Physics 125: Elementary Particle Physics

Spring 2000

Professor Jeffrey D. Richman

Broida Hall 5131, 893-8408




What is particle physics?

Particle physics addresses the challenging questions: What are the fundamental constituents of matter? How do they interact? The smallest objects observed so far—quarks, leptons, and gauge bosons—behave in a manner that we can now describe in great detail. Yet, in spite of tremendous progress in this field, many fundamental mysteries remain. What is the origin of mass? Why do neutrinos appear to have very tiny masses? Why is there a three-fold replication of a basic set of particles (the generation puzzle)? Are quarks truly elementary particles? Why are some conservation laws violated by a narrow class of processes? Why is there much more matter than antimatter in the universe? Is there, as theorists predict, an undiscovered ``supersymmetric’’ partner for every known type of particle?

To make progress in the study of elementary particles, one needs sophisticated experimental and theoretical tools. We use accelerators of monumental size to produce particle collisions at energies that are equal to those 10-12 s after the big bang. We routinely collide matter with antimatter, destroying the initial particles and creating new ones. The detectors that we use to study these collisions are nearly as impressive. Here at UCSB, the high-energy physics group is very active in constructing such detectors and in analyzing the results of experiments that we perform at various accelerator laboratories.

The theoretical tools required to analyze elementary particle phenomena are also extremely interesting and challenging. Nearly all processes involve phenomena that must be described with relativistic quantum mechanics. Theories must also cope with the fact that, in high-energy collisions, particles are usually created or destroyed. In other words, we don’t simply smash two watches together and observe the little pieces come flying out---entirely new pieces are created! We have come to understand that the "new" particles observed in such experiments are every bit as fundamental and important to piecing together the puzzle of matter as the particles that make up atoms. The theoretical framework for describing these processes is called quantum field theory.

In Physics 125 we will make a start towards understanding the nature of elementary particles and their interactions. We can go quite far without using the full apparatus of

quantum field theory. We will, however, need to use special relativity and quantum mechanics routinely.

Finally, let me repeat a sentiment of a physicist I know. She said that doing particle physics is like climbing a mountain: the journey up can be a struggle, but the view from the top is great!

Some Advice on How to Succeed in this Course

This course will be different from many of your upper division physics courses. You may find it hard to keep track of all the new terminology and ideas. Here is some advice on how to deal with it.

  1. Keep up with the reading and do the homework on time. Take careful notes when you read the textbook and bring lots of questions to class. Come to office hours to get mysterious concepts clarified!
  2. Remember information: constants, particle names and quantum numbers, masses, lifetimes, as much as you can. You may be used to solving idealized problems that are simply meant to give you insight into applying a particular physical law. Here things are different: you need to learn and understand the properties of real physical systems. In order to understand why certain observations are crucial, you must be able to put the information into context. Without the background information in your head, you will have a hard time understanding this context. Creating your own mental database also helps you to develop physical intuition in a subject that is very unfamiliar.
  3. Remember the main results of homework problems. Many of the problems will address important issues; they are not simply cooked-up examples.


Homework, Tests, Grades, and All that Stuff

  1. Homework = 40%
  2. Midterm = 20%
  3. Final = 30%
  4. Paper = 10%

The paper can be on any subject related to particle physics that interests you, subject to my approval. It should be around 10 typewritten pages, although quality is more important than quantity. The paper is due on the last day of class. Each student should meet with me to get approval (and advice!) on a paper topic no later than the week after the midterm. The earlier you get started on this paper the better!


Ph 125: Preliminary Schedule for Spring 2000






Mon, April 3

Energy and length scales of atoms, nuclei, and particles

Intro, Ch 1 (History)


Wed, April 5

Constituents of matter and composite systems

Ch 1 (History), Ch. 2 (Dynamics)


Mon, April 10

Interactions and gauge bosons

Ch. 1, Ch. 2


Wed, April 12

Feynman diagrams: paradigms and examples

Ch. 1, Ch. 2


Mon, April 17

Relativity review

Ch. 3 (Relativistic Kinematics)


Wed, April 19

Relativity in particle physics

Ch. 3


Mon, April 24

Relativity in particle physics

Ch. 3


Wed, April 26

Detection and measurement of particles



Mon, May 1




Wed, May 3

Quantum amplitudes and the nature of scattering and decay processes

Ch. 6; 8.1, 8.2


Mon, May 8

From strangeness to charm and beyond: the discovery of quark and lepton flavors

5.7, handouts


Wed, May 10


Midterm: Lectures 1-10


Mon, May 15

Global symmetries and symmetry breaking: general analysis

Ch. 4


Wed, May 17

Symmetry breaking in the weak interactions: C, P, CP, and T violation

Ch. 4


Mon, May 22

Matter-antimatter oscillations (I)



Wed, May 24

Matter-antimatter oscillations (II)



Mon, May 29




Wed, May 31

Neutrino oscillations



Mon, June 5

The physics of gauge and Higgs bosons

Ch. 10


Wed, June 7

Supersymmetry and beyond