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.
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If you start with a proton and an anti-proton, the initial baryon number is zero, so there is no problem with ending up in a state with zero baryon number such as an electron and positron. According to wikipedia, typically mesons are an intermediate product in such a reaction, and you may also produce photons and neutrinos.
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$\begingroup$ Interesting. In my original question I've talked about completely converting protons to electrons, so this means, this would only be possible, if, in a closed system, you'd have an equal number of particles and antiparticles? $\endgroup$– Mat NXCommented Oct 30, 2020 at 23:02
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$\begingroup$ 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). $\endgroup$– AndrewCommented Oct 31, 2020 at 1:17
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$\begingroup$ In general you have to look up (or know) the baryon number for all the particles in the initial and final state, sum them up, and compare. $\endgroup$– AndrewCommented Oct 31, 2020 at 1:29