title: Measuring top-quark polarization in top-pair + missing-energy events.
abstract: The polarization of a top quark can be sensitive to new physics beyond the standard model. Since the charged lepton from top-quark decay is maximally correlated with the top-quark spin, it is common to measure the polarization from the distribution in the angle between the charged lepton and the top-quark directions. We propose a novel method based on the charged lepton energy fraction 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.
authors.affiliation: High Energy Physics Division, Argonne National Laboratory, Argonne, Illinois 60439, USA.
authors.forename: Edmond L
authors.initials: EL
authors.lastname: Berger
authors.forename: Qing-Hong
authors.initials: QH
authors.lastname: Cao
authors.forename: Jiang-Hao
authors.initials: JH
authors.lastname: Yu
authors.forename: Hao
authors.initials: H
authors.lastname: Zhang