Fermions
A fermion is any particle that has odd-half-integer
(1/2, 3/2, ...) intrinsic
angular momentum (spin), measured in units of
.
As a consequence of
this odd-half-integer angular momentum, all fermions obey the Pauli
Exclusion Principle.
The fundamental matter particles (quarks and leptons, as well as most composite particles, such as protons and neutrons) are fermions. Therefore, due to the Pauli Exclusion Principle, these particles cannot co-exist in the same location. This is a very important property of ordinary matter!
For clarification,
spin is the internal angular momentum of a particle, in units of
.
= 1.055 x 10^-34 J s.
Look at the Fermion and
Boson Chart