# Introduction to Particle Physics

“It doesn't matter how beautiful your theory is, it doesn't matter how smart you are. If it doesn't agree with experiment, it's wrong.”
— Richard Feynman

“A theorist today is hardly considered respectable if he or she has not introduced at least one new particle for which there is no experimental evidence.”
— Steven Weinberg

“In the history of physics, every time we've looked beyond the scales and energies we were familiar with, we've found things that we wouldn't have thought were there.”
— Lisa Randall

Welcome to Physics 380! In this class we will study the standard model of particle physics. The topics to be covered include symmetries, conservation laws, scattering, accelerator physics, and the theories that describe the electromagnetic, weak, and strong interactions.

## Assignments

Homework will be assigned on a regular basis. There will be five assignments, and they will all be collected and graded. Current and past assignments will be listed below. Solutions are available, but I am no longer making them downloadable — please stop by my office if you'd like to see the solutions for a particular assignment.

Working with your classmates on these assignments is strongly encouraged. But you should only hand in work that you've completed on your own. If your solution looks just like someone else's work then you need to go back and redo it. If you can't explain each step of your solution then you haven't completed the problem on your own. Remember: the only way to be ready for the exams is to do the homework yourself.

A Warning

Never, ever hand in an assignment that has been copied from a solutions manual or online source. You won't learn anything that way, and it will earn you a grade of zero for that assignment. If it happens more than once it will be reported to the Department Chair and the Dean. Consider yourself warned. Click here to see the College of Arts and Sciences Statement on Academic Integrity.

Grades in the course are determined by homework assignments and exams. The homework assignments constitute 50% of your final grade in the class, one midterm exam (date TBA) counts for 20%, and a final exam due at 9:00 AM on December 8 is worth 25%. The remaining 5% depends on attendance and participation. Asking questions, taking advantage of office hours, and attending all the lectures will earn you the full 5% — see the pdf syllabus for more details.

## Textbooks and References

The main text for the class is Introduction to Elementary Particles by David Griffiths. The tone of the book is just as casual and accessible as his E&M book. There are lots of other books on the subject that you might want to look at as secondary references. Two that I can recommend are An Introduction to Particle Physics and the Standard Model by Robert Mann, and Introduction to High Energy Physics by Donald Perkins. Those texts might be useful if something in Griffiths isn't clear.

1. Introduction to Elementary Particles
David Griffiths
2. An Introduction to Particle Physics and the Standard Model
Robert Mann
3. Introduction to High Energy Physics
Donald Perkins

None of these books are especially recent. (Griffiths is from 2008, Mann was 2009, and Perkins has a positively ancient publication date of 2000.) In fact, they were all written before the confirmation of the Higgs boson! Nevertheless, they are all give good treatments of the material we're going to cover.

One way to get a more recent take on course material is to explore the wealth of notes and papers made available online by researchers. Feel free to sort through what's out there, and let me know if you have questions about a particular resource. But be warned: not all references are created equal! Some people are extremely careful and you can trust whatever they commit to paper. Others have a more relaxed attitude towards consistency and reliability. And everyone does things a little differently, so it's easy to mix up conventions between references. If you aren't careful, things can get messy as you try to translate factors of i and minus signs between sources!

From time to time I will post notes and lectures that supplement the material from the book. These will be posted in the next section.

Finally, one of the most valuable references as you learn about particle physics is the Review of Particle Physics maintained by the Particle Data Group at Lawrence Berkeley National Laboratory. This is an up-to-date catalog of essentially everything we know about the sub-atomic world, and how we know it. Need to know the mass of an exotic meson? Check the PDG. Curious about the different decay modes of some heavy baryon? Head over to the PDG. If they don't have it, we don't know it. You can find a link in the next section.

## Notes, Tables, and Figures

Links to material in peer-reviewed journals appear in red.

2014 Review of Particle Physics
Author: Particle Data Group (Lawrence Berkeley National Laboratory)
Source: K.A. Olive et al. (Particle Data Group), Chin. Phys. C38, 090001 (2014)
This is a link to pdgLive, the interactive version of the 2014 Review of Particle Physics. Print and pdf versions of the review are available at the PDG website.

Clebsch-Gordon Coefficients
Author: Particle Data Group (Lawrence Berkeley National Laboratory)
Source: J. Beringer et al. (Particle Data Group), Phys. Rev. D86, 010001 (2012)
Adding two angular momentum eigenstates together? This table of Clebsch-Gordon coefficients, courtesy of the PDG, will help. Their street address is “1 Cyclotron Road” so they probably know what they're talking about.

Lectures on the Symmetries and Interactions of Particle Physics
Author: James Wells (University of Michigan)
Source: http://scholardox.com
These lecture notes by University of Michigan particle physicist James Wells give a beautiful review of the symmetries (spacetime and internal) of the standard model.

This short Mathematica notebook builds up the “spinor” representation of SO(3), with $$2\times2$$ matrices as the generators. It shows that the generators $$S^{a} = \frac{1}{2}\sigma^{a}$$ have the correct properties, builds up the full transformation matrices using Mathematica's built-in matrix exponentiation, and relates the two-component spinors to the familiar spin-$$\frac{1}{2}$$ states you learned about in Quantum Mechanics.

Renormalization of a Model Field Theory
Author: David Griffiths and Per Kraus (Reed College)
Source: American Journal of Physics, 60, 1013 (1992)
In class we'll use a "toy field theory" to help us understand how to calculate scattering and decay amplitudes with Feynman diagrams. But we will only perform tree level calculations. That is, we won't consider quantum mechanical corrections to the quantities we calculate. Sorting out the quantum part of quantum field theory introduces several new complications that are discussed in detail in this paper. (By the way, Griffiths' co-author was a Reed College undergrad who is now a professor at UCLA.)

## Motivation

Anything worth learning can be put on a cupcake.