image of space

The revolution

The discovery of the J/ψ caused such a shift in thinking that the period is called the November Revolution. Here’s how we built up to that moment.

The background

Accelerator physics. Einstein predicted that mass and energy are actually interchangeable, but it takes a lot of energy to produce a little bit of mass. So physicists started smashing particles into other particles, concentrating the energy to make new particles. These particles are not normally seen because they give up their mass in the form of energy, downsizing into ordinary particles – such as protons, neutrons and electrons. They typically do so very quickly, in just a nanosecond or less.

The breakthroughs

1947

The “pi meson” is discovered, kicking off the accumulation of a “particle zoo.” These particles, discovered with accelerators, were thought at first to be elementary particles – the smallest particles, from which everything else is made. But as the community closed in on a hundred of them, researchers doubted that they were truly elementary.

 

1964

Physicists first propose the “quark” model of matter: the particles in the zoo are actually combinations of quarks. The three quarks, as well as their antiquarks (which are like the negatives of the quarks – opposite in electrical charge and other characteristics), could explain the known particles: they were called “up,” “down” and “strange.”

 

1970

The existence of a fourth quark, the charm quark, is predicted.

 

Monday, November 11, 1974

Sam Ting, a physics professor at MIT, and Burton Richter, a physicist at the Stanford Linear Accelerator Center, make a joint announcement. In two different experiments, they had discovered the same particle. Ting’s group called it the J particle. Richter’s named it ψ (psi).

the new model

The weird thing about the J/psi is its very long lifetime combined with a high mass. It didn’t fit any predictions. Eventually, the community realized that the J/psi was made up of a fourth quark, dubbed the charm quark, and its antiparticle. The quark model officially took over. Ting and Richter were awarded the Nobel Prize in physics in 1976.