Generalised Known Kinematics (GKK) An Approach for Kinematic Observables in Pair Production Events with Decays Involving Invisible Particles

TL;DR

The paper introduces the Generalised Known Kinematics (GKK) method, which constructs event-by-event probability distributions to infer parameters like particle masses in events with missing invisible particles, demonstrated with tau lepton mass measurement.

Contribution

It presents a novel GKK approach that utilizes event-wise probability densities to extract kinematic parameters in the presence of missing information, improving analysis of pair production events.

Findings

Effective in simulation studies of tau pair events

Enables mass measurement despite missing neutrino information

Offers a new tool for high energy physics analyses

Abstract

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.