On measuring the masses of pair-produced semi-invisibly decaying particles at hadron colliders

TL;DR

This paper introduces a new method for measuring the combined masses of pair-produced particles and their invisible decay products at hadron colliders, leveraging Lorentz invariance of transverse momentum components.

Contribution

The paper presents a novel analytical technique that uses Lorentz invariance to determine the masses of both initial and invisible particles in pair-produced decays.

Findings

Technique enables mass measurement despite non-zero visible invariant masses.

Potential to determine both initial and invisible particle masses independently.

Practical application may be limited by ISR jet contamination.

Abstract

A straightforward new technique is introduced which enables measurement at hadron colliders of an analytical combination of the masses of pair-produced semi-invisibly decaying particles and their invisible decay products. The new technique makes use of the invariance under contra-linear Lorentz boosts of a simple combination of the transverse momentum components of the aggregate visible products of each decay chain. In the general case where the invariant masses of the visible decay products are non-zero it is shown that in principle the masses of both the initial particles from the hard scattering and the invisible particles produced in the decay chains can be determined independently. This application is likely to be difficult to realise in practice however due to the contamination of the final state with ISR jets. The technique may be of most use for measurements of SUSY particle masses at the LHC, however the technique should be applicable to any class of hadron collider events in which heavy particles of unknown mass are pair-produced and decay to semi-invisible final states.