Conservation of Total Spin in the Stern Gerlach Experiment

[CassiopeiaA]

I just started reading Stern Gerlach Experiment and this thought crossed my mind. Totally a hypothetical question. If I pass an electron and positron through separate SG apparatuses, I will know in which spin state each particle has collapsed. But afterwords I let electron-positron pair annihilate to produce 2 photons. I let these photon Interact with each other and again produce an electron-positron pair. So, if I again check the spin state of these particles separately, in the same direction as before, will I get the same result or is it again completely random?

P.S. I am just a school student trying to learn something difficult for me to understand. So please spare my ignorance.

 

[PeterDonis]

if I again check the spin state of these particles separately, in the same direction as before, will I get the same result

No. The sequence of operations you describe will conserve the total spin, but it will not conserve the individual spins of the particles.

 

[CassiopeiaA]

No. The sequence of operations you describe will conserve the total spin, but it will not conserve the individual spins of the particles.

Oh Okay. So there is no known correlation between photon polarization and spin of electron-positron pair in case of pair production?

 

[PeterDonis]

So there is no known correlation between photon polarization and spin of electron-positron pair in case of pair production?

Not for the individual particles. As I said, only the total spin is conserved.

 

[CassiopeiaA]

Not for the individual particles. As I said, only the total spin is conserved.

Okay thanks.