Looking Deeper - Quarks
Just when you think you have everything sussed out some awkward so and so comes along and discovers something that that makes you have to think again.
As particle accelerators became more and more powerful there came a point when the electrons had so much energy that heavy particles, hadrons, could actually be created in the collisions.
This is known as "deep inelastic scattering". Inelastic because kinetic energy is being converted into mass as particles and antiparticles are created.
Here are some of the new particles created:
|
Baryons |
Mesons |
||||||||
| Particle | antiproton | antineutron | delta++ | delta- | pi0 | pi+ | pi- | ||
| Mass | 1 | 1 | 1 | 1 | 2/3 | 2/3 | 2/3 | ||
| Charge | -e | 0 | +2e | -e | 0 | +2/3e | -2/3e | ||
99.9% of the mass of the known universe is made up of protons and neutrons. The particles created here perhaps haven't existed before since shortly after the Big Bang!
Are there many fundamental particles after all or perhaps these particles are made up of even smaller building bricks.
Two American physicists, Murray and Gell-Mann, suggested a pattern which suggested that all hadrons were made up of particles which they called quarks. The particles above could be made up using just 4 types of quark with these properties.
| symbol | u | u | d | d |
| name | up | anti-up | down | anti-down |
| mass | 1/3 | 1/3 | 1/3 | 1/3 |
| charge | +2/3e | -2/3e | -1/3e | +1/3e |
Baryons, including protons and neutrons, were made up of 3 quarks while mesons were made up of 2. Here are a few examples:
| Particle | Quarks |
| proton | u u d |
| neutron | u d d |
| delta ++ | u u u |
| pi- | u d |
Two other types of quark have been discovered, charmed c and strange s ( and c and s ) but these quarks are relatively rare.
More about Quarks
Quarks attract each other by exchanging gluons. This boson is the force carrier for the strong nuclear force.
Quarks cannot exist in isolation. If we try to separate two quarks the attractive force between them increases and we have to do an awful lot of work. Eventually this energy is converted into mass as the quarks separate and two new quarks are created.
Quarks have a property which has been called colour.
| red r | green g | blue b |
| anti-red r | anti-green g | anti-blue b |
Only colour combinations are allowed so that the total colour is white e.g.
