Evidence for spin correlation in tt̅ production

Abstract

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 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.