"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


interacting via forces mediated by vector bosons
W+, W-, Z0
as a consequence of gauge symmetries

SU(3)Colour(strong) ¥ SU(2)weak ¥ U(1)em

Unresolved questions:

Nuclear physics

Experimental Subatomic Physics

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
  teamGeiger(RA), cast of thousands
  beama particles
  (Rd, ~5 MeV)   (Tevatron, 900 GeV)
  target foil (Au,Ag) beam
  detector ZnS screen 10000 ton hermetic
  + eyeball   detector
  DAQpencil networks, workstations,
   (data acquisition)   + disks, tapes, ....
  analysis student+pencil~102 students + computers