Reducing combinatorial uncertainties: A new technique based on MT2 variables

TL;DR

This paper introduces a new technique using MT2 variables to resolve combinatorial ambiguities in collider events with invisible particles, improving accuracy in identifying correct particle combinations.

Contribution

The authors develop a novel method based on MT2 and on-shell reconstruction to systematically enhance combinatorial resolution in collider analyses, applicable to new physics scenarios.

Findings

Improved accuracy in correct particle combination identification.

Method effectively applied to top-antitop decay events.

Potential applicability to dark matter candidate searches.

Abstract

We propose a new method to resolve combinatorial ambiguities in hadron collider events involving two invisible particles in the final state. This method is based on the kinematic variable MT2 and on the MT2-assisted-on-shell reconstruction of invisible momenta, that are reformulated as `test' variables Ti of the correct combination against the incorrect ones. We show how the efficiency of the single Ti in providing the correct answer can be systematically improved by combining the different Ti and/or by introducing cuts on suitable, combination-insensitive kinematic variables. We illustrate our whole approach in the specific example of top anti-top production, followed by a leptonic decay of the W on both sides. However, by construction, our method is also directly applicable to many topologies of interest for new physics, in particular events producing a pair of undetected particles, that are potential dark-matter candidates. We finally emphasize that our method is apt to several generalizations, that we outline in the last sections of the paper.