Introduction to Modern Physics A (mainly) historical perspective on - atomic physics - nuclear physics - particle physics

Electron discovery 1897 | Atomic Physics | Nuclear Physics | Particle Physics STANDARD MODEL | ?? Theory of Everything ?? Start of “Modern Physics” A modest goal !

A lesson from history!! At the end of the 19 th 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

c = f Speed of light 3 x 10 8 meter/second or 30cm (1 foot) per nanosecond Wavelength (meter) Frequency #vibrations/ second

Theories of Blackbody Radiation Classical disaster ! Quantum solution

Planck’s “Quantum Theory” I(,T) ~ -5 / (e hc/ 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”

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?

Electric potential V(r) ~ 1/r The Rutherford Experiment

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… OK ! SELF DESTRUCTS! = h/mv

Electrons as waves – an application 70  m 140  m A GEM foil

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! Atom ~ city Nucleus ~ baseball

Nucleus X A Z Atomic mass number Atomic number Nuclide e.g. “Uranium-235” U

A = N + Z …so normally N > Z

“The most important graph in all of science” Why the Sun shines Why there are stable nuclei

Why don’t nuclei fall apart?? ++ Repel Two Protons 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 MRI PET 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 cm m m m u < m m MatterMoleculeAtomNucleusQuarkBaryon Electron < m protons, neutrons, mesons, etc.  top, bottom, charm, strange, up, down Chemistry Atomic Physics Nuclear Physics High Energy Physics Mass proton ~ 1 GeV/c 2 (Hadron) (Lepton)

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 Physics Nuclear Physics Quantum Mechanics Relativity

Ingredients: -> discovering particles: e, p, n,      … -> understanding properties of interactions: Electromagnetic:  e scattering Weak nuclear: neutron decay Strong nuclear: proton-antiproton scattering (Gravity ??) -> Finding -> Combining forces: e.m. + weak +? strong +?? + gravity ??? patterns

How do we “do” particle physics? A constant interplay of ideas/experiment Theory Phenomenology Experiment

Electron discovery 1897 | Atomic Physics | Nuclear Physics | Particle Physics STANDARD MODEL | ?? Theory of Everything ?? Start of “Modern Physics” A modest goal !

What do we know now (2004)?

A question of Scales: Planck scale ~ Quarks  m Nucleus ~ m Atom ~ m You ~1.5m Collider detector ~10 m Accelerator ~10 4 m

Early Particle timeline My career starts! I am born

The recent particle timeline Revolution! What next??

Part of Stanford University Pacific Ocean 2-mile accelerator I280 “Junipero Sierra Freeway”

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