Lecture 1: Atoms to Quarks: Macroperiodicity Reflects Microstructure

Musical/Philosophical Prelude:  Die Dreigroschenoper ("The Threepenny") Opera by Kurt Weill.

Age of Light, Electricity and Magnetism
each hot element produces its mysterious, characteristic, sharp
series of line spectra of light...like chords of music
H, He gas discharge
NaCl in flame
see spectra charts
cold gases absorb the same lines
...helium discovered in the atmosphere of the sun before on earth
Fraunhofer lines in sun's atmosphere lines doppler shifted if source moves
electricity comes in 2 "charges"...can separate mechanically

1. Before class EXPERIMENT: Spectral Lines
Get your diffraction grating, a series of minature prisms that acts as one big prism.  Look at a bright light bulb to find the rainbow off to the side.  Look at Hydrogen & Helium gas discharge tubes to see their characteristic spectral emission lines.

2. Introduction:
Atoms, Nuclei, Quarks, Gluons... and Weak, Electromagnetic, and Strong Forces
People have long asked, "Of what is the world made?" and "What holds it together?"

3.  Elementary Particle History:
1897 Thompson "sees" the electron centennial anniversary of elementary particles
DEMO: one volt characteristic of chemical energy = 1 lemon
DEMO: electric charges come in + (glass) and - (fur); high energy UV photons of light knock out electrons; but IR light does not

4. Electron Diffraction
DEMO: electron beam

5.  Distorted Atomic Model
Particles "randomly" found within theirregions:        electrons within atom,  protons and neutrons within nucleus,  quarks within nucleons but probability of finding them,  at any place, with any momentum, at any time represented by the green or brown density

6. The Four Elements:
Greek: philosopher Empedocles in the 5th century BC classified the fundamental elements: earth, air, fire, and water
Chinese: Pinyin WU XING proclaimed the five basic components: earth, wood, metal, fire, and water
Indian: Ishvarakrsna (c. 3rd century AD), five gross elements: space, air, fire, water, and earth
...what are the most fundamental (smallest) entities that cannot be further subdivided?

7. Prescience of the Greeks: Atoms (Introduction to Atoms)
Is something more fundamental than earth, water, air, and fire?
By convention there is color, by convention sweetness, by convention bitterness, but in reality there are atoms and space. Democritus (400 BC)
....but is the atom fundamental?

8. Are Molecules Fundamental?
chemists of 1800's found that all compounds come in fixed ratios: e.g. H₂O, CO₂
DEMO: crystals and their models (e.g. NaCl),
spectral line fingerprints from base "elements" emitted if hot, in a spark, or in a gaseous discharge
in class experiment on H, He lines + spectral charts. Applications: diagnostics, forensics, medicine
absorption lines if a cool cloud between source and observer (e.g. sun's, earth's atmosphere)
DEMO: spectral chart a) emission b) absorption - Frauenhafer lines from sun's atmosphere
sodium D lines from torch and salt

All complex molecules made up of atoms of basic "elements"-
      held together by (residual) electric force
      atoms the smallest piece with same characteristics

9. Periodic Chart of the Elements
Similar chemical and physical characteristics are grouped vertically, getting heavier as one goes down the chart. Number of electrons in each shell (row) increase going right.
DEMO: different types - crystallography, chemical properties

10. Filled Atomic Levels
..atomic levels fill up as electrons added
electrons have spin, up and down
only one electron per allowed state
filled shell = nobel element
1 excess = donor
1 too few in a shell = electron sucker

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

Fermions...The Matter Particles
       electrons, nucleons...leptons and quarks
       particles with internal angular momentum,
             intrinsic spin = 1/2 integer
subject to Pauli exclusion...only 1 in each state

Bosons...The Force Particles
       photons, gluons...
              integer intrinsic spin = 0, 1
not subject to Pauli exclusion...all can occupy

12. Electron Orbitals
..probability distributions of electrons and "standing waves" in atoms

13. Is the Atom Fundamental?
Around 1900, people thought of atoms as tinyballs.  But periodicity in chemistry, in light emission, in the form of crystals
....the macroscopic reveals microscopic structure
...but Rutherford probes into atom... energetic particles reveal structure:
a positive, dense nucleus and a cloud of electrons (e) held together by electric force, carried by photon

14. Period Chart of the Nuclei
Number of protons and neutrons in nuclei
green square = stable nucleus
yellow square = radioactive nucleus
no square = no known nucleus
...easier to put neutrons (0 charge) together
than protons (+ charge repel)
...the bigger the nucleus, the more neutrons
you can stuff in between protons

...put in too few or too many - nucleus falls apart

15. Is the Nucleus Fundamental?
Again, periodicity of nuclear properties... mass, decay cascades, etc. suggest that nucleons fill quantum shells, just like electrons in the outer regions of atom
DEMO: Periodice chart of nuclei
Scientists found the nucleus composed of nucleons:
      neutrons (n) discovered by Chadwick (1932) and protons (p)
only differ in electric charge, mass (m_n>m_p)
held together by (residual) strong force, broken apart by the weak force

16. Are Protons and Neutrons Fundamental?
But up and down quarks are points, confined roughly to the volume of the nucleon
Even protons and neutrons aren't fundamental, comprised of more fundamental particles ... quarks
No evidence that quarks and electrons are not fundamental ...an experimental question ...pointlike to the resolution of the best microscopes

17. Periodic Table of Mesons and Baryons - circa 1964
pion family - mesons (medium weight) hadrons = strongly interacting particles

nucleon family -  baryons = heavy hadrons

excited nucleon family - hyperons
 the "missing" omega minus ...discovery of the ??? clinched the 2D periodicity of elementary particles

18. Charm Discovery - totally unexpected (1974)
all the 2D charts...became 3 dimensional periodic tables of mesons and baryons ...verifying the quark model

19. The Standard Model
describes all experiments on matter and forces in the universe (except for gravity), explains hundreds of particles
complex interactions understood in terms of fundamental particles and interactions
The fundamental entities are:
  Matter Particles: composites of more fundamental particles, leptons (electrons etc.) and quarks ... the fermions
  Force Carrier Particles: each fundamental interaction "carried" by a force-carrier particle: photons,   gluons, w bosons.

20. Periodic Chart of Fundamental Particles (Version I)
Similar properties occur in columns; change decreases going down; quarks and leptons have identical structure - both are matter particles borons (force carrying particle) behave

21. Periodic Chart of Bosons and Fermions (Version II)
Matter particles (fermions) get heavier going down the columns, bigger change moving to the right

22. Periodic Chart of Elementary Particles (Version III)
one 4x4 matrix

23. The Scale of Things
atom made of nucleus and electrons held together by electromagnetism
nucleus made of protons and neutrons held together by strong force (and sometimes, broken
apart by the weak force)
protons and neutrons made of quarks held together by gluons
quarks made of ??? held together by ???
possible that they have no size at all possible that they are not fundamental composites of more
fundamental particles