Neutrino reconstruction with topological information
  In general a decay with a missing (not detected) particle can not be fully reconstructed apart from a few exceptions. For example, if the momentum of the decaying particle is known or if the missing energy in an event is measured precisely, then the missing particle 4-momentum can be determined. Here a new method is proposed that utilizes additional information about the topology of a decay: The direction from the primary to the secondary vertex combined with momentum conservation allows the determination of the missing particle momentum up to a twofold ambiguity. The semileptonic decay of the Bs mesons is considered as an example to illustrate this method and to compare its performance against conventional approaches. 
S. Dambach, U. Langenegger, A. Starodumov