  Many analyses in high energy physics are limited due to missing kinematic
information of known invisible particles in the detector, for example
neutrinos. The undetected particle carries away momentum and energy
information, preventing the full reconstruction of such an event. In this
paper, we present a method to handle this missing information, referred to as
the Generalised Known Kinematics (GKK) approach. It is based on constructing
event-by-event probability density distributions that describe the physically
allowed kinematics of an event. For GKK we take into account 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, such as particle masses, which
are otherwise obscured by the missing information on the invisible final-state
particles. The method is demonstrated in simulation studies with $\tau^+
\tau^-$ events in $e^+ e^-$ collisions at the $\Upsilon$(4S) resonance,
presenting a new, promising approach for the measurement of the $\tau$ lepton
mass.
