What is the experimental evidence that suggests the existence of quarks? How were they discovered? I'm going to assume a particle collider is involved, as it tends to be the case with most subatomic discoveries these days.

How are we able to study something so small with any type of instrument? It seems like at some point, we wouldn't be able to build an instrument on the scale required to detect something so small.

(Would be nice if this could be explained in such a way that a College Physics 1 / 2 could understand it.)

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    $\begingroup$ Bjorken scaling in deep-inelastic scattering, the group structure visible in the hadron spectrum, direct measurement on the charges of the heavier quarks, and several other lines of evidence. But they are pretty technical for the most part. By the way, this stuff is mostly from the 1960s and 70s; it's hardly "these days" unless you're taking a pretty long view. $\endgroup$ – dmckee --- ex-moderator kitten Jan 12 '16 at 1:40
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    $\begingroup$ This question is answered here physics.stackexchange.com/q/201990 Quarks were originally introduced for theoretical reasons like atoms in chemistry, rather than discovered experimentally, Nobel prize was awarded in 1990 for their experimental confirmation. A linear accelerator was involved. $\endgroup$ – Conifold Jan 12 '16 at 2:27
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    $\begingroup$ I think the duplicate reference is a wrong one. This question is asking about experimental evidence for quarks, the duplicate asks and is answered about the elementary nature of quarks. I think it should be reopened $\endgroup$ – anna v Jan 13 '16 at 18:37
  • $\begingroup$ @annav: this question has been reopened, were wanting to write an answer for it? $\endgroup$ – Kyle Kanos Jan 14 '16 at 12:41

What is the experimental evidence that suggests the existence of quarks?

It was a great time for experimentalists back in 1960 when the existence of quarks was first suspected.

How were they discovered?

It was called the eightfold way to start with, and it was found that the plethora of resonances discovered in bubble chamber and counter experiments had an amazing symmetry that could be organized according to the representations of SU(3) . As an example here is the baryon octet.

baryon octed

It immediately implied the existence of a substructure to the baryons , in a similar way to the (proton, neutron) SU(2) symmetry as a substructure of the nucleus :two independent vectors, SU(2), three independent vectors SU(3).


The Gell-Mann–Nishijima formula, developed by Murray Gell-Mann and Kazuhiko Nishijima, led to the Eightfold way classification, invented by Gell-Mann, with important independent contributions from Yuval Ne'eman, in 1961. The hadrons were organized into SU(3) representation multiplets, octets and decuplets, of roughly the same mass, due to the strong interactions; and smaller mass differences linked to the flavor quantum numbers, invisible to the strong interactions. The Gell-Mann–Okubo mass formula systematized the quantification of these small mass differences among members of a hadronic multiplet, controlled by the explicit symmetry breaking of SU(3).

The spin-3⁄2 Ω− baryon, a member of the ground-state decuplet, was a crucial prediction of that classification. After it was discovered in an experiment at Brookhaven National Laboratory, Gell-Mann received a Nobel prize in physics for his work on the Eightfold Way, in 1969.

You state

I'm going to assume a particle collider is involved,

Not a collider experiment. The Omega minus was discovered in a K-proton experiment, the K- from the Brookhaven accelerator .

It was the solid evidence of the consistency of the quark model, since it was discovered after its prediction as missing from the symmetry of the decuplet .

baryon decuplet

first omega-

The first Omega- event in the Brookhaven bubble chamber

The theory developed further into SU(3)xSU(2)xU(1) with the strong interaction coming in strongly, and the charm, bottom and top resonances were discovered after the theoretical prediction, the charm with the j/Psi in the SLAC collider in 1974.

Then came the realization that even though QCD would not allow the quarks and gluons to be free, the signature of these particles would come in jets of ordinary protons, pions, kaons etc. as proposed in 1978 by J.Ellis et al.

At present colliders jets are considered the experimental signature of quarks and gluons in the search for new particles and resonances.

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    $\begingroup$ One should probably point out that the $SU(3)$ of the 'eightfold way' is something entirely different from the $SU(3)$ in the standard model gauge group. $\endgroup$ – Toffomat May 23 '19 at 10:35

The quark model not only explained the plethora of new particles (baryons & mesons) discovered throughout the mid 1900's - it also predicted many new particles. Of course, the predictions developed as the theory developed. Those predictions made that were experimentally verified constitute great evidence. See this list of particle discoveries, particularly during and after the 1960's.

My answer is extremely brief, so I hope some more knowledgeable people can give better answers to this.

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No direct observation of quarks is possible.

At least, quarks is great theoretical conception, very useful in the time of discovery of particles. Probably, now, when we have Particle Zoo well populated, we could revise some initial ideas. There is a time to predict and there is a time to explain collected data and we have many.

But the Quark Model definitely works. That is more than enough from the model as all models in science are temporary.

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