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:

HADRONS
Mesons:   pions, kaons, eta mesons (composed of two quarks)
Baryons:   protons, neutrons, omega, sigma, lambda particles (composed of three quarks)

NON-HADRONS
Leptons:   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