Neutrino reconstruction with topological information

In general a decay with a missing (not detected) particle cannot 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 B s 0 mesons is considered as an example to illustrate this method and to compare its performance against conventional approaches.