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by ellis-bell 1558 days ago
lepton number does not need to be conserved. it is an approximate symmetry of nature. if lepton number were conserved, neutrinos could not oscillate.

quarks, the particles composing protons and neutrons, have fractional charge; these would be the particles that would interact with an electron or positron. the charges wouldn't work out (charge is conserved (as far as we known...)) so there wouldn't be a fundamental electromagnetic interaction between a single quark and a e+/e- (i.e., an annihilation). But there are fundamental weak interactions between quarks and e+/e-; these processes are known as inverse beta decay and are used for pet scans.
2 comments
lanstin 1558 days ago
To quote Wikipedia: “Lepton flavor is only approximately conserved, and is notably not conserved in neutrino oscillation.[6] However, total lepton number is still conserved in the Standard Model.“

The beta decay gives rise to e.g. a positron and a neutrino (or an electron and an anti-neutrino).

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floxy 1558 days ago
What is going on in neutron stars? The layman's answer is that the electrons get squeezed into the protons due to the extreme gravity, leaving only neutrons. But I suppose (?) there needs to be a anti-neutrino or similar that comes along to "complete" the reaction?

Edit: I guess it is inverse beta decay:

https://en.wikipedia.org/wiki/Inverse_beta_decay#Electron_in...

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db48x 1558 days ago
As a rule of thumb it’s good enough for most particle interactions.
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