Fundamental Particles
(The Standard Model)
Nathan Brown
June 2007
Part I
Fundamental Particle – The Meaning
It is understood that the universe is
composed of particles.
Democritus (born 450 BC, Greece) first
introduced the particle nature of
creation.
The term he used to describe the
particle translates in English as “atom.”
Since Democritus, much work was done that
led to the understanding that the “atom”
was actually composed of three smaller
particles (electrons, protons, and neutrons).
As late as the 1930s these subatomic
particles were thought to be indivisible,
elementary (“having no smaller constituent
parts”) or structureless.
Since the 1930s, it was determined that the
proton and neutron, along with 100+ other
particles, are composed of yet smaller
particles known as quarks/antiquarks. These
particles composed of the new
quarks/antiquarks are collectively called
hadrons.
Electrons, part of a larger group collectively
known as leptons, continue to appear
structureless/fundamental or elementary in
nature.
Currently, the leptons and quarks
appear to qualify as the true
fundamental/elementary particles;
meaning without structure.
Part II
The organization of known fundamental
particles – The Standard Model
“The standard model of particle
physics is a theory which [currently]
describes three of four known
fundamental interactions between the
elementary particles that make up all
matter…
It is a quantum field theory developed
between 1970 and 1973 which is
consistent with both quantum
mechanics and special relativity.”
“…the standard model falls short of
being a complete theory of fundamental
interaction, primarily because of it’s
lack of inclusion of gravity, the fourth
known fundamental interaction.”
The particle nature of the standard
model consists of two groups:
- Matter Particles
- Force-Mediating Particles
Matter Particles
The matter component of the Standard
Model is comprised of twelve particles.
These particles all have an intrinsic
spin value of ½, making them conform
to the Pauli Exclusion Principle.
All matter particles of the Standard Model
also have corresponding antimatter particles.
These particles breakdown into groups of
quarks (up, down, strange, charm, top, and
bottom) and leptons (electron, muon, tau,
and corresponding neutrinos).
Quarks and leptons are further grouped into
sets known as generations.
Quarks carry color charges (red, blue,
or green) so they participate in strong
interactions.
The up, charm, and top quarks carry
the electric charge (+2/3).
The down, strange, and bottom quarks
carry the electric charge (-1/3).
This allows the quarks to participate in
electromagnetic interaction.
Leptons are color neutral and do not
participate in strong interaction.
The electron, muon, and tau particles
carry the electric charge (-1) and
participate electromagnetic interaction.
Neutrinos have no electric charge and
do not participate in electromagnetic
interactions.
Quarks and leptons carry flavor
charges and participate in weak nuclear
interactions.
Force-Mediating Particles
Force-mediating particles of the
Standard Model group into three
categories that correspond with three
of the four fundamental interactions.
All three mediating particles are bosons
and have intrinsic spins of (1).
This allows these particles to not
conform to the Pauli Exclusion
Principle.
Photons are electromagnetic force
mediators involving charge particles.
Photons are considered massless
particles.
W+, W-, and Zo gauge bosons are weak
nuclear mediators involving particles of
different flavors (quarks and leptons).
W+, W-, and Z0 bosons are massive
particles.
Gluons are strong nuclear forcemediators involving color charged
particles (quarks).
Gluons are considered massless
particles.
Part III
The Higgs particle – The Challenge
The Standard Model predicts the
existence of one more particle known
as the “Higgs boson.”
The Large Hadron Collider (LHC) at
CERN is hoped to confirm the
existence of the Higgs boson in the
near future.
References
• http://en.wikipedia.org/wiki/Standard_Model
• http://www2.slac.stanford.edu/vvc/theory/fundamental.html
• Google images