Fundamental particles
The fundamental particles that make up our
Universe can be divided into two main categories:
(a) hadrons these
particles 'feel' the strong nuclear force
(b) non-hadrons these particles do not
'feel' the strong nuclear force
These two main division are further divided as
follows:
HADRONSMesons: pions, kaons, eta mesons (composed
of two quarks)
Baryons: protons, neutrons, omega, sigma, lambda particles
(composed of three quarks)
NON-HADRONSLeptons: electrons,
muons, tauons, neutrinos
Photons and gravitons
Note: At the present time gravitons are not known to exist.Leptons are
truly fundamental particles and cannot be broken down into smaller particles (as far as we
know!). However hadrons do have an internal structure being composed of true fundamental
particles called quarks.
(See: 16-19/ Nuclear physics/Nuclear
structure/Text/Quarks)Some of the properties of these particles are shown in
the following table.
Particle |
Symbol |
Rest energy (MeV) |
Charge |
Lifetime (s) |
LEPTONS |
|
|
|
|
Electron |
e |
0.511 |
-1 |
stable |
Neutrino |
n |
very small |
0 |
stable |
Muon |
m |
105.7 |
0 |
2.2x10-6 |
HADRONS |
|
|
|
|
Mesons |
|
|
|
|
Pion |
p+ |
139.6 |
+1 |
2.6x10-8 |
|
po |
135.0 |
0 |
0.8x10-16 |
Kaon |
K |
495 |
|
|
Eta |
h |
549 |
|
<10-18 |
Baryons |
|
|
|
|
Proton |
p |
938.3 |
1 |
stable |
Neutron |
n |
939.6 |
0 |
650 (free) |
Lambda |
L |
1116 |
0 |
2.6x10-10 |
Sigma |
S-1 |
1197 |
-1 |
1.6x10-10 |
|
So |
1192 |
0 |
6x10-20 |
Omega |
W |
1672 |
-1 |
0.8x10-10 |
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