# Weak decay - cross sections

1. Jul 14, 2010

### zakk87

Weak decay -- cross sections

I have to estimate the ratio between the cross sections of the following weak processes:

$$\nu_{\mu} + e^{-} \Rightarrow \nu_{e} + \mu^{-}$$
$$\bar{\nu_{e}} + e^{-} \Rightarrow \bar{\nu_{\mu}} + \mu^{-}$$

My teacher says that as the first process is $$LL \Rightarrow LL$$ (i.e. chirality of the initial and final states) and the second process is $$LR \Rightarrow LR$$, when can immediately conclude that, the ratio between the cross sections is 3:1 (provided that the incoming neutrinos energies are the same).

I cannot understand why he jumps to that conclusion.