Quark components

1. Aug 1, 2004

daveed

how do scientists figure out the quark constituents of particles, and recognize new quarks when they do?

2. Aug 1, 2004

chroot

Staff Emeritus
To see what's inside a proton, you can do what are called "deep inelastic scattering" experiments, which involve smashing an electron into a proton with an enormous amount of energy, and watching where all the resulting bits of matter go. When you analyze the data of many such experiments, you can determine that there are small constituent particles inside the proton, which stay "solid" even while the proton itself is pretty much blasted completely apart.

Here's a good page for some introductory reading on how particle accelerators can be used to probe the structure of matter.

http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/scatsurv.html#c1

- Warren

3. Aug 1, 2004

marlon

Quarks are studied by looking at baryons and mesons while keeping in mind that the colour-quantumnumbers all add up to "white", i.e. neutral. This is called the quark confinement.

Finding quarks experimentally was achieved in accelerator-experiments by looking at collisions and keeping in mind the energy conservation and momentum conservation. When you detect for example two particles after the collision and measure their momentum, it has to have the same value of the totel momentum before the collision. If this law is not obeyed, then extra new particles have to be introduced with momentumvalues that deliver the extra momentumquantity needed for the conservation law...

quarks were developed theoretically by the mathematical grouptheory applied in QFT. The socalled eightfold way.

regards marlon

4. Aug 2, 2004

daveed

i understand that single quarks have never been observed, anywhere. so how do they predict the masses, since the sum of the quarks masses dont add up to the particle's?

5. Aug 2, 2004

chroot

Staff Emeritus
Free single quarks are theorized to be impossible. The binding energy of a pair of quarks is larger than the rest mass-energy of the quarks themselves. To pull them apart, you have to put it in enough energy to make new quarks. Thus, you never get isolated quarks.

The masses are currently very difficult to work out, but the only way I know of is to study a wide variety of hadrons (particles composed of quarks) of different quark composition and compare their characteristics.

- Warren

6. Aug 2, 2004

marlon

True story, besides keep in mind that this quantity called quark-mass does also alter when looked at in certain specific conditions. To exemplify : the mass of a quark-anti-quark-pair can change when this pair is put in the QCD-vacuum filled with monopole-condensates. i am talking about the dual vacuum here where the roles of magnetic and electric fields have been interchanged. The effective quarkmass depends on the quarkmomentum when we calcutate this quantity in euclidian field-theory. This mass really represents the "classical" correlationfunctoe between the two quarks. This means that the interaction between them two quarks can change depending on its speed. When the interaction changes due to a certain vacuum-background, so will the mass.

Offcourse when we are talking about restmass, which was the original idea I think. Then the vision of Warren is correct. Three quarks with certain restmass do not sum up to the total protonmass because there is binding-energy between the quarks (whatch it, as i stated before : it is this binding-energy that can alter depending on the vacuum-interactions of quarks). This binding-energy is taken into account to deliver the remaining necessary mass to constitute the whole proton-mass.

regards
marlon