This is Neutron decay:
$$n^o \to p^+ + e^- + \overline {\nu_e}.$$
and this is proton one:
$$p^+ \to n^o + e^+ +  \nu_e$$

so when the  $e^+ =e^-$ and  $\nu_e=\overline {\nu_e}$ why n $\not= p$?

**my idea is that:**

 $$\nu_e \not= \overline {\nu_e}$$