ttbar Spin Correlations at D0

TL;DR

This paper reports on the measurement of top-antitop quark spin correlations at D0, using angular and matrix-element techniques, providing the first evidence of non-zero spin correlations in ttbar events.

Contribution

It introduces a matrix-element based analysis method for ttbar spin correlations and presents the first evidence of non-vanishing correlations at D0.

Findings

First evidence for non-zero ttbar spin correlations.

Application of matrix-element technique to dilepton and semileptonic channels.

Measurement consistent with Standard Model predictions.

Abstract

The heaviest known elementary particle today, the top quark, has been discovered in 1995 by the CDF and D0 collaborations at the Tevatron collider at Fermilab. Its high mass and short lifetime, shorter than the timescale for hadronization, makes the top quark a special particle to study. Due to the short lifetime, the top quark's spin information is preserved in the decay products. In this article we discuss the studies of ttbar spin correlations at D0, testing the full chain from production to decay. In particular, we present a measurement using angular information and an analysis using a matrix-element based technique. The application of the matrix-element based technique to the ttbar dilepton and semileponic final state resulted in the first evidence for non-vanishing ttbar spin correlations.