Making The Most Of MET: Mass Reconstruction From Collimated Decays

TL;DR

This paper presents a method to improve mass reconstruction of invisible particles at hadron colliders by decomposing MET into expected contributions, especially effective when particles are light and aligned with visible objects, aiding in identifying particle masses.

Contribution

The paper introduces a novel approach to decompose MET into full four-momenta of invisible particles using prior kinematic assumptions, enhancing mass reconstruction accuracy in collider experiments.

Findings

Effective mass peak reconstruction demonstrated for boosted neutralinos.

Method improves mass resolution in scenarios with aligned invisible and visible particles.

Applicable to supersymmetry models with light, boosted neutralinos.

Abstract

At hadron colliders invisible particles $\chi$ can be inferred only through observation of the transverse component of the vectorial sum of their momenta -- missing $E_T$ or MET -- preventing reconstruction of the masses of their mother particles. Here we outline situations where prior prejudice about the event kinematics allows one to make the most of MET by decomposing it into its expected sum of transverse contributions, each of which may be promoted to a full four-momentum approximating the associated $\chi$. Such prejudice arises when all $\chi$ in the event are expected to be light and (anti-)parallel to a visible object, due to spin-correlations, back-to-back decays or boosted decays. We focus on the last of these, with boosted semi-invisibly decaying neutralinos widely motivated in supersymmetry (in the presence of light gravitinos, singlinos, photini or pseudo-goldstini), and demonstrate our simple method's ability to reconstruct sharp mass peaks from the MET decomposition.