  In the framework of the supersymmetric standard model, the lighter stau often
becomes long-lived. Such longevity of the stau is realized in three
well-motivated scenarios: (A) the stau is the next-to-lightest supersymmetric
particle (NLSP) and the gravitino is the lightest supersymmetric particle
(LSP), (B) the stau is the LSP and R-parity is slightly violated, and (C) the
stau is NLSP, the neutralino is the LSP, and the their masses are degenerate.
We study the event topology and the decay of the stopping stau at the hadron
calorimeter at the LHC, and show that it is possible to identify the reason why
the stau becomes long-lived.
