Where to learn entry-level particle physics? Like most people, I have been hearing about words like “quarks, hadrons, leptons” since junior high school. However, I have never known the next step for learning more about them. The talk by David Gross during a summer school in Sweden last summer completely aroused interest in this subject.

During the lunar new year season, which was early February this year, I found time to dive into this subject a little. I want to first get an overview of this subject, focusing on building a physical picture and intuitive feelings, avoiding technical details as much as possible. Therefore, I started exploring all kinds of textbooks and videos to searchfor what I want.

*Quarks and Leptons* by Francis Halzen and Alan D. Martin

This book was recommended by my friend, Mark Weitzman, a few years ago. It is certainly not a popular science book for general audience, but a textbook for people who know undergraduate quantum mechanics very well. The first two chapters of this textbook, however, are what I’m looking for. It is a nice overview of several central questions, for example, from what evidence do we start to suspect a particle, like a proton, has inner structure, while some others, like an electron, doesn’t.

Starting from chapter 3, detailed mathematical calculations come up. One of the feature of this textbook is that it only employed one-particle quantum mechanics to describe motions of elementary particles, avoiding a full but much more intricate and complicated field theory treatment. I want to study the details of the book in the future as a preparation for understanding quantum field theory in particle physics context.

## Susskind's Theoretical Minimum: Advanced Quantum Mechanics

Susskind’s Cosmology course has convinced me that whenever I want any intuitive understand of a concept or a subject, I should first check whether he has said something about it. His lectures and Feynman’s lectures share a very similar style. In his supplemental course, I found a series of 3 courses on Particle Physics, and also one course on Advanced Quantum Mechanics. As a warm-up, I first chose to take a look at the Advanced QM class. I found hidden much jewelry.

The first three lectures demonstrate how the rotational symmetry of an atom entails the degenerate structure in hydrogen atom energy spectrum. He then moved on, in the next two lectures, talking about how Pauli discovered the internal spin of electrons by studying this spectrum. There is a very fascinating discussion about the relationship between spin and fermion nature of electrons.

The last 5 lectures focus on developing quantum field theory (QFT) formalism in the non-relativistic case. This exposition is hard to find elsewhere. Most QFT textbook starts by a full relativistic treatment, which makes it very hard to understand its connection with the non-relativistic QM taught in undergraduate time. The last lecture contains many intuitive discussions about the relativistic QFT of electron, Dirac equation, like how to understand the mysterious multi-component form of the electron wave function: where does the spin come and where does the concept of anti-particle comes.

*In Search of the Ultimate Building* Blocks by Gerard 't Hooft

I’m not very satisfied with the first two chapter of Francis Halzen and Alan D. Martin’s textbook, and I want to know more about the story of how people discovered and understand the standard model of particle physics. Again, I remembered the charm of another great physicist, t’ Hooft, during the Sweden summer school, and gladly found that he has written a book about this. It doesn’t feel like a popular science book because sometimes it feels quite detailed and technical. I believe the author has tried his best transitioning mathematical expressions into words. So, it is a very nice and rare book for people like PhD students or physicists who are not familiar with particle physics, since they have enough theoretical background. I feel it prepares me a lot for my future attack on QFT.