Generalised Known Kinematics (GKK): an approach for kinematic observables in pair production events with decays involving invisible particles

Missing kinematic information of known invisible particles, such as neutrinos, limit several high-energy physics analysis. The undetected particle carries away momentum and energy information, preventing the total reconstruction of such an event. This paper presents a new method to handle this missing information, referred to as the Generalised Known Kinematics (GKK) approach. Its event-by-event probability density distributions that describe the physically allowed kinematics of an event. For GKK, we consider the available kinematic information and constraints given by the assumed final state. Summing these event-wise distributions over large data sets allows the determination of parameters that influence the event kinematics. Examples are particle masses obscured by the missing information on the invisible final-state particles. The method is demonstrated in simulation studies with τ+τ− events in e+e− collisions at the Υ (4S) resonance, presenting a new, promising approach for measuring the τ lepton mass.