Can a Positron be Turned into an Electron?

[Alex K]

The truth is it depends. In the Standard Model without neutrino masses it seems impossible because of a thing called lepton number conservation, but if neutrinos are their own antiparticles, it is possible (but would be extremely rare) that an electron turns into a positron by catching two W+ bosons in a row: the first W+ would turn the electron into a neutrino (this is standard physics), the neutrino being the same as an antineutrino (if they are their own anti-particle which is unknown), and then the antineutrino turning into a positron by catching another W+ boson, which is again standard physics.

The reverse process can then happen if a positron catches two W- bosons. The W bosons might come from atoms in the vicinity and change one type of nucleus into another in the course of this exchange, but as I said this would be an incredibly rare occurrence.

A closely related physical process called "neutrinoless double beta decay" is actually currently being searched for, precisely in order to prove that neutrinos indeed are their own antiparticles.

As vorlon says, you can always *make* positrons by smashing an electron into something with enough energy or vice versa, but I didn't exactly count that as changing the electron into a positron, which I interpret as having an identifiable particle which gets turned from one in the other by some influence.