Question

Using the conservation of baryon number, charge and lepton number, decide if the following reaction is possible:

a) n→p+e^-

Answer 1

The reaction

$$n→p+e^-$$

is not possible because, although the charge and baryon numbers are conserved, the lepton numbers of neutron and proton are 0, while it is 1 for electrons. Therefore, for such a reaction to happen, we need one anti-electron neutrino with lepton number of -1:

$$n→p+e^-+\bar{\nu}_e.$$