Physical Review D 83,3 (2011)
The t (t) over bar 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 t (t) over bar spin state in p (p) over bar collisions at root 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 approximate to 0.40.
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