  It is often true that an invariant mass constructed from visible decay
products of a heavy particle may attain a maximum(or minimum) for a certain
kinematic configuration only -- this fact can be used to reconstruct relevant
particle masses from observed decay product momenta of events near the
invariant mass endpoint. MSSM neutralino and chargino mass reconstruction at
the LHC from multi-lepton endstates is illustrated by way of example.
