Date of this Version
PHYSICAL REVIEW LETTERS 108, 032004 (2012); DOI: 10.1103/PhysRevLett.108.032004
We present a measurement of the ratio of events with correlated t and t̅ spins to the total number of tt̅ events. This ratio f is evaluated using a matrix-element-based approach in 729 tt̅ candidate events with a single lepton ℓ (electron or muon) and at least four jets. The analyzed pp̅ collisions data correspond to an integrated luminosity of 5.3 fb-1 and were collected with the D0 detector at the Fermilab Tevatron collider operating at a center-of-mass energy √s = 1.96 TeV. Combining this result with a recent measurement of f in dileptonic final states, we find f in agreement with the standard model. In addition, the combination provides evidence for the presence of spin correlation in tt̅ events with a significance of more than 3 standard deviations.