What is CP Violation? Simplified Explanation

[Kvm90]

Can anyone explain CP violation in as simplistic a fashion as possible? I just can't understand really in depth versions I am finding online.

 

[The_Duck]

Since antimatter particles seem to be exactly the same as matter particles except that their charges are flipped, you might expect that if all particles were secretly replaced with their antiparticles the universe would continue on as before with no observable differences. This replacement operation is called C, short for "charge conjugation." The expectation that the universe would be unaffected by the C operation is in fact incorrect: we say that "C symmetry is violated." For instance, all neutrinos are "left-handed" (which means their spin axis is oriented in a certain way with respect to their direction of motion), but all antineutrinos are right-handed. C turns a left-handed neutrino into a left-handed antineutrino; i.e. it turns a physical particle into one that doesn't normally exist, so the universe after C would be very different from the universe before C.

P, or "parity" is a different operation in which you basically reflect the universe through a mirror. You might expect that if you reflected the universe through a mirror no one would notice a difference--for instance, our hearts would now be on the right side of our chests but our brains and everything else would get flipped too, so we would call that side the left side. One effect of P is that it flips the handedness of particles. So P symmetry is also violated by neutrinos: applying P to a left-handed neutrino gives a right-handed neutrino, which doesn't exist in the normal universe.

Now, you might ask about CP, the operation you get by compounding C and P, which turns all particles into antiparticles and then reflects the universe through a mirror. CP turns a left-handed neutrino into a right-handed antineutrino, which actually exists! So maybe we would not notice a difference if someone secretly applied the CP operation to the universe. Alas, even this is not true: CP symmetry is violated. The violation is not as dramatic as with neutrinos but there are some processes that would occur slightly differently in the charge-conjugated, mirror-flipped universe.