Minimal Kinematic Constraints and MT2

TL;DR

This paper explores the relationship between the MT2 variable and minimal kinematic constraints for mass determination in collider events with missing particles, providing new insights and an improved calculation method.

Contribution

It clarifies how MT2 relates to minimal kinematic constraints and introduces a more efficient algorithm for its computation.

Findings

MT2 is the boundary of the mass region consistent with minimal constraints.

A more efficient algorithm for calculating MT2 is developed.

Additional constraints can lead to more sophisticated mass determination methods.

Abstract

We clarify the relation between the variable MT2 and the method of kinematic constraints, both of which can be used for mass determination in events with two missing (dark matter) particles at hadron colliders. We identify a set of minimal kinematic constraints, including the mass shell conditions for the missing particles and their mother particles, as well as the constraint from the measured missing transverse momentum. We show that MT2 is the boundary of the mass region consistent with the minimal constraints. From this point of view, we also obtained a more efficient algorithm for calculating MT2. When more constraints are available in the events, we can develop more sophisticated mass determination methods starting from the MT2 constraint. In particular, we discuss cases when each decay chain contains two visible particles.