Transcript History of Particle Physics

Introduction to Modern Physics
A (mainly) historical perspective on
- atomic physics
- nuclear physics
- particle physics
Electron discovery 1897 Start of
“Modern
|
Physics”
Atomic Physics
|
Nuclear Physics
|
Particle Physics
A modest
goal !
STANDARD MODEL
|
?? Theory of Everything ??
A lesson from history!!
At the end of the 19th century…
CLASSICAL PHYSICS
Mechanics – Newton 1687
Electromagnetism – Maxwell 1848
Plus…a few loose ends!!
= The End of Physics ??
Then…attempt to predict Blackbody
Radiation
DISASTER !!
Electromagnetic
radiation
Electromagnetic Radiation
Electromagnetic Radiation
c = f
Frequency
Speed of light
3 x 108
meter/second
or
30cm (1 foot)
per nanosecond
Wavelength
(meter)
#vibrations/
second
Theories of
Blackbody
Radiation
Classical
disaster !
Quantum
solution
Planck’s “Quantum Theory”
I(,T) ~ -5 / (ehc/kT - 1)
The “oscillators” in
the walls can only
have certain
energies – NOT
continuous!
About the same time…
the electron was discovered.
So about 100 years ago people believed in
the existence of “atoms”:
- electron is part of an atom?
- atoms emit radiation strangely?
- what else is in an atom?
- atoms emit electromagnetic waves?
Then 1905 !! Einstein’s Miraculous Year
- to be celebrated this year as the “Year
of Physics”
http://www.wyp2005.org/
http://www.einsteinyear.org/
Example…
The Photoelectric Effect
Light = tiny particles!
Wave theory: takes too long to get enough
energy to eject electrons
Particle theory: energy is concentrated in
packets -> efficiently ejects electrons!
An application of the photoelectric effect
So matter contains electrons and light
can be emitted in “chunks”… so what
does this tell us about atoms??
Possible models of the atom
Which one is correct?
The Rutherford Experiment
Electric potential
V(r) ~ 1/r
The “correct” model of the atom
…but beware of simple images!
Probability of
finding electrons
in a hydrogen
atom
Results from
“quantum
theory”
Atomic “signatures”
Rarefied gas
Only discrete lines!
How atomic light emmision “works”
A photon!
But why don’t all our atoms collapse??!!
… if waves can be particles, perhaps
particles can be waves…
 = h/mv
OK !
SELF
DESTRUCTS!
Electrons as waves – an application
A GEM foil
140mm
70mm
1920’s – Full description of atomic
behavior -> Quantum Mechanics
Weird stuff!!
Ghosts!??
…so things get “fuzzy” at the atomic/quantum
level
…in fact we can no longer be certain of
anything!
x ~  (wavelength)
p ~ h/
(x) (p) ~ h
Heisenberg’s
Uncertainty Principle
On to the Nucleus – 1930’s
Existence of protons – Rutherford/neutral atoms
1932 Chadwick discovers the neutron
Note the relative scales!
Nucleus ~ baseball
Atom ~ city
Nucleus
Atomic mass number
A
Z
X
Atomic number
e.g. “Uranium-235”
235
92
U
Nuclide
A=N+Z
…so normally N > Z
“The most important graph in all of science”
Why there are stable
nuclei
Why
the
Sun
shines
Why don’t nuclei fall apart??
Two
Protons
+
No
charge
No charge
No charge
Repel
+
+
No charge
So there MUST be a NEW FORCE
The Strong Nuclear Force
“Pions”
“Gluons”
…more later!
Nuclei can also decay :
Alpha decay e.g.
Alpha particle
Beta decay: n -> p + e + 
Gamma decay e.g.
Applications of Nuclear Physics
Fission:
Fusion:
~limitless
energy ??
Applications of Nuclear Physics
PET
MRI
e+ + e- -> 2
Or:
But still open questions remain…
What’s inside a proton/neutron?
What causes Beta decay?
What other “elementary” particles
exist?
What other forces exist?
Why is the proton mass 1800x the
electron mass?
Where does mass come from?
Introduction
to
High Energy Physics
Research
(or how to chase quarks and
get paid for it)
Structure of Matter
Matter
Molecule
Atom
Nucleus
Baryon
Quark
(Hadron)
u
cm
Mass
proton ~ 1 GeV/c2
10-14m
10-9m
10-10m
Chemistry
Atomic Physics
Nuclear
Physics
10-15m
<10-19m
protons, neutrons, top, bottom,
mesons, etc.
charm, strange,
p,W,L...
up, down
Electron
(Lepton)
<10-18m
High Energy Physics
How do we DO Particle Physics
Use collisions of elementary particles!

Definition: “Study of matter and forces at the
most fundamental level”
Why HEP?: Investment in basic research has
always returned major economic dividends.
?
~ 50% GNP related to “modern physics”
- must keep up flow of new knowledge
or economy/society will stagnate.
History of Particle Physics
Atomic
Nuclear
Physics
Physics
Quantum
Mechanics
Relativity
Ingredients:
-> discovering particles:
e, p, n, m, p, , , , …
-> understanding properties of interactions:
Electromagnetic:  e scattering
Weak nuclear: neutron decay
Strong nuclear: proton-antiproton scattering
(Gravity ??)
-> Finding
patterns
-> Combining forces: e.m. + weak +? strong +??
+ gravity ???
How do we “do” particle physics?
Theory
Phenomenology
Experiment
A constant interplay of
ideas/experiment
Electron discovery 1897 Start of
“Modern
|
Physics”
Atomic Physics
|
Nuclear Physics
|
Particle Physics
A modest
goal !
STANDARD MODEL
|
?? Theory of Everything ??
What do we know now (2004)?
A question of Scales:
Planck scale ~ 10-35
Quarks
 10-19 m
Nucleus
Atom
~10-14 m
~10-10 m
You ~1.5m
Collider detector ~10 m
Accelerator ~104 m
Early Particle timeline
I am born
My career starts!
The recent particle timeline
Revolution!
What next??
Pacific Ocean
I280
“Junipero
Sierra
Freeway”
2-mile
accelerator
Part of Stanford University
The “Mark I”
detector where
the charm quark
was discovered
and a Nobel Prize
was won
Fermilab - Chicago
We have seen that the Standard Model
covers a wide range of phenomena – and
explains them well.
BUT:
- no means of generating mass
- matter asymmetry
- dark matter
- how is electroweak symmetry broken?
- are quarks composite?
Famous scientist as
the Higgs
Supersymmetry
Do all forces become one at
high energy??
UTA and Particle
Physics