  Supersymmetry (SUSY) with a long-lived stau is an attractive scenario in the
LHC experiments because one can directly observe stau tracks in each SUSY
event, and thus precise measurements of SUSY particle masses are possible. In
this scenario, we discuss the possibility to observe/measure parity violation
in interactions among SUSY particles. Such a measurement will be important in
determining spins and chiralities of SUSY particles. We use the last step of
the cascade-decay chain: $\chi^0\to\tilde\tau\tau\to\tilde\tau(l\nu\bar\nu)$,
where the polarization of the tau lepton can be determined statistically by
looking at the energy distribution of the final state lepton. Comparing with
the theoretical formula of the neutralino differential decay width, one can
extract the size of parity violation in the interaction vertices among the
stau, the tau lepton and the neutralino. We perform a Monte Carlo simulation to
see if the effect is visible at the LHC experiments.
