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Sub-atomic particles

Protons I get, and neutrons and electrons. Where do all the other sub-atomic particles you hear about fit in?

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( 5 comments — Leave a comment )
miss_next
Jul. 15th, 2010 08:11 pm (UTC)
Often they don't. Many of the more exotic ones you'll hear about are what you might call cyclotron-puke. They're debris caused by smashing things into each other at close to light speed, and they don't last long enough to have any function.

The ones that do have some use are the quarks, but they are so tightly bound inside other particles that they are never found free in the wild or even in the unusual conditions of a particle accelerator. (This has led to some physicists wondering if they have a real existence or whether they're just a convenient mathematical fiction. Frankly, however, at the sub-atomic level, everything is a bit hazy anyway due to quantum effects, so that question may not have any sensible answer.) Quarks are the basic building blocks of protons and neutrons; each is made up of three quarks, but in a slightly different combination. Other larger and more exotic particles are also made from various types of quarks. When quarks were first postulated (by the Nobel prizewinning physicist Murray Gell-Mann), people freaked out because they would have to have a fractional charge. Actually, though, it's only fractional if you take the charge on the proton or the electron as your basic unit, which is the convention in physics. If you took the charge on the quark to be the basic unit, there would be no fractions, a proton would have a charge of +3, and an electron would have a charge of -3. Quarks would then have a charge of plus or minus 1 or 2, rather than some number of thirds.

There are also little blighters called neutrinos which have no charge and barely interact with matter at all. Nobody really knows what the point of them is, but they've been proved to exist, so presumably there is one.
kargicq
Jul. 16th, 2010 05:52 am (UTC)
This is a great answer. If you'd like more detail on anything, especially the neutrino bit, I'd be happy to add to it but I'll be afk for a few days now.
lanciatore
Jul. 16th, 2010 10:44 am (UTC)
"cyclotron-puke" LOL I like that!
foradan
Jul. 16th, 2010 07:39 am (UTC)
There are basically five types of sub-atomic particles:

- Quarks: known as up, down, strange, charm, top and bottom
- Baryons: which are those made of three quarks, including protons and neutrons, and heavier cousins.
- Mesons: made of a quark, anti-quark pair, act a little like bosons.
- Leptons: electrons and neutrinos, and their heavier cousins: muons and tauons, and associated heavy versions of the neutrino, and,
- Bosons: photons etc.

All but the bosons have associated anti-particles. Antimatter is matter made up of these anti-particles instead of the normal versions. Photons are particles of light, and are associated with the electro-magnetic force. There are other bosons associated with the two nuclear forces, and a proposed graviton associated with gravity. The Higgs boson which CERN is trying to find is a boson that gives other particles their mass.

The number of quarks - the number of anti-quarks is generally conserved. Similarly for leptons. Neutrino's are needed to conserve lepton number in beta decay (where a neutron changes into a proton, an electron and an anti-neutrino).
kargicq
Jul. 16th, 2010 09:06 am (UTC)
Also, neutrinos are needed to conserve energy and momentum. People found that some energy was disappearing in beta decay. This is very, very bad as conservation of energy is possibly the most fundamental assumption of physics, so another particle had to be there...
( 5 comments — Leave a comment )