Particle Physics
The following table is my interpretation of the main families of
known sub-atomic particles.
| Sub-atomic particles
|
|---|
| | Even spin
Bosons | Odd spin
Fermions
|
|---|
| Light | Force carriers
e.g. photon | Leptons
e.g. electron
(experience the
weak nuclear force)
|
|---|
Heavy
(generally) | Hadrons
(experience the
strong nuclear force) | Mesons
Made of two quarks | Baryons
Made of three quarks
e.g. proton, neutron
|
|---|
| | Quarks
|
|---|
The following table gives more detail on members of these
families.
- Mass is given in Gev/c2 , which is a Giga-Electron-Volts
divided by the speed of light squared.
- Electon-Volts is a measure of energy, and is the energy
gained by an electron crossing a potential of one volt.
- 1eV = 1.6 x 10 -19 joules.
- So 1GeV = 1.6 x 10 -10 joules
Mass is measured in terms of energy because they are equivalent
according to Einstein's equation E = mc2.
1GeV is
about the amount of energy required to create a proton,
because the mass of a proton is 0.938GeV/c2 =
1.67 x 10-27 kg.
- Electric charge is given in terms of the charge of a proton, which
is +1. This is equivalent to 1.6 x 10-19 coulombs
- Spin is the internal angular momentum of a particle. It is given by
h/2pi where h is Planck's constant.
This is
6.58*10 -25 GeV s = 1.05*10 -34 J s
Fermions
(Sub-atomic particles which are constituents of matter
with an odd number of half-spin units, i.e. 1/2, 3/2 5/2, ...)
|
|---|
| | Leptons (spin=1/2) | | Quarks (spin = 1/2)
|
| Class | Name | Mass (GeV/c2) | Electric charge | | Name (Flavor) | Approx. Mass (GeV/c2) | Electric charge
|
| I | electron | 0.000511 | -1 | | up | 0.005 | +2/3
|
| electron-neutrino | < 7x10-9 | 0 | | down | 0.01 | -1/3
|
| II | muon | 0.106 | -1 | | strange | 0.2 | -1/3
|
| muon-neutrino | < 0.0003 | 0 | | charmed | 1.5 | +2/3
|
| III | tau | 1.7771 | -1 | | top | 170 | +2/3
|
| tauon-neutrino | < 0.03 | 0 | | bottom | 4.7 | -1/3
|
|
|
|---|
Bosons
(Sub-atomic particles which are force carriers
with an even number of half-spin units, i.e. 0, 1, 2, ...)
|
|---|
| | Unified electroweak force (spin=1) | | Strong/Color force (spin = 1)
|
|---|
| | Name | Mass (GeV/c2) | Electric charge | | Name | Mass (GeV/c2) | Electric charge
|
|---|
| | Photon | 0 | 0 | | Gluon | 0 | 0
|
|---|
| | W - | 80.22 | -1
|
|---|
| | W + | 80.22 | +1 | | Gravity force (spin = 2)
|
|---|
| | Z 0 | 1.187 | 0 | | Graviton | 0 | 0
|
|---|
|
|
|---|
Hadrons
(Sub-atomic particles which are heavy, strongly interacting, and made of quarks)
|
|---|
| | Baryons (qqq) and Antibaryons (q-q-q-)
are made up of three quarks, so have odd spin
|
|---|
| | Name | Mass (GeV/c2) | Electric charge | Quark content | Spin | Lifetime (secs)
|
| | Proton | 0.93828 | +1 | uud | 1/2 | > 1039
|
| | Neutron | 0.93957 | 0 | udd | 1/2 | 898
|
| | lambda | 1.1156 | 0 | uds | 1/2 | 2.6 x 10 -10
|
| | omega | 1.6725 | -1 | sss | 3/2 | 0.8 x 10 -10
|
| | Mesons (qq-)
are made up of a quark and antiquark, so have even spin and are therefore bosons
|
|---|
| | Name | Mass (GeV/c2) | Electric charge | Quark content | Spin | Lifetime (secs)
|
| | Pion | 0.13957 | +1 | ud- | 0 | 2.6x10 -8
|
| | Kaon | 0.49367 | -1 | su- | 0 | 1.2x10 -16
|
| | Rho | 0.770 | +1 | ud- | 1
|
| | D+ | 1.869 | +1 | cd- | 0
|
| | Eta-c | 2.979 | 0 | cc- | 0
|
Subatomic particles
- There are many, but only a very small number are stable, and therefore only these make up the world.
- Unstable subatomic particles are mostly known from high-energy experiments, where they very quickly decay into stable particles.
- Electric charge only comes in whole units (except for quarks)
- Spin come in half-units.
- An antiparticle has the opposite charge, but the same mass and spin, as its pair.
- All matter consists of atoms.
- An atom consists of a nucleus with a number of “orbiting” electrons.
- An atom is about 10 -8cm
- The nucleus is 10 -12cm diameter, so is a ten-thousanth of the size of the whole atom.
- The nucleus of an atom consists of protons and neutrons.
- Electrons are bound to the nucleus by electromagnetic force.
- Protons and neutrons are held together by the “strong nuclear force”.
- The strong nuclear force is carried by pions (originally called mesons).
- When a pion decays, it forms a muon (among other things)
- A muon is the same as an electron, but 206 times heavier.
- A muon is unstable, and decays into electrons in 2 microseconds.
- Neutrinos are another member of the family of light, weakly-interacting particles called leptons.
- Leptons feel the “weak nuclear force”.
- The charged leptons also are subject to the electromagnetic force.
- Quarks have a charge of either one-third or two-thirds of a unit, so can only exist in pairs or triples.
- Six types of quark are known, up/down, strange/charmed and top/bottom.
- Quarks feel the strong nuclear force.
- All matter is made of up/down quarks plus electrons.
- Further levels, as in the diagram, are equivalent to the first, but heavier, and mostly unstable.
Questions:
- Are all bosons force carriers?
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