# Tau momentum for decay length

1. Jun 1, 2015

### ChrisVer

Hi,
I'm looking for the momentum so that the decay length of a tau (mean lifetime $t_{lft}=2.9 \times 10^{-13}s$) can be $2mm$.
I was wondering whether someone can use the formula I got:

$l_{lab}= t_{lab} u = \gamma u t_{lft} \Rightarrow pc= m \gamma u = m \frac{l_{lab}}{t_{lft}}$?

(Looking just for a confirmation)

2. Jun 1, 2015

### Orodruin

Staff Emeritus
Looks reasonable.