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Archive Question #0107

What exactly is the nature of a quark?

Our physics expert is on holiday (Australia - now that's nice) but some excellent reading on he nature of quarks can be found at http://helix.nature.com/nsu/000217/000217-5.html and follow it up with http://www.physics.adelaide.edu.au/cssm/physics_links.html

Greg

Austria actualy, but very nice all the same. Quarks are even more fundamental than protons and neutrons. Three quarks go together to make a proton and three (a different mixture) go together to make a neutron. There are 6 types of Quark called Up, Down, Strange, Charm, Bottom, and Top (In order of increasing heaviness) They have one third or two thirds the charge of an electron and are NEVER seen alone - always as triplets or pairs. Each quark can be one of three colours (they are not actually coloured - its just another name for a type of charge they can have which comes in threes instead of electrical charge which comes in two types). Each quark has a partner in the world or anti-matter so there are also anti-up, anti-down, anti-strange etc. and these have opposite charge and opposite colour. No real particles ever display 'colour'. and so real particles have to be made-up of three differently couloured quarks (which add-up to white=no colour) or a quark/anti-quark pair of colours for example red/anti-red (which also cancels out the colour and so =white). If you follow the above rules you can create any nuclear particle you like and they all have names. The two most familiar are the proton and neutron but there are lots of others including mesons which are made from quark/antiquark pairs. The best book I have on this theory which is called Quantum Chromo Dynamics is called "The Key to The Universe" by John Gribbin and it is quite outdated now. The latest news is that they have actually proved the existance of the heaviest Quark (Top). It is very heavy (and so hard to make in the accelerators) and very unstable (all the quarks are unstable except the bottom two (up and down)). Top lives for such a short time that it seems not to have long enough to find a partner (and so become an uncoloured particle pair or triplet) and so may the first 'naked' quark to be seen. Electrons, muons and tauons are different from quarks, as are the three neutrinos.

Brian

The Key to the Universe was by Nigel Calder and not John Gribbin as I said Earlier. It was published way back in 1977 but remains on of the easiest books to read on the subject of Quarks that I have come across. It was published by BBC Books and had an ISBN code number of 0 563 17091 3. I don't know if you can still get it.

Brian