|MadSci Network: Physics|
Hi Jagmeet, That's right! I would point out that when you say "opposite parity", you have to think about both the particle's direction-of-travel, and also its spin direction. In a parity transformation, you have to reverse the direction but NOT the spin. OK, so let us start with an electron traveling north-west, with its angular momentum vector pointing up. When you flip the parity, you'll get an electron traveling south-east, with its spin still pointing up. If you now reverse the sense of time, the particle will be going north-west again, and now its spin will be pointing down. A charge-congugation turns the - charge into a + charge, and now you've got a spin-down positron traveling northwest; exactly the CPT "mirror" of the original situation. (Due to the properties of the weak interaction, we expect electrons and positrons to have opposite spins, or more correctly opposite "handedness", in many situations. Indeed the CPT reversal generates electrons and positrons with the correct handedness.) So you're right, we can't tell the difference between a CPT-reversed electron, and an "ordinary" positron. -Ben
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