederman and a team at Fermilab.[5] This indicated that a top quark probably existed, because the bottom quark was without a partner. However, it was not until eighteen years later, in 1995, that the top quark was finally observed. The top quark's discovery was quite significant, because it proved to be significantly more massive than expected, almost as heavy as a gold atom. Reasons for the top quark's extremely large mass remain unclear.[23]
Etymology
Gell-Mann originally named the quark after the sound ducks make.[24] For some time, Gell-Mann was undecided on an actual spelling for the term he intended to coin, until he found the word quark in James Joyce's book Finnegans Wake:
Three quarks for Muster Mark!
Sure he has not got much of a bark
And sure any he has it's all beside the mark.
— James Joyce, Finnegans Wake
Gell-Mann went into further detail regarding the name of the quark in his book, The Quark and the Jaguar: Adventures in the Simple and the Complex:
In 1963, when I assigned the name "quark" to the fundamental constituents of the nucleon, I had the sound first, without the spelling, which could have been "kwork". Then, in one of my occasional perusals of Finnegans Wake, by James Joyce, I came across the word "quark" in the phrase "Three quarks for Muster Mark". Since "quark" (meaning, for one thing, the cry of the gull) was clearly intended to rhyme with "Mark", as well as "bark" and other such words, I had to find an excuse to pronounce it as "kwork". But the book represents the dream of a publican named Humphrey Chimpden Earwicker. Words in the text are typically drawn from several sources at once, like the "portmanteau" words in "Through the Looking-Glass". From time to time, phrases occur in the book that are partially determined by calls for drinks at the bar. I argued, therefore, that perhaps one of the multiple sources of the cry "Three quarks for Muster Mark" might be "Three quarts for Mister Mark", in which case the pronunciation "kwork" would not be totally unjustified. In any case, the number three fitted perfectly the way quarks occur in nature.
— The Quark and the Jaguar: Adventures in the Simple and the Complex [25], in x, x, Murray Gell-Mann
George Zweig, the co-proposer of the theory, preferred the name ace for the particle he had theorized, but Gell-Mann's terminology came to prominence once the quark model had been commonly accepted.[26]
Properties
Hadronization
Various quark flavor combinations result in the formation of composite particles known as hadrons. There are two types of hadrons: baryons, made of three quarks and mesons made of a quark and an antiquark. (These numbers refer to "valence quarks", the quarks determining the charges of the hadron. Hadrons also contain an indeterminate number of virtual pairs of quarks and their respective antiquarks, called "sea quarks" (see below), whose charges cancel each other.)
The building blocks of the atomic nucleus—the proton and the neutron—are baryons.[27]There are a great number of known hadrons, and most of them are differentiated by their quark content and the properties that these constituent quarks confer upon them.[3]
The existence of hadrons with more valence quarks, called exotic hadrons, has been postulated. Several experiments since 2003 have been claimed to reveal a pentaquark, composed by four quarks and an antiquark (
u
u
d
d
s
), but other similar experiments yielded null results. Other examples include tetraquarks (with two quarks and two antiquarks) and dibaryons (with six quarks); some detected particles have been suggested as candidates to being identified as tetraquarks and dibaryons, but these have not be confirmed.
Weak interaction
A quark of one flavor can transform into a quark of a different flavor by the weak interaction. A quark can decay into a lighter quark by emitting a W boson, or can absorb a W boson to turn into a heavier quark. This mechanism causes the radioactive process of beta decay, in which a neutron "splits" into a proton, an electron and an antineutrino. This occurs when one of the down quarks in the neutron (composed by
u
d
d
) decays into an up quark by emitting a
W−
boson, transforming the neutron into a proton (
u
u
d
). The
W−
boson then decays into an electron (
e−
) and an electron antineutrino (
ν
e).[28] A quark can also emit or absorb a Z boson.
As well as being the only interaction capable of causing flavor changes, the weak interaction is the only interaction violating parity symmetry, that is, the only one which would not stay unchanged if left and right were swapped. It exclusively acts on left-handed quarks and leptons, and on right-handed antiquarks and antileptons.
Electric charge
A quark has a fractional electric charge value, either −1/3 or +2/3 (measured in elementary charges); correspondingly, the charge of an antiquark can be either +1/3 or −2/3. The up, charm and top quarks all have charge of +2/3, while the down, strange and bottom quarks have −1/3. The electric charge of a hadron is the sum of the charges of the constituent quarks;[29] the total is always an integer.
The electric charge of quarks is important in the construction of nuclei. The hadron constituents of the atom, the neutron and proton, have charges of 0 and +1 respectively; the neutron is composed of two down quarks and one up quark, and the proton of two up quarks and one down quark. The total electric charge of a nucleus, that is, the number of protons in it, is known as the atomic number, and it is the main difference between atoms of different chemical elements.[30]
Spin
The term spin denotes a intrinsic property of quantum particles, whose direction is an important degree of freedom. Roughly speaking, the spin of a particle is a contribution to its angular momentum that is not due to its motion. It is sometimes visualized as the rotation of an object around its own axis; hence the name spin. However, this description is incorrect, as elementary particles are believed to be point-like and so they cannot rotate around themselves.
Spin is measured in units of h/(2π), where h is the Planck constant. This unit is often denoted by ħ, and called the "reduced Planck constant". The result of a measurement of the component of the spin of a quark along any axis is always either ħ/2 or −ħ/2; for this reason quarks are classified as spin-1/2 particles, which means they are fermions.[31] The component of spin along any given axis—by convention the z axis—is denoted by an up arrow ↑ for the value +1/2 and down arrow ↓ for −1/2, respectively, which follows the symbol for the flavor. For example, an up quark with a positive spin of 1/2 along the z axis is denoted by u↑.[32]
The quark's spin value contributes to the overall spin of the parent hadron, much as quark's electrical charge does to the overall charge of the hadron. Varying combinations of quark spins result in the total spin value that can be assigned to the hadron.[33] For example, the proton and the
Δ+
baryon are both composed of two up quarks and one down quarks: in the
Δ+
their spins are all aligned in the same direction, yielding a total spin of 3/2, whereas in the proton one of them has the opposite direction, giving a total spin of 1/2. However, this view has been recently challenged in quantum chromodynamics by theories that include vacuum polarization and the coupling of quark hadrons to strange quarks in the vacuum.[citation needed][clarification needed]
Color charge
![](http://upload.wikimedia.org/wikipedia/commons/thumb/3/3f/Hadron_colors.png/170px-Hadron_colors.png)
In addition to the electric charge, quarks possess a property called color charge. Despite its name, this is not related to colors of visible light.[34] There are three types of color charge a quark can carry, named blue, green and red; each of them is complemented by an anti-color: antiblue, antigreen and antired, respectively. While a quark can have red, green or blue charge, an antiquark can have antired, antigreen, or antiblue charge.
In quantum chromodynamics, the system of attraction and repulsion between quarks charged with any of the three colors is called strong interaction. A quark charged with one color value will be attracted to an antiquark carrying the corresponding anticolor, while three quarks all charged with different colors will similarly be forced together. In any other case, a force of repulsion will come into effect.[35] Quarks undergo such color interactions via the exchange of quantum field carrier particles known as gluons, a concept which is further discussed below.
The three color types play a role in the process of hadronization, which is is the process of hadron formation out of quarks and gluons. The result of two attracting quarks that form a stable quark–antiquark pair will be color neutrality: a quark with n color charge plus an antiquark of −n color charge will result in a color charge of 0, or "white". The combination of all three color charges will similarly result in the cancelling out of color charge, yielding the same "white" color charge.
These two methods of color neutral hadronization are the same as the two ways in which all hadrons are formed. Hence, all hadrons will be color neutral. A meson, comprised of two particles, is the result of the binding of a quark and antiquark that have opposite color charges, whereas a baryon, containing three particles, arises from the hadronization of three quarks, all charged with different colors.[36]
Mass
There are two different terms used when describing a quark's mass; current quark mass refers to the mass of a quark by itself, while constituent quark mass refers to the current quark mass plus the mass of the gluon particle field surrounding the quark.[37] These two values are typically very different in their relative size, for several reasons.
In a hadron most of the mass comes from the gluons that bind the constituent quarks together, rather than from the individual quarks; the mass of the quarks is almost negligible compared to the mass derived from the gluons' energy. While gluons are inherently massless, they possess energy, and it is this energy that contributes so greatly to the overall mass of the hadron: see "Mass in special relativity". This is demonstrated by a common hadron—the proton. Composed of one
d
and two
u
quarks, the proton has an overall mass of approximately 938 MeV/c2, of which the three valence quarks contribute around 10 MeV/c2, with the remainder coming from the quantum chromodynamics binding energy (QCBE) provided by sea quarks and gluons.[38][39] This makes direct calculations of quark masses based on quantum chromodynamics quite difficult, and often unreliable, as quantum perturbation methods, that were very successful in quantum electrodynamics, now fail most of the time.
Often, mass values can be derived after calculating the difference in mass between two related hadrons that have opposing or complementary quark components. For example, in comparing the proton to the neutron, where the difference between the two particles is one down quark to one up quark, the relative masses and the mass differences can be measured by the difference in the overall mass of the two hadrons.[38]
The masses of most quarks were within predicted ranges at the time of their discovery, with the notable exception of the top quark, which was found to have a mass approximately equal to that of a gold nucleus; significantly heavier than it was expected.[40] Various theories have been offered to explain this very large mass. Common predictions assert that the answer to the abnormality will be found when more is known about the top quark's interaction with the Higgs (boson) field, and how the Higgs boson field adds very heavily to the total mass, and might also bring about the very existence of mass.[23]
Table of quark properties
The following table summarizes the key properties of the six known quarks:
Name | Symbol | Gen. | Mass (MeV/c2) | I | J | Q | S | C | B′ | T | Antiparticle | Antiparticle symbol |
---|---|---|---|---|---|---|---|---|---|---|---|---|
Up | u |
1st | 1.5 to 3.3 | 1/2 | 1/2 | +2/3 | 0 | 0 | 0 | 0 | Antiup | u |
Down | d |
1st | 3.5 to 6.0 | 1/2 | 1/2 | −1/3 | 0 | 0 | 0 | 0 | Antidown | d |
Charm | c |
2nd | 1270+70 −110 |
0 | 1/2 | +2/3 | 0 | +1 | 0 | 0 | Anticharm | c |
Strange | s |
2nd | 104+26 −34 |
0 | 1/2 | −1/3 | −1 | 0 | 0 | 0 | Antistrange | s |
Top | t |
3rd | 171200±2100 | 0 | 1/2 | +2/3 | 0 | 0 | 0 | +1 | Antitop | t |
Bottom | b |
3rd | 4200+170 −70 |
0 | 1/2 | −1/3 | 0 | 0 | −1 | 0 | Antibottom | b |
(Key: Gen. = generation, I = isospin, J = spin, Q = electric charge, S = strangeness, C = charm, B′ = bottomness, T = topness. Notation like 104+26
−34 denotes measurement uncertainty: the value is between 104 + 26 = 130 and 104 − 34 = 70, with 104 being the most likely value.)
Color confinement and gluons
A key phenomenon called color confinement is thought to keep quarks within a hadron. This refers to a quark's inability to escape as a single particle from its parent hadron, thereby rendering impossible the actual observation of a single quark. Color confinement is primarily caused by interactions with the gluon color field and the gluon exchange between quarks.
Color confinement applies to all quarks, except for the case of the top quark where the actual escape mechanism at extremely high energies is still uncertain. Therefore, most of what is known experimentally about quarks has been inferred indirectly from the effects they have on their parent hadron's properties.[42][43] The top quark is an exception because its lifetime is so short that it does not have a chance to hadronize.[8] One method used is to compare two hadrons that have all but one quark in common. The properties of the differing quarks are then inferred from the difference in values between the two hadrons.
Quarks have an inherent relationship with the gluon, which is technically a massless vector gauge boson. Gluons are responsible for the color field, or the strong interaction, that ensures that quarks remain bound in hadrons and causes color confinement, and are the subjects of the quantum chromodynamics research area.[44] Gluons, roughly speaking, carry both a color charge and an anti-color charge, for example red–antiblue.[45][46]
Gluons are constantly exchanged between quarks through a "virtual" emission and re-absorption process. These gluon exchange events between quarks are extremely frequent, occurring approximately 1024 times every second.[47] When a gluon is transferred between one quark and another, a color change occurs in the receiving and emitting quark;[38][48] for example, if a red quark emits a red–antigreen gluon, it becomes green, and if a green quark absorbs it, it becomes red.[49] These constant switches in color within quarks are mediated by the gluons in such a way that a bound hadron will constantly retain a dynamic and ever-changing set of color types that will preserve the force of attraction, therefore forever disallowing quarks to exist in isolation.[50]
The color field carried by the gluon contributes most significantly to a hadron's indivisibility into single quarks, or color confinement. This is demonstrated by the varying strength of the chromodynamic binding force between the constituent quarks of a hadron; as quarks come closer to each other, the chromodynamic binding force actually weakens in a process called asymptotic freedom. However, when they drift further apart, the strength of the bind dramatically increases. The color field becomes stressed by the drifting away of a quark, much as an elastic band is stressed when pulled apart, and a proportionate and necessary multitude of gluons of appropriate color property are created to strengthen the stretched field. In this way, an infinite amount of energy would be required to wrench a quark from its hadronized state.[51] In practice, as soon as enough energy has been spent to distance the quarks, a quark–antiquark pair would be produced so that two hadrons would exist at the end.
These strong interactions are highly non-linear, because gluons can emit gluons and exchange gluons with other gluons. This property has led to a postulate regarding the possible existence of a glueball—a particle that is purely made of gluons—despite previous observations indicating that gluons cannot exist without the 'attached' quarks. However, this would violate the de Broglie quantum mechanism as applied to gluon color fields, because the "pure particles" with no associated 'wave' would then be the only exception to the wave-particle duality, or de Broglie model, which is known to be applicable to all other quantum particles.[clarification needed] The glueball postulate thus amounts to denying the existence of gluon color fields and of the color confinement mechanism discussed above.[52]
Sea quarks
The quarks that contribute to the quantum numbers of the hadrons are called valence quarks. Hadrons also contain virtual quark–antiquark (
q
q
) pairs, known as sea quarks, originating from the gluons' strong interaction field. Such sea quarks are much less stable, and they annihilate each other very quickly within the interior of the hadron. They are thought to be born from the splitting of a gluon, and thus when a sea quark is annihilated, new gluons are produced.[53] There is a constant quantum flux of sea quarks that are born from the vacuum, and this allows for a steady cycle of gluon splits and rebirths. This flux is colloquially known as "the sea".[54]
Notes
- ^ In this context, the term flavor simply refers to different types of particles, and is unrelated with the everyday concept of flavors of food. See Knowing (2005).
- ^ Each generation comprises exactly one flavor of neutrinos, and if there were more than three neutrino flavors, the abundance of helium-4 produced in Big Bang nucleosynthesis would be greater, and the lifetime of the Z boson would be shorter, than what is observed. See Barrow (1994).
References
- ^ "Fundamental Particles". Oxford Physics. Retrieved 2008-06-29.
- ^ "Quark (subatomic particle)". Encyclopedia Britannica. Retrieved 2008-06-29.
- ^ a b c d Q. Ho-Kim, X.-Y. Phạm (1998). Elementary Particles and Their Interactions: Concepts and Phenomena. Springer. pp. p.169. ISBN 3540636676.
{{cite book}}
:|pages=
has extra text (help) - ^ "Quarks". HyperPhysics. Retrieved 2008-06-29.
- ^ a b c B. Carithers, P. Grannis. "Discovery of the Top Quark" (PDF). Retrieved 2008-09-23.
{{cite journal}}
: Cite journal requires|journal=
(help) - ^ a b E. D. Bloom (1969). "High-Energy Inelastic e-p Scattering at 6° and 10°". Physical Review Letters. 23: p.930. doi:10.1103/PhysRevLett.23.930.
{{cite journal}}
:|pages=
has extra text (help) - ^ a b M. Breidenbach (1969). "Observed Behavior of Highly Inelastic Electron-Proton Scattering". Physical Review Letters. 23: p.935. doi:10.1103/PhysRevLett.23.935.
{{cite journal}}
:|pages=
has extra text (help) - ^ a b F. Garberson (2008). Top Quark Mass and Cross Section Results from the Tevatron. Hadron Collider Physics Symposium (HCP2008), Galena, Illinois, USA.
- ^ K. W. Ford (2005). The Quantum World. Harvard University Press. pp. p.169. ISBN 067401832X.
{{cite book}}
:|pages=
has extra text (help) - ^ Barrow, John. "The Singularity and Other Problems". The Origin of the Universe.
{{cite book}}
: Cite has empty unknown parameters:|origdate=
,|origmonth=
, and|month=
(help) - ^ P. Rowlands (2008). Zero to Infinity. World Scientific. pp. p.406. ISBN 9812709142.
{{cite book}}
:|pages=
has extra text (help) - ^ a b c K.W. Staley (2004). The Evidence for the Top Quark. Cambridge University Press. pp. p.15. ISBN 0521827108.
{{cite book}}
:|pages=
has extra text (help) - ^ a b "Funny Quarks". CERN. Retrieved 2008-09-24.
- ^ B. J. Bjorken, S. L. Glashow (1964). "Elementary Particles and SU(4)". Physics Letters. 11: p.255. doi:10.1016/0031-9163(64)90433-0.
{{cite journal}}
:|pages=
has extra text (help) - ^ J.I. Friedman. "The Road to the Nobel Prize". Hue University. Retrieved 2008-09-29.
- ^ Richard P. Feynman, Proceedings of the 3rd Topical Conference on High Energy Collision of Hadrons, Stony Brook, N. Y. (1969)
- ^ CTEQ Collaboration, S. Kretzer et al., "CTEQ6 Parton Distributions with Heavy Quark Mass Effects", Phys. Rev. D69, 114005 (2004).
- ^ a b D. J. Griffiths (1987). Introduction to Elementary Particles. John Wiley & Sons. pp. p.42. ISBN 0-471-60386-4.
{{cite book}}
:|pages=
has extra text (help) - ^ L. M. Lederman, D. Teresi (2006). The God Particle. Mariner Books. pp. p.208. ISBN 0618711686.
{{cite book}}
:|pages=
has extra text (help) - ^ Schombert, James. "Short History of Particles". University of Oregon. Retrieved 5 October.
{{cite web}}
: Check date values in:|accessdate=
(help); Unknown parameter|accessyear=
ignored (|access-date=
suggested) (help) - ^ S. L. Glashow, J. Iliopoulos, L. Maiani (1970). "Weak Interactions with Lepton-Hadron Symmetry". Physical Review D. 2: 1285. doi:10.1103/PhysRevD.2.1285. Retrieved 2008-09-29.
{{cite journal}}
: CS1 maint: multiple names: authors list (link) - ^ D. J. Griffiths (1987). Introduction to Elementary Particles. John Wiley & Sons. pp. p.44. ISBN 0-471-60386-4.
{{cite book}}
:|pages=
has extra text (help) - ^ a b "New Precision Measurement of Top Quark Mass". Brookhaven National Laboratory News. Retrieved 2008-09-24.
- ^ J. Gribbin, M. Gribbin (1997). Richard Feynman: A Life in Science. Penguin Books. pp. p.194. ISBN ISBN 0-452-27631-4.
{{cite book}}
:|pages=
has extra text (help); Check|isbn=
value: invalid character (help) - ^ M. Gell-Mann (1995). The Quark and the Jaguar: Adventures in the Simple and the Complex. Owl Books. pp. p.180. ISBN 978-0805072532.
{{cite book}}
:|pages=
has extra text (help) - ^ Gleick, J. (1992). Richard Feynman and modern physics. Little Brown and Company. p. 390. ISBN 0-316-903167.
- ^ M. Munowitz (2005). Knowing. Oxford University Press (US). pp. p.35. ISBN 0195167376.
{{cite book}}
:|pages=
has extra text (help) - ^ "Weak Interactions". Virtual Visitor Center. Menlo Park, CA: Stanford Linear Accelerator Center. 2008. Retrieved 2008-09-28.
- ^ B. Povh, K. Rith, C. Scholz, F. Zetsche, M. Lavelle (2004). Particles and Nuclei. Springer. ISBN 3540201688. OCLC 53001447.
{{cite book}}
: CS1 maint: multiple names: authors list (link) - ^ W. Demtröder (2002). Atoms, Molecules and Photons: An Introduction to Atomic- Molecular- and Quantum Physics (1st Edition ed.). Springer. pp. 39–42. ISBN 3540206310.
{{cite book}}
:|edition=
has extra text (help) - ^ F. Close (2006). The New Cosmic Onion. CRC Press. pp. p.82. ISBN 1584887982.
{{cite book}}
:|pages=
has extra text (help) - ^ D. Lincoln (2004). Understanding the Universe. World Scientific. pp. p.116. ISBN 9812387056.
{{cite book}}
:|pages=
has extra text (help) - ^ "Quarks". Antonine Education. Retrieved 2008-07-10.
- ^ B. Gal-Or (1983). Cosmology, Physics, and Philosophy. Springer. pp. p.276. ISBN 0387905812.
{{cite book}}
:|pages=
has extra text (help) - ^ J. S. Trefil, G. Walters (2004). The Moment of Creation. Courier Dover Publications. pp. p.112. ISBN 0486438139.
{{cite book}}
:|pages=
has extra text (help) - ^ B. A. Schumm (2004). Deep Down Things. JHU Press. pp. p.131–132. ISBN 080187971X. OCLC 55229065.
{{cite book}}
:|pages=
has extra text (help) - ^ A. Watson (2004). The Quantum Quark. Cambridge University Press. pp. p.286. ISBN 0521829070.
{{cite book}}
:|pages=
has extra text (help) - ^ a b c M. Veltman (2003). Facts and Mysteries in Elementary Particle Physics. World Scientific. pp. p.46. ISBN 981238149X.
{{cite book}}
:|pages=
has extra text (help) - ^ W. Weise, A. M. Green (1984). Quarks and Nuclei. World Scientific. pp. p.65. ISBN 9971966611.
{{cite book}}
:|pages=
has extra text (help) - ^ F. Canelli. "The Top Quark: Worth its Weight in Gold". University of Rochester. Retrieved 2008-10-24.
- ^ C. Amsler et al. (Particle Data Group), PL B667, 1 (2008) (URL: http://pdg.lbl.gov/2008/tables/rpp2008-sum-quarks.pdf)
- ^ T. Wu, W.-Y. Pauchy Hwang (1991). Relativistic quantum mechanics and quantum fields. World Science. pp. p. 321. ISBN 9810206089.
{{cite book}}
:|pages=
has extra text (help) - ^ D. Papenfuss, D. Lüst, W. Schleich (2002). 100 Years Werner Heisenberg: Works and Impact. Wiley-VCH. ISBN 3527403922. OCLC 50694495.
{{cite book}}
: CS1 maint: multiple names: authors list (link) - ^ P. Renton (1988). Electroweak Interactions. Cambridge University Press. p. 332. ISBN 0521366925.
- ^ C. Grupen, G. Cowan, S. D. Eidelman, T. Stroh (2005). Astroparticle Physics. Springer. pp. p.26. ISBN 3540253122.
{{cite book}}
:|pages=
has extra text (help)CS1 maint: multiple names: authors list (link) - ^ J. Bottomley, J. Baez (1996). "Why are there eight gluons and not nine?". Usenet Physics FAQ. Retrieved 2008-09-28.
- ^ J. A. Jungerman (2000). World in Process. SUNY Press. pp. p.107. ISBN 0791447499.
{{cite book}}
:|pages=
has extra text (help) - ^ F. Wilczek, B. Devine (2006). Fantastic Realities. World Scientific. pp. p.85. ISBN 981256649X.
{{cite book}}
:|pages=
has extra text (help) - ^ Feynman, Richard (1985). QED: The Strange Theory of Light and Matter (1st ed. ed.). Princeton University Press. pp. pp. 136–137. ISBN 0-691-08388-6.
{{cite book}}
:|edition=
has extra text (help);|pages=
has extra text (help) - ^ S. Webb (2004). Out of this World. Springer. pp. p.91. ISBN 0387029303.
{{cite book}}
:|pages=
has extra text (help) - ^ T.Yulsman (2002). Origin. CRC Press. p. 55. ISBN 075030765X.
- ^ J. T. V Tran (1996). '96 Electroweak Interactions and Unified Theories. Atlantica Séguier Frontières. pp. p.60. ISBN 2863322052.
{{cite book}}
:|pages=
has extra text (help) - ^ J. Steinberger (2005). Learning about Particles. Springer. pp. p.130. ISBN 3540213295.
{{cite book}}
:|pages=
has extra text (help) - ^ National Research Council (U.S.). Elementary-Particle Physics Panel (1986). Elementary-particle Physics. National Academies Press. p. 62. ISBN 0309035767.
Further reading
- D. J. Griffiths (1987). Introduction to Elementary Particles. John Wiley & Sons. ISBN 0-471-60386-4.
- A. Pickering (1984). Constructing Quarks: A Sociological History of Particle Physics. The University of Chicago Press. ISBN 0-226-66799-5.
- B. Povh (1995). Particles and Nuclei: An Introduction to the Physical Concepts. Springer-Verlag. ISBN 0-387-59439-6.
External links
![](http://upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/30px-Commons-logo.svg.png)
- A Positron Named Priscilla – A description of CERN’s experiment to count the families of quarks.
- An elementary popular introduction
- Quark dance
- The original English word quark and its adaptation to particle physics