  We propose a simple way to extract particle masses given a displaced vertex
signature in event topologies where two long-lived mother particles decay to
visible particles and an invisible daughter. The mother could be either charged
or neutral and the neutral daughter could correspond to a dark matter particle
in different models. The method allows to extract the parent and daughter
masses by using on-shell conditions and energy-momentum conservation, in
addition to the displaced decay positions of the parents, which allows to solve
the kinematic equations fully on an event-by-event basis. We show the validity
of the method by means of simulations including detector effects. If displaced
events are seen in discovery searches at the Large Hadron Collider (LHC), this
technique can be applied.
