11.2 Exercise 7

Which of the following decays cannot occur because the law of conservation of lepton number is violated?

$\begin{matrix}\left(\text{a}\right) \text{n} \rightarrow \text{p} + \text{e}^{−} & & & \left(\text{e}\right) \pi^{−} \rightarrow \text{e}^{−} + \left(\overset{−}{\upsilon}\right)_{\text{e}} \\ \left(\text{b}\right) \mu^{+} \rightarrow \text{e}^{+} + \upsilon_{\text{e}} & & & \left(\text{f}\right) \mu^{−} \rightarrow \text{e}^{−} + \left(\overset{−}{\upsilon}\right)_{\text{e}} + \upsilon_{\mu} \\ \left(\text{c}\right) \pi^{+} \rightarrow \text{e}^{+} + \upsilon_{\text{e}} + \overset{−}{\upsilon}_{\mu} & & & \left(\text{g}\right) \Lambda^{0} \rightarrow \pi^{−} + \text{p} \\ \left(\text{d}\right) \text{p} \rightarrow \text{n} + \text{e}^{+} + \upsilon_{\text{e}} & & & \left(\text{h}\right) \text{K}^{+} \rightarrow \mu^{+} + \upsilon_{\mu}\end{matrix}$