Secondary vertex

A secondary vertex is a point in space where an unstable particle produced in a collision decays to other particles. Experimentally, secondary vertices can only be reconstructed for particles that are sufficiently long-lived to travel a resolvable distance in the detector before decaying. In addition, the primary particle must decay to at least one charged particle, in practice often to at least two, so that their tracks can be reconstructed and the secondary vertex position determined from them.