Over the last couple weeks I’ve been reading several popular or semi-popular books about particle physics. I thought I’d make a few comments about them here.
The first one is called The Quantum Quark by Andrew Watson. It covers the Standard Model and its history, concentrating on quantum chromodynamics, the theory of the strong interaction. By limiting itself in this way, it is able to go into a much deeper, more detailed study of the theory than would otherwise be possible in a popular book. While avoiding the use of equations and trying to stick to as accessible a level as possible, the author manages to discuss a wide range of aspects of QCD not treated in any other book of this kind. These topics include a detailed description of jet phenomena in perturbative QCD, the behavior of quark structure functions (including their still mysterious spin dependence), the delta I=1/2 rule for non-leptonic weak decays, and many others.
The book contains several amusing stories I hadn’t heard before, including the origin of the term “penguin diagram” to refer to a certain class of Feynman diagrams. Supposedly John Ellis and Melissa Franklin were playing darts one evening at CERN in 1977, and a bet was made that would require Ellis to somehow insert the word “penguin” in his next research paper if he lost. He did lose, but was having a lot of trouble figuring out how he would do this. Finally, “the answer came to him when one evening, leaving CERN, he dropped by to visit some friends where he smoked an illegal substance” (the only time he ever did that, I’m sure..). While working on his paper later that night “in a moment of revelation he saw that the diagrams looked like penguins”. I’d always wondered why these diagrams had been given that name, they never looked very much like penguins to me. But then again I never tried looking at them under the same conditions as Ellis.
Witten makes an unusual appearance here, as Watson discusses Witten’s Ph.D. thesis, the topic of which was the use of asymptotic freedom to study the photon structure function using deep-inelastic photon-photon scattering.