Elementary Particles

Elementary
Particles
--------------------------

Joseph F. Alward, PhD
Department of Physics
University of the Pacific

Until 1932, the "elementary" particles were the electron,
proton, and neutron. We now know of hundreds of other
elementary particles.

Pion Production

Hidekei Yukawa (1907-1981)

In 1935 Yukawa predicted
existence of pions, which
were finally discovered in
1947.
Pion decays into two gamma photons in
0.8 x 10^-16 s.

Matter from Energy

Other elementary particles can be created out of thin air
from pure energy; the positron, for example.

Antiparticles

Paul Dirac (1902-1984)
1933 Nobel Prize
In 1928 Dirac redicted the
existence of the positron

The positron was discovered in 1932 by C.D.
Anderson.
In this false-color cloud chamber photograph a
gamma-ray photon disappears and in its place
appear an electron and its antiparticle, the positron,
a particle of equal mass but opposite charge.

Missing Energy in Beta Emission
(Leads to discovery of another elementary particle)

Electron (beta particle) doesn't have the same
kinetic energy each time. Why?

The Neutrino

Wolfgang Pauli, Austrian
physicist (1900-1958)

In 1931 predicted existence
of a particle which Enrico
Fermi called "neutrino".
1945 Nobel Prize

The neutrino was found in 1956. It is believed to have
zero charge, and practically zero mass.

The Anti-Neutrino

The antineutrino carries away the "missing" energy.

Neutrinos from Supernova

Supernova 1987A
170,000 light years
away emitted a blast
of neutrinos traveling
near the speed of light.
Two hours later the
supernova began
emitting a blaze of
light a million times
brighter than the Sun. Today, every square
centimeter on Earth is
struck by a neutrino
each second.

Positron-Electron Annihilation

The positron is the anti-particle to the electron, and vice-versa.
When they come together, they annihilate one another; pure
energy appears in their place in the form of gamma photons
moving in opposite directions.

Positron Emission Tomography

"tomos": slice
₈O¹⁵ -------> ₇N¹⁵ + ₁e⁰ then ₁e⁰ + _-1e⁰ -------> g + g

PET Scan Image of Brain

Healthy brain Brain with Alzheimer's
disease

Material Particles

Leptons

Examples:

muon (-)
electron
neutrino
-----------------
No internal
structure Hadrons

Examples:

neutron
proton
pion (+)
----------------
Believed to
contain
quarks.

(The pion is also called a pi-meson.)

Quarks

Hadrons

Examples:

neutron
proton
pion (+)
----------------
Believed to
contain
quarks.
Murray Gell-Mann took
the name quark from
"Three quarks for muster
Mark", in James Joyce's
book Finnegan's Wake.
(1963)
Whimsical names--
called "flavors"--for
the quarks.

Molecules, Atoms, and Nuclei

Nuclei, Nucleon, and Quarks

Quark Charge

The neutron
contains three quarks. Which three quarks
could be used to make a neutron?

The proton
contains three quarks. Which three quarks
could be used to make a proton?

The pion
has a charge of +1 and contains two quarks.
Which two quarks--if any--could be used to
make a pion?

Quarks and Anti-Quarks

The Pion
(Two quarks; charge: + 1)

Which two quarks could
be used to make a pion?
The Neutron
(Three quarks; charge: 0)

Could a neutron have
one or more antiquarks?

Quark Structure of the Pion, Proton, and Neutron

Quark Color Causes Strong Force (Nuclear Force)

Moo-Young Han, Duke Univ In 1965 Moo-Young Han and Yoichiro
Nambu suggested quarks possess color.

The "color" attribute is not traditional color;
the name is somewhat arbitrary, and almost
as whimsical as the names of the quarks.
Color is also called
color charge.

Like colors repel.
Unlike attract.

Color-AntiColor
attraction is
stronger.

Blue-AntiBlue
stronger than
Blue-Red, for
example

Quark-Containing Particles are White

Protons and neutrons contain
three quarks:

Protons and neutrons each
contain a red, blue, and
green quark.
Pi-mesons contain only two quarks.
For example:

Anti-red is white light minus red,
or, blue-green.

Quarks Exert Force by Exchanging Color

      Material particles:

Leptons
Examples:

muon (+)
electron
neutrino
-------------
Leptons
contain
no quarks Hadrons
Examples:

neutron
proton
pion (+)
-----------
Hadrons
contain
quarks

    Color charge is the cause of the color force, also known as the
    strong force.

Quarks and Gluons

The strong force is caused
by the emission and
absorption of gluons.

Rule: Sum of colors conserved

Red-antigreen gluon is
emitted by a red quark,
which is transformed to
a green quark.

A green quark, not shown,
absorbs the red-antigreen
gluon and becomes a
red quark.

Source of this page: http://sol.sci.uop.edu/~jfalward/elementaryparticles/elementaryparticles.html

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