Statistics of Particles...
Classification by Spin

Pauli Exclusion Principle: no two particles in the same state (identical spin, color charge, angular momentum, etc.) can exist in the same place at the same time.

The nucleus of an atom is a fermion or boson:

• whether the sum of the number of protons and neutrons is odd or even
• explains the strange behavior of very cold helium
• a superfluid (no viscosity) because nuclei are bosons and pass through each other.

Fermoins...The Matter Particles:

• Characteristics:
• • subject to Pauli exclusion
  • cannot co-exist in the same location
  • any particle that has odd-half-integer (1/2, 3/2, ...) intrinsic spin
  • measured in quantized units of ; = 1.055 x 10^-34 J s
  • spin is the internal angular momentum of a particle in units of .
    
• Examples of fundamental matter particles:
• • quarks and leptons
  • most composite particles
  • protons and neutrons are fermions.

Bosons...The Fine Particles

• Characteristics:
• • have an integer spin measured in the units of h-bar (spin = 0, 1, 2...)
  • not subject to Pauli exclusion
    
• Examples of fine particle matter:
• • The carrier particles related to all the fundamental interactions
  • Composite particles with even numbers of fermion constituents (such as mesons)