What is Quark: Definition and 256 Discussions

A quark () is a type of elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei. All commonly observable matter is composed of up quarks, down quarks and electrons. Owing to a phenomenon known as color confinement, quarks are never found in isolation; they can be found only within hadrons, which include baryons (such as protons and neutrons) and mesons, or in quark–gluon plasmas. For this reason, much of what is known about quarks has been drawn from observations of hadrons.
Quarks have various intrinsic properties, including electric charge, mass, color charge, and spin. They are the only elementary particles in the Standard Model of particle physics to experience all four fundamental interactions, also known as fundamental forces (electromagnetism, gravitation, strong interaction, and weak interaction), as well as the only known particles whose electric charges are not integer multiples of the elementary charge.
There are six types, known as flavors, of quarks: up, down, charm, strange, top, and bottom. Up and down quarks have the lowest masses of all quarks. The heavier quarks rapidly change into up and down quarks through a process of particle decay: the transformation from a higher mass state to a lower mass state. Because of this, up and down quarks are generally stable and the most common in the universe, whereas strange, charm, bottom, and top quarks can only be produced in high energy collisions (such as those involving cosmic rays and in particle accelerators). For every quark flavor there is a corresponding type of antiparticle, known as an antiquark, that differs from the quark only in that some of its properties (such as the electric charge) have equal magnitude but opposite sign.
The quark model was independently proposed by physicists Murray Gell-Mann and George Zweig in 1964. Quarks were introduced as parts of an ordering scheme for hadrons, and there was little evidence for their physical existence until deep inelastic scattering experiments at the Stanford Linear Accelerator Center in 1968. Accelerator experiments have provided evidence for all six flavors. The top quark, first observed at Fermilab in 1995, was the last to be discovered.

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  1. M

    A Classifying quarks and leptons using LCTs representation

    Hello everyone, I would like to ask for opinions/expertises about the way of classifying quarks and leptons using linear canonical transformations spin representation as explainedin this link https://en.m.wikipedia.org/wiki/Linear_canonical_transformation Are the statements true ? Please find...
  2. D

    B What kind of energy is needed to create particles such as quarks and electrons?

    Quarks and electrons have clear electric polarity. So, can we assume that an electric source as electromagnetic is needed to create those kinds of particles?
  3. Hatem

    B Vibration Patterns of Strings within Quarks?

    Is it possible to study/observe the virbation patterns of a string within a quark? I understang that String Theory is a theoretical framework, however is it possible to make an observation linking the vibrations of the strings within the quarks to the particles produced? If so, has there even...
  4. TR094

    B How much energy do you need to split up a proton?

    is it even possible to split pu a proton and how much energy would it take to do that? i heard that it requires so much that it would make new a quark.
  5. D

    I Quark Numbers in Quarks-Gluons Plasma: Avogadro's Number

    Why quarks numbers of the three colors where exactly equal in the initial quarks-gluons plasma? Seeing the Avogadro number, even a 10E-20 additional excess in one color should give a lot of free quark tracks in bubble chamber.
  6. E

    A Heavy Quark Propagators in HQET

    I have a confusion about how the heavy quark propagators are constructed in HQET and how the loops (in the included figure) are constructed. A standard sort of introduction and motivation to HQET (as in reviews and texts like Manohar & Wise and M.D Schwartz) is as follows : The momentum of a...
  7. James1238765

    I Evaluating the quark neutrino mixing matrix

    The mixing of the 3 generations of fermions are tabulated into the CKM matrix for quarks: $$ \begin{bmatrix} c_{12}c_{13} & s_{12}c_{13} & s_{13}e^{-i\sigma_{13}} \\ -s_{12}c_{23}-c_{12}s_{23}s_{13}e^{i\sigma_{12}} & c_{12}c_{23}-s_{12}s_{23}s_{13}e^{i\sigma_{13}} & s_{23}c_{13} \\...
  8. Q

    Integration of structure function F2 to calculate quark momentum

    I study particle physics with “Particles and Nuclei” / Povh et al. and “Modern particle physics” / Mark Thomson and I am currently at “Deep-Inelastic scattering”. After introducing several scattering equations, such as Rosenbluth, that all include terms for electric AND magnetic scattering, i.e...
  9. MatthewKM

    I Single Quark at Rest: The Mystery of Dark Matter?

    I find it fascinating that all nucleons are three quark configurations. It is proof that each quark needs two others to remain stable. The hypothesis that early in the big bang there was a uniform foam of quarks and coalescence of threes formed protons begs the question: what percentage of...
  10. ohwilleke

    A What New Experiments, If Any, Would Help Determine Light Quark Masses?

    The experimentally measured properties of protons and neutrons are known with exquisite detail. Our data is not quite as extremely precise, but still very good more other baryons and mesons with light quarks (u, d, and s) as valence quarks, such as pions and kaons. Yet, on a percentage basis...
  11. Auxirius

    I What would a hypothetical quark-quark collision yield?

    As seen in the summary, my question is purely hypothetical and I understand that it would most likely be impossible to happen (or I just haven't read enough). The concept that quarks and leptons are the fundamental particles of the universe has existed for a while now - therefore we know that...
  12. Dhananjay

    I Which machine learning model is best for detecting bottom quarks?

    which machine learning model to use to detect bottom quark, and on what basis the segregation should be done
  13. DaniV

    The 1-loop anomalous dimension of massless quark field

    I tried as first step to find Z_q the renormalization parameter, to do so I did the same procedure to find the renormalization parameter of the gauge field of the gluon A^a_\mu when a is representation index a \in {1,2,...,N^2-1} such that A^{a{(R)}}_{\mu}=\frac{1}{\sqrt{Z_A}}A^{a}_{\mu}...
  14. daisey

    I Down Quark: Composed of Up Quark and Electron?

    I have no formal Physics training, just what I've read over time. And I've always read and understood that Quarks are Elementary Particles. I was reading on the web today where someone who seemed to know what he was talking about stated that Down Quarks are not really elementary particles, but...
  15. S

    I What does a quark content that is divided by a square root-mean?

    I was looking at the Wikipedia article on mesons, which has a table of all the observed particles in which one of the columns is the quark content. For most particles, it is a simple set of 2 quarks, but sometimes is shows a more complicate formula, including division by the square-root of some...
  16. P

    A Why Can't a Top Quark Decay Into a Charm or Up Quark?

    Hello, I have a very basic question : why a top quark for example cannot decay into a charm or up quark ? The fact is that I don't really understand where the concept of up- and down-type quark come from (except that they have the same charge). Why a up-type quark cannot transform into...
  17. Dale

    I What is the meaning of the mass assigned to an individual quark?

    A hydrogen atom is less massive than the sum of an unbound proton and an unbound electron. If I add energy to the atom the system becomes more massive, and when I add enough then I have an unbound electron and proton, each of which has the usual mass. So the mass of an electron is the unbound...
  18. K

    I Exploring the Quark Stars: Hexaquarks and Proton Decay

    Question: Is it believed a "quark star" exists within all neutron stars, or just heavier neutron stars. Do protons actually decay under this pressure (quark soup)? Are Hexaquark bosons able to remain stable beyond the limit of a proton, or would they decay at the same time of a regular...
  19. jk22

    B Exploring the Relationship Between Nucleon Shape and Quark Number

    If a nucleon is let say made of 3 quarks then they rather build a triangle than a tetrahedron, so they are flat ? Why is there not 4 quarks ?
  20. M

    A Why Proton & Neutron Contain 3 Quarks - Not 2 or 4?

    Proton and neutron are made up of three quarks (uud and udd). Why aren't there particles uuu or ddd?
  21. stephen weber

    I What are the degrees of freedom of a quark?

    In computer science we simplify lots of things down to arrays. Tensor equations just show the symmetries between these multidimensional arrays. And any model of a quark in our ordered world must have N degrees of freedom. The term called Degrees of Freedom is simple enough. For example a XYZ...
  22. weningth

    A How to deal with colour indices on spinors

    I want to calculate transition amplitudes in QCD for processes like ##q(k)q^\prime(p)\rightarrow q(k^\prime)q^\prime(p^\prime)##, where ##q,q^\prime## are quarks. However, I am unsure what to do with the colour indices of the quark spinors upon squaring the matrix element. For the sake of...
  23. lelouch_v1

    I Quark Model Families and Masses

    Consider the pseudoscalar and vector meson family, as well as the baryon J = 1/2 family and baryon J = 3/2 family. Within each multiplet, for each particle state write down its complete set of quantum numbers, its mass, and its quark state content. Furthermore, for each multiplet draw the (Y...
  24. JackDixon

    B Beta decay and the down quark.

    I was learning about beta decay, and how a down quark decays into an up quark by emitting a W- boson which then becomes an electron and an electron antineutrino. I have two main questions - Firstly, how can the down quark be considered a fundamental particle, when it can break down to produce...
  25. dextercioby

    A Is the "massless quark" hypothesis ever useful?

    So here it goes. All known theorized quarks are found from scattering experiments to be massive, i.e. have a rest mass. Someone with more knowledge than me told me that assuming (against logic, from my point of view) quarks to be massless, i.e. just like a gas of photons, is theoretically...
  26. T

    B Can a Quark Tunnel Out of a Proton?

    Hi everyone, As far as I know tunelling effect can occur within an atom, a proton can "evade" de nuclei. Can this happen also to a quark inside a proton? Will this quark be alone/will the proton have just 2 quarks? I suppose since you don't had any energy to the system the quark wouldn't create...
  27. M

    B Quark Gluon Plasma In the Presence of Charged Leptons?

    It is my understanding that a state of matter known as quark-gluon plasma has been produced artificially and studied in various labs. How is the presence of varying densities of charged leptons such as electrons thought to influence the behavior of any naturally occurring examples of quark gluon...
  28. M

    B Electron - Up Quark Interactions

    I have some questions about forces acting between electrons (-1 charge) and up quarks (+2/3 charge). I did attempt to make sure its a valid line of questioning by privately asking mfb... & I'll ask all the questions up front so as not to annoy the moderators with my follow up questions. So...
  29. A

    I Top Quark Production in p-p Collisions

    Hi, In a p-p collision, where a we look at u ubar → γ → f fbar, where f is a fermion, what channels are available for f? Is f also allowed to be the top quark? In an analogous process where the γ is replaced for example by the Z0 boson, the book by Kane takes f to be all except the top...
  30. F

    I Quark flavor and color independent?

    Each quark as a flavor charge and a color charge. Are these two properties totally independent of each other? Thanks.
  31. Q

    B Neutral pion quark composition help

    Hi guys, Merry Christmas to you all! I wanted to know whether a neutral pion can be made up of a strange quark and an anti-strange quark. I know that the kaon is the only strange meson and all variations contain an s quark but wouldn't the strangeness be zero in an s quark/anti-s quark pair as...
  32. G

    I Are there quark "shells", just as electrons have shells?

    Historically, quantum mechanics, or wave mechanics, arose due to the anomaly that accelerating free charges ( electrons ) radiated EM waves. The quantisation theory provided a solution. Quarks also have electric charge, and are moving at relativistic speeds, and bound in the nucleon. As the...
  33. ohwilleke

    B Why is there still disagreement over the b quark's name?

    Some physics papers today describe the b quark as a beauty quark. For example: Others physics papers today refer to b quarks as bottom quarks. For example: The b quark is a particle that was theoretically predicted to exist in 1973 and first observed experimentally in 1977. But, here we...
  34. T

    I Higgs Boson decay to two Quarks Detected

    https://phys.org/news/2018-08-long-sought-higgs-boson.html
  35. J

    A Quark Parton Model: Explaining Inelastic Scattering

    Hi, I've been studying the quark parton model recently and all seems fine at first. However, there's just one thing bugging me right now. So in the quark parton model it is assumed that inelastic lepton-hadron scattering can be explained by elastic lepton-hadron scattering, but how can it...
  36. C

    I Strong force as exchange of mesons, or of quark and antiquark

    The (residual) strong force between nucleons can be desribed as - The exchange of a meson (from a nucleon to the other), as in picture b) - The exchange of a quark and an antiquark: in picture a) one nucleon "gives" a quark and receive an antiquark and it's the opposite for the other I do...
  37. C

    I Does strong force increase or decrease with aligned spins?

    The deuterium exists only with the proton and neutron of aligned spin, which suggests that the residual strong force is greated with aligned spins, i.e. the binding energy is greater if the spins are aligned. On the other hand the mass of ##\Delta^{+}## is greater than the mass of proton ##p##...
  38. jim mcnamara

    I Is Quark Matter Truly Non-Strange?

    This paper: Bob Holdom, Jing Ren, and Chen Zhang. "Quark Matter May Not Be Strange." Physical Review Letters. DOI: 10.1103/PhysRevLett.120.222001 Proposes properties of elements further along the Periodic Table of elements - than the elements we have created so far. I cannot evaluate the...
  39. W

    How to treat quark color pairs mathematically

    I am trying to work through a problem in the textbook "Particle Physics in a Nutshell." However, I am realizing how little I actually understand about working through problems involving quark color pairs. Given in the problem is the meson color singlet 1/\sqrt{3}(r\bar{r}+g\bar{g}+b\bar{b})...
  40. ohwilleke

    I Excited hadrons v. fundamental particles

    Mesons and baryons have both a ground state and excited states involving the same valence quarks but a higher mass (which can in principle be calculated from QCD). Fundamental fermions and bosons, however, do not appear to display this behavior. They have a ground state, and while there are...
  41. Rabia

    Top quark Polarization understanding

    How top quark polarization is zero? If we see the daughters then how can we justifies its polarization
  42. Jezza

    I Quark mixing and energy conservation

    We've recently been looking at the hadronic decays of the W boson. In this one example, we looked at possible decays for the W boson being produced near its resonance peak, meaning the centre of mass energy is sufficient to produce u,d,c,s & b quarks. However, because we're below the mass of...
  43. R

    A Electron charge vs quark charge

    I have been trying to understand some of the basic differences in the fundamental nature of leptons and quarks. One article on this issue compares leptons and quarks as "oranges vs apples" to which I basically agree except for one aspect. How can the charges of the quarks be 1/3 or 2/3 the...
  44. B

    B Quark confinement and the Higgs mechanism

    There is something that perflexed me. First here are the references to my questions: http://www.latticeguy.net/mypubs/pub017.pdf http://bose.res.in/~bossar/chandu.pdf What I'd like to know is the following: Without superstrings. Quark confinement and asymptotic freedom says as you pull the...
  45. F

    Speed and direction of b and anti-b quark

    Homework Statement A Higgs particle of mass M is moving in the z-direction with speed $\Beta_H$c compared to the lab system. It decays to a b-quark ans anti-b quark, each of mass m. What is the speed and direction of the b-quark compared to the lab-system, if the Higgs system, (a) it is emitted...
  46. wolram

    B If Quark stars exist why do Neutron stars become Black holes?

    From Wikipedia: Quark-degenerate matter may occur in the cores of neutron stars, depending on the equations of state of neutron-degenerate matter. It may also occur in hypothetical quark stars, formed by the collapse of objects above the Tolman–Oppenheimer–Volkoff mass limit for...
  47. P

    What Makes Physics So Fascinating? A Personal Perspective

    I enjoy physics to a great degree. That is my personality
  48. H

    I Why is quark charge exactly 1/3 or 2/3 the lepton charge?

    Even with the charge screening effect it is exact. Is there an explanation in the standard model? Can the fact there are 3 families of particles be involved?
  49. T

    I How big was the "particle zoo" prior to quark discovery

    I am trying to sort out a discrepancy I see between historical accounts which suggest that there were "hundreds of strongly interacting particles (hadrons) believed to be fundamental..." (Wikipedia under "particle zoo" among other places), and my actual count of such particles. Specifically...
  50. STAR GIRL

    What is smallest particle in an electron or a quark?

    What is smallest particle in an electron or a quark?
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