## From Anna Phan US/LHC Blog via Quantum Diaries: “What exactly is CP violation?”

*Hey, Anna, nice new picture!!*

“When we look around us, everything is made up of matter – protons, neutrons and electrons. Even looking out into space, all the planets, stars and gas that we can observe is made up of these particles. There is a *cosmological excess* of matter over antimatter which is at odds with the theoretical symmetry between them.

The theoretical symmetry between matter and antimatter is more commonly known to particle physicists as * CP*. If nature treated matter and antimatter alike, then nature would be CP-symmetric. If not, CP is violated.

CP is the combination of two other more fundamental symmetries, **C**harge conjugation and **P**arity. C is the symmetry between positive and negative charge while the P is the symmetry of spatial coordinates.”

*If we take a particle with positive charge, C reverses the charge, meaning the particle will now have negative charge, and vice versa. Note that if we start with a neutral particle, C will have no effect, since it has no charge.*

*P is a little harder to explain, though more intuitive, as we encounter a symmetry of spatial coordinates every time we look into a mirror. I am right handed, but when I look into a mirror, my reflection is left handed. This almost a perfect analogy to the P symmetry in particle physics, which transforms left handed particles to right handed ones. *

*So the combination of CP on a left handed, negatively charged particle would transform it into a right handed, positively charged particle.*

For the full story, see Anna’s post here.

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