Measurement of ttbar Spin Correlation in ppbar Collisions Using the CDF II Detector at the Tevatron

TL;DR

This paper measures the spin correlation of top-antitop quark pairs in proton-antiproton collisions at the Tevatron, testing QCD predictions and probing for new physics effects.

Contribution

First measurement of ttbar spin correlation in ppbar collisions at Tevatron using the CDF II detector in the lepton plus jets channel.

Findings

Measured spin correlation coefficient kappa = 0.60 +/- 0.50 (stat) +/- 0.16 (syst)

Result consistent with QCD prediction of kappa ≈ 0.40

Uses 1001 candidate events at sqrt(s) = 1.96 TeV

Abstract

The ttbar spin correlation at production is a fundamental prediction of QCD and a potentially incisive test of new physics coupled to top quarks. We measure the ttbar spin state in ppbar collisions at sqrt(s) = 1.96 TeV using 1001 candidate events in the lepton plus jets decay channel reconstructed in the CDF II detector. In the helicity basis, for a top-quark mass of 172.5 GeV/c^2, we find a spin correlation coefficient kappa = 0.60 +/- 0.50 (stat) +/- 0.16 (syst), consistent with the QCD prediction, kappa ~= 0.40.