You discovered CP violation!

The Mystery of CP Violation

The study of CP violation is concerned with some very fundamental questions:

What is CP?

CP is a possible symmetry of nature. If the laws of nature were symmetric under CP, then matter and antimatter would be governed by the same rules. This means that if we communicated with aliens from a distant galaxy, there would be no way to find out if they are made from matter or antimatter: No experiment they could perform would allow us to deduce if they lived in a matter or antimatter world. On the other hand, if there was a fundamental difference between matter and antimatter, such an experiment would be possible. It turns out that this is the case in our universe!

How was CP violation discovered?

In 1964, a team lead by Val Fitch and Jim Cronin performed experiments with neutral Kaons, particles formed by a strange and an anti-down quark. These neutral Kaons have the amazing property that they can spontaneously transform into their own antiparticle. Fitch and Cronin discovered that the rate at which these Kaons changed from matter to antimatter and vice versa was different, clear evidence for CP violation! This discovery came as a total surprise to physicists (it was assumed that nature was symmetric under CP) and earned Cronin and Fitch the Nobel Prize in 1980.

How is CP violation currently understood?

In 1973, two Japanese physicists, Makoto Kobayashi and Toshihide Maskawa, found a very simple and elegant way to explain the occurrence of CP violation in our universe. The only problem: The explanation required a third generation of quarks (the top and bottom quarks) for which there was zero evidence at the time.

This turned out to be an incredible prediction, when both of these quarks were discovered decades later. So far, the idea of Kobayashi and Maskawa, called the CKM mechanism, has been able to explain every single occurrence of CP violation that physicists managed to detect in the lab. They were awarded the Nobel Prize in 2008.

What's next for CP violation?

CP violation is one of the necessary ingredients for explaining the abundance of matter over antimatter in our universe. But there is one problem: The CKM mechanism predicts too little of it. The amount of matter in our universe suggests that a correction or even a complete revolution in our understanding of CP violation is necessary.

CP violation remains a hot topic in Physics research. Specialized experiments like the LHCb detector at CERN in Switzerland are currently searching for hints of New Physics that could explain how our universe came to be the way it is.

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