# Relative Mean lifetime of decays

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## Main Question or Discussion Point

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)?

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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.