"All these things being considered, it seems probable to me that God in the beginning formed matter in solid, massy, hard, impenetrable, moveable particles of such sizes and figures, and with such other properties, and in such proportion to space, as most conduced to the end for which he formed them; and that these primitive particles being solids, are incomparably harder than any porous bodies compounded of them; even so very hard, as never to wear or break in pieces; no ordinary power being able to divide what God himself made in the first creation. While the particles continue entire, they may compose bodies of one and the same nature and texture in all ages: but should they wear away, or break in pieces, the nature of things depending on them would be changed. Water and earth, composed of old worn particles and fragments of particles, would not be of the same nature and texture now, with water and earth composed of entire particles in the beginning. And there, that nature may be lasting, the changes of corporal things are placed only in the various separations and new associations and motions of these permanent particles."

                      Isaac Newton - Optics

Nuclear and Particle Physics

Particle Physics is the discovery and measurement of the fundamental constituents and their basic interactions.

Particle Physics is not all of physics.

   Æ Complex systems require new concepts,

e.g. Superconductivity

Particle Physicists try to ignore multibody systems.

Nuclear Physics is the study of the simplest complex systems constructed from the fundamental constituents.

Together, nuclear and particle physics are sometimes called Subatomic Physics.

The Particle Physics Universe

Constituent point fermions

   Quarks:

   Leptons:

interacting via forces mediated by vector bosons

photons

gluons

W⁺, W^-, Z⁰

as a consequence of gauge symmetries

Unresolved questions:

• This model will breaks at energies above about 1 TeV.
• Why do particles have mass?
• Why is there more matter than antimatter in the universe?
• What is most of the universe made of?
  

Nuclear physics

• What can you make from quarks and leptons?
  • protons & neutrons
  • nuclei
    • How many elements?
  • reactors
  • stars
    • How do they shine?
      • solar neutrino problem!?
  • quark-gluon plasma?
    

• What happens when the things you make fall apart?
  • alpha, beta, gamma radioactivity
  • nuclear fission
  • supernovae
    • neutron stars and black holes
      • nuclear equation of state?
        
        

Experimental Subatomic Physics

• Some subatomic physics experiments look in nature:
  • to study naturally occurring subatomic processes
  • to look for new particles or processes
• but most experiments usually bang things together to see:
  • how big they are,
  • what they are made of,
  • how they interact,
  • how they can be excited, and
  • what new particles are produced.
• In order to extract this information from experiments,
  • We need to know:
    • what we are banging together,
    • their energy, and
    • their luminosity.
  • We need to measure (as best we can)
    • the types of particles produced in the collision,
    • their energies, and
    • their angles.

After analysis, the information from the experiments is usually expressed in terms of production cross sections and particle masses, excitation energies, lifetimes, etc.

Theoretical ideas are tested by comparing predictions and observations.

The first two subatomic particles to be discovered were the electron and the nucleus. The concepts used in their discoveries are still used today - just vastly scaled up in energy, size, money, and people.

Thompson's discovery of the electron was the first example of a non-accelerator particle search experiment. Thompson showed that cathode rays were electrically charged particles with a fixed value of e /m. Since e was roughly known, he showed that the cathode particles were ~2000 times lighter than a hydrogen atom. Atoms were considered to be the indivisible fundamental constituents of matter, so nothing lighter was expected to exist.

	Rutherford	CDF
team	Geiger(RA),	cast of thousands
	Marsden(UG)
beam	a particles
	(Rd, ~5 MeV)	(Tevatron, 900 GeV)
target	foil (Au,Ag)	beam
detector	ZnS screen	10000 ton hermetic
	+ eyeball	detector
DAQ	pencil	networks, workstations,
(data acquisition)		+ disks, tapes, ....
analysis	student+pencil	~102 students + computers