Measuring massive metastable charged particles with ATLAS RPC timing information.

We investigate the measurement of massive metastable charged particles in ATLAS, using timing information from the resistive plate chambers (RPCs). As representative particle candidates we use staus, the partners of $ au$ leptons in supersymmetric models with gravitino dark matter (GDM), which may well be stable on the scale of the detector. The generic signatures of massive metastable charged particles are a long Time-of-Flight (ToF) and high energy-loss ($dE/dx$). The RPC timing information allows us to measure the ToF of a particle which, taken in conjunction with the measurement of the particle's momentum from its track, allows one to determine its mass. We pioneer the study of the RPCs' potential for this measurement. We also consider triggering effects on the event selection, and discuss quantitatively the ATLAS potential for measuring the stau mass in three specific GDM benchmark scenarios.