# I Relative Mean lifetime of decays

1. Jun 21, 2016

### Xico Sim

Hi there.

I want to compare the mean lifetimes of two particles which decay in a way given by two known reaction formulas, such as

$\rho^0 \rightarrow \pi^+ + \pi^-$ and $\Xi^- \rightarrow \Lambda^0 + \pi^-$

In this case it's easy: since the first one corresponds to a first interaction and the second one to a weak interaction, the first one has a shorter mean lifetime. If, for instance, both were weak, could we still compare the lifetimes (using the particles mass, for example)?

2. Jun 21, 2016

### Staff: Mentor

You can always calculate the lifetime with QFT. If two decays are similar, there might be rules to compare them without a full calculation, but that depends on the specific situation then. The two examples you have here are completely different.