# Is the baryon number consistent when it comes to annihilation?

I've previously asked a question on here about if it was possible to change the barion number by radioactive decay, for example positron emission, and the answer was of course no, as the baryon number rmains consistent. I've also talked about this problem with some friends, and one of them came up with a process to turn baryonic matter into purely energy or leptons. Basically, their idea was, that, at first, a proton and an antiproton should annihilate each other, which should only leave energy, and the resulting photons should then, by the mechanism of pair production create an electron and a positron. Of course, to an amateur like me, this makes sense. But, as Baryon number is supposed to be consistent, this shouldn't work? Can someone explain why or why not this works? It would be greatly apreciated.

• The general rule of thumb is that "anything not forbidden is mandatory." In other words, a reaction is usually allowed to happen unless there's a symmetry (or equivalently a conservation rule) that forbids it. Focusing just on baryon number, a reaction $p^+ p^- \rightarrow e^+ e^-$ is allowed since the initial and final baryon number are zero. On the other hand, a reaction $p^+ \rightarrow e^+$ is not allowed, since the baryon number goes from 1 to 0. (There are also other things wrong with this reaction but we are just focused on baryon number). Oct 31 '20 at 1:17