A quark is an 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. Due to a phenomenon known as color confinement, quarks are never directly observed or found in isolation; they can be found only within hadrons, such as baryons (of which protons and neutrons are examples), and mesons.For this reason, much of what is known about quarks has been drawn from observations of the hadrons themselves.Quarks have various intrinsic properties, including electric charge, mass, color charge and spin. Quarks 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.
The experimental evidence of the fact that quarks are real, was found at SLAC in the 1970s. Jerome Friedman, Henry Kendall, and Richard Taylor received the Nobel Prize for this discovery in 1990.
http://www.nobelprize.org/nobel_prizes/physics/laureates/1990/
Charm quark was discovered in 1974 by Burton Richter and Samuel Ting in 1974. They also got the Nobel prize in 1974.
http://www.nobelprize.org/nobel_prizes/physics/laureates/1976/
Top quark was discovered in 1995 at Fermilab by CDF and D0 collaborations.
The experimental evidence of the fact that quarks are real, was found at SLAC in the 1970s. Jerome Friedman, Henry Kendall, and Richard Taylor received the Nobel Prize for this discovery in 1990.
http://www.nobelprize.org/nobel_prizes/physics/laureates/1990/
Charm quark was discovered in 1974 by Burton Richter and Samuel Ting in 1974. They also got the Nobel prize in 1974.
http://www.nobelprize.org/nobel_prizes/physics/laureates/1976/
Top quark was discovered in 1995 at Fermilab by CDF and D0 collaborations.
What is meant by detecting quarks, the Higgs or the recent gravitational waves is fundamentally a lifetime of physics research exquisite technology, and advanced computational development combined with hard work, sweat and tears, all based on a subjective belief in the deductive aspects of careful observations, deliberate experiments and rational theory.
As far as I know, no free quarks have been detected experimentally.
The whole thing is just a theory, but a good one, explaining many facts.
The quarks are said to be confined.
If there were free quarks, a cloud chamber with magnetic field could do for charged quarks.
If 'real' means 'directly observable away from any interaction region', quarks are not real. Only, their existence is compatible with all experimental results so far, and the quark model with color confinement is the theory that seems best suited to explain the behaviour of hadronic interactions. In fact, as it is well explained in the famous Landau-Lifshits course, Vol. IV, the uncertainty principle, as corrected by relativistic effect, puts an absolute limit on our capability to follow the individual particles (or fields) inside their interaction region for time intervals which are very short, such as those of hadronic interactions. In this view the question about the 'reality' of quarks loses its meaning, and the interaction is described by looking at initial and final states only (Heisenberg's S-matrix theory)
You mention that "Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutron".
Note that protons and neutrons are not the "most stable" hadrons. They are "the only stable" hadrons. All other hadrons are unstable and quickly decay. The only stable particles in the Standard model and in physical reality making up all existing atoms are the electron, the proton and neutron.
The up and down quarks are the only stable quarks in the quarks lot. They have been discovered at the SLAC facility during non-destructive scattering experiments carried out between 1966 and 1968 with beams of electrons and positrons energetic enough to penetrate protons and neutrons.
No other scatterable particle was ever discovered within protons and neutrons.
Up and down quarks behave point-like in all circumstances just like electrons and positrons.
They are not hypothetical as some believe. Detection of up and down quarks has been repeatedly confirmed:
http://www.slac.stanford.edu/pubs/slacpubs/0500/slac-pub-0650.pdf
The free neutron is not really stable, but decays into a proton, electron and anti neutrino. It is only supposed to be stable in atomic nuclei.The slow decay is due to the weak interaction.
As far as I can see, you only "detect" quarks, though appropriate models, which always have assumptions, in scattering experiments, like those you cite. Ie. partons and the like..I would say as not as hypothetical as some would believe.
Juan
Your are right about the neutron. But the reason for its decay wnen isolated is not yet known. Only hypothesis for the moment. Even protons in some isotopes can be similarly unstable. It is not yet known why. Only hypothesis here again.
During the late 1960's SLAC experiments, the up and down quarks were not detected as partons, because they were detected without being expelled.
For a very short period of time after the SLAC accelerator came online in 1966, they used non-desctructive levels of scattering to explore nucleons without destroying them, which only caused the bullet particles, electrons and positrons, to rebound on the quarks inside protons and neutrons, which allowed studing the deflected trajectories of the rebounding electrons and positrons. That's now they could determine their fractional charges and estimate the possible ranges of mass the each type may have.
These two quarks were not detected through appropriate models as you say, but were physically scattered against, contrary to the other quarks that were detected as partons, after they started using destructive scattering energy levels. The whole set was then hypothesized as making up Quantum Chromodynamics and included in the Standard Model, without making the difference clear.
The detail of up and down quarks characteristics can be found in the CRC Handbook of Chemistry and Physics,
You certainly have access to the papers published at SLAC during this period. You can verify for yourself.
No free quarks have been found, and current theory (conveniently) states that they cannot be found.
That they exist is undeniable, however we cannot be sure they exist in the format that physics has configured.
Having said this we know that the quasi electron has been discovered with 1/3 charge of the electron, so I expect some time in the future they will be able to discover free quarks with 1/3 the the charge of the electron- and then we will be able to determine their true nature.
Andrew
Absolutely true that no free moving isolated up or down quarks have been found, and apparently cannot be.
This does not mean that they have not been physically detected inside nucleons as already explained. It is up to each really interested individual go verify this by accessing on his own the pertaining formal papers that account for their discovery at the SLAC facility in the second part of the 1960's. Why on his own? Because no amount of explaining can make a person change a deep conviction if that person will not verify.
Preponderance of the evidence of the complete set of experiments confirms the physical existence of poiint-like behaving up and down quarks as being the only scatterable inner components of proton and neutron.
The paper I gave a link to previously is one of the papers of the set.
You mention that quasi-electrons with 1/3 electron charge have been discovered (intriguingly evocative of the down quark). Can you refer me to the formal article reporting this experimental discovery?
@ Andre
Herein the reference
de-Picciotto, R., Reznikov, M., Heiblum, M., Umansky, V., Bunin, G., Mahalu, D., Direct Observation of a Fractional Charge Nature 389, 162–164 (1997).
Thanks Andrew for the link.
He is the live link via RG
Article Direct Observation of a Fractional Charge
The physics of the fractional quantum hall effect has in principle nothing to do with quarks.
Juan,
From the physicalistic point of view you are of course right. However, several scientists have pointed out the remarkable coincidence that the celebrated factor three occurs both in the case of quarks and in the fractional Hall effect, hoping to see some mathematical analogies, if possible, on a deeper level. As far as I know nothing has of yet come out of these speculations.
Generally speaking, a physical theory which contains objects which are principally not observable directly can be approved or refused by a physicist. This seems to be a matter of fundamental philosophy of science and a matter of success of the predictions of such a phyiscal theory.
The quark model is basically a model which can explain the variety of hadrons which occur in collision experiments and which have an extreme short halflife. The confinement mechanism is basically a construction of thought which is done in such a way that it can 'explain' why quarks cannot occur as single free objects. The question of wether or not quarks are definitely unobservable as free objects, provided they 'exist' at all, is somewhat contradictory to this confinement mechanism.
Meanwhile even more fundamental particle models are considered, see for example https://en.wikipedia.org/wiki/Preon or my incomplete contribution in this field called "hypotron theory" (up to now preliminary research notes are available only in German, http://kreuzer-dsr.de/kdsr/bulleti/KDSR_HypotronTheory_Flyer.pdf).
A remark concerning neutrons: If a nucleus decays and ejects a neutron does not necessarily mean that this neutron has been contained inside the nucleus for all the time before the decay of the nucleus. For example, it is conceivable that
(1) the nucleus contains anti-neutrons instead of neutrons or anti-neutrons as well as neutrons (assuming that neutrons and anti-neutrons inside the nucleus do not annihilate)
and
(2) that there exists inside the nucleus a (random) reaction anti-neutron + neutrino -> neutron + anti-neutrino
and
(3) that such a (random) reaction causes the decay of the nucleus.
A theory based on theoretically inventions is a contradiction in terms. Quarks are theoretically deduced and they are unproven, remaind the LHC on CERN and costs of 15.000.000.000Euro.
But to explain the internal structures of proton, neutron, baryons and atomic nuclei we hav only the Quark-theory. There is currently no other possibility.
The questions shold be: How certain one can be about the quark-theory? What is the reality?
The current quark theory depends too much on all the hadrons and mesons and does not explain accurately the mass of the proton or neutron- which it needs to do,
Here is an alternate theory which agrees withe quark theory but gives the proton and neutron masses to a far higher accuracy.
Article Harmonic quintessence and the derivation of the charge and m...
I guess what is possible is that there is, like the electron, a fundamental positive quark which happens to be the anti down, all the rest are short lived resonances. Fundamentally this leaves the proton as the most fundamenal stable hadron
Hans
We are not certain about the quark theory as you say, meant to explain all characteristics of the proton or the neutron.
We are certain of only one thing, The non-destructive scattering experiments at SLAC revealed the presence of only 3 scatterable, charged and point-like behaving inner components inside both nucleons. Their fractional charges and approximate masses could also be calculated from study of the deflection trajectories.
That's actually all that experiments have revealed as to the inside structure of nucleons. The rest is theorizing, extrapolation, speculation and the like.
@Andre
Agreed and there are some better models, as with the three anti-down quarks ( (of different colour) inhabiting the proton as above.
Andrew
I am intrigued by your equation (1)
Do you have a theory why dividing you equation by the 8th power of the electron gyromantetic ratio gets you so close to the unit charge?
@Andre
Yes its in the paper by James French cited in the references.
Vitally important question did they find any differences in the the 3 point like components that were present
a). in the proton
b). in the neutron
c) in the neutron compared to the proton
Andrew
I could not find a mention for James French's paper in the Reference section of the copy of your paper posted in this thread.
Luiz
Note QCD has been put in question from the befinning not only from the QFT point of view. Rith and Schäfer clearly state in an article of Scientific American that even after decades of trying, nobody was ever able to formulate QCD's equations to completely account for the experimental results.
K. Rith and A. Schäfer. The Mystery of Nucleon Spin, Scientific American, July 1999, page 60.
This can only means that QCD is defective as a theory and that another approach needs to be found. This puts the omen on QCD, but not on the experimental results, which still need to be properly integrated in a proper theory.
@Andre
Appendix G:
In accordance with particle gauge coupling, where the ratio in deformed space-time is given by (rw/r)8 [12], the term (1 + ε)8 is used to calculate the shift in electron charge [Eqs. (1-2)].
12. Evans N. et al. Hadronization at the Ads wall. Phys. Rev. D 81, 066004 (2010).
How about some feedback on the SLAC
Many thanks
@Manuel Malaver de la Fuente
Thank you. I enjoyed the messages and discussions.
I was in a discussion in astrophysics/cosmology. The discussion moved to the question of quarks. So, a question have emerged: was the quark detected?
Answers from @Juan Weisz and @S. Bartalucci addressed good statements.
Good information from @André Michaud and @Andrew Worsley. I have enjoyed.
Thank you all.
@Haraldo: "... was the quark detected?" means at least "Does 'quarks' exist"? This is indeed the fundamental question in particle physics because the whole particle physics based on this assumed particles.
Three subparticles are observed within the protons. If protons or atomic nuclei are smashed we can observe only a high amount of unstable particles for example different mesons.
I claim that this particles are the fragments of the nuclear matter, protons and neutrons. It is possible to reconstruct the structures of atomic nuclei etc. by using of light mesons and at least of electrons and positrons.
Quarks do not exist. The present state of particle physics is a regrettable belive in theories and a inability of analysis.
Thesis The Reason of a realistic View to Particles and Atomic Nuclei
@Hans: Thank you for your comment. Yes, I have understood the question about the quark existence.
The elementary particle physics has traveled with assumptions to explain some observations. For example, the neutron decay is proton + electron and something else (today, "something else" is called antineutrino, from Italian: neutrino = small neutron). Therefore, an effort was done to detect the "new" elementary particle "identified" from neutron decay. Several experiments were thought to detect that new elementary particle.
The quark idea (or theory) was proposed to explain some phenomena. For now, quark is just a theory.
Astrophysics follows the same path: for explaining some observations new concepts have been proposed (dark matter and dark energy are two examples).
Thank you for the reference. I started to read.
Nevertheless, quarks do not have any colour charges and they possess only integer electric charges, +e or -e. This is a consequence of the study of quarks in real space. Why do particle physicists insist on non-physical things? Supersymmetry does not allow them to reach the obvious truth?..
The initial question is a repetition of the theoretical wishes about 'quarks' and not of facts.
Scientists should fall back on facts and not on wishes.
The facts are all the observed real particles. They are thepuzzle pieces of the particle structures.
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