# Timing information at HL-LHC: Complete determination of masses of Dark Matter and Long lived particle

## TL;DR

This paper demonstrates that precise timing measurements at the HL-LHC can fully determine the masses of dark matter particles and long-lived particles in collider events, solving a longstanding kinematic problem.

## Contribution

It introduces a method to use timing information at HL-LHC to completely solve for the masses of invisible and long-lived particles in collider events.

## Key findings

- Timing measurements enable full mass determination of invisible particles.
- The method applies to long-lived particles with displaced vertices.
- It provides a new approach for dark matter searches at colliders.

## Abstract

A long standing problem in kinematics at the hadron colliders is to determine the mass of invisible particles. This issue is particularly important for the signals of dark matter, which becomes one of the prominent targets of future collider experiments. In this paper, we show that the additional information from the precise timing measurement, which will be available at the planned high-liminosity run of the LHC (HL-LHC), will shade new light on the kinematics study. As a concrete example, we focus on the signal of the pair produced long-lived particles ($LLP_{1,2}$), respectively leaving displaced vertex with visible ($V_{1,2}$) and invisible ($I_{1,2}$) final state, $pp \to LLP_1+LLP_2 \to (V_1+I_1)+(V_2+I_2)$. We explicitly show that this system is completely solvable with timing information.