# A general method for determining the masses of semi-invisibly decaying particles at hadron colliders

## TL;DR

This paper introduces a new general method using transverse kinematic variables to accurately determine the masses of semi-invisibly decaying particles at hadron colliders, demonstrated with LHC dilepton top quark events.

## Contribution

The paper develops analytical formulas and new variables for mass determination, providing a universal approach applicable to various semi-invisible decay scenarios.

## Key findings

- Masses can be extracted from endpoint measurements of $M_{CT_ot}$ and $D_{CT}$.
- Derived formulas define boundaries of kinematic regions in variable planes.
- Method successfully applied to dilepton $t\bar{t}$ events at the LHC.

## Abstract

We present a general solution to the long standing problem of determining the masses of pair-produced, semi-invisibly decaying particles at hadron colliders. We define two new transverse kinematic variables, $M_{CT_\perp}$ and $M_{CT_\parallel}$, which are suitable one-dimensional projections of the contransverse mass $M_{CT}$. We derive analytical formulas for the boundaries of the kinematically allowed regions in the $(M_{CT_\perp},M_{CT_\parallel})$ and $(M_{CT_\perp},M_{CT})$ parameter planes, and introduce suitable variables $D_{CT_\parallel}$ and $D_{CT}$ to measure the distance to those boundaries on an event per event basis. We show that the masses can be reliably extracted from the endpoint measurements of $M_{CT_\perp}^{max}$ and $D_{CT}^{min}$ (or $D_{CT_\parallel}^{min}$). We illustrate our method with dilepton $t\bar{t}$ events at the LHC.