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The tt̄ 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 tt̄ spin state in pp̄ collisions at √s=1.96TeV 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 172.5GeV/c2, we find a spin correlation coefficient κ=0.60±0.50(stat)±0. 16(syst), consistent with the QCD prediction, κ 0.40. © 2011 American Physical Society.

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Physical Review D - Particles, Fields, Gravitation and Cosmology