Measuring Top-Quark Polarization in Top-Pair + Missing Energy Events

TL;DR

This paper introduces a new method to measure top-quark polarization using the charged lepton energy fraction, which is sensitive to new physics and robust against measurement uncertainties, demonstrated through simulation of supersymmetric top squark events.

Contribution

A novel approach based on lepton energy ratios for measuring top-quark polarization, applicable in top-pair plus missing energy events, with detailed simulation validation.

Findings

Lepton energy ratio is highly sensitive to top-quark polarization.

Method is insensitive to precise top-quark energy measurement.

Effective in supersymmetric top squark pair production scenarios.

Abstract

The polarization of a top-quark can be sensitive to new physics beyond the standard model. We propose a novel method to measure top-quark polarization, based on the charged lepton energy fraction in top-quark decay, and illustrate the method with a detailed simulation of top-quark pairs produced in supersymmetric top squark pair production. We show that the lepton energy ratio distribution that we define is very sensitive to the top-quark polarization but insensitive to the precise measurement of the top-quark energy.