A measurement of the correlations between the polar angles of leptons from the decay of pair-produced $t$ and $\overline{t}$ quarks in the helicity basis is reported, using proton-proton collision data collected by the ATLAS detector at the LHC. The dataset corresponds to an integrated luminosity of $4.6{\mathrm{fb}}^{-1}$ at a center-of-mass energy of $\sqrt{s}=7\mathrm{TeV}$ collected during 2011. Candidate events are selected in the dilepton topology with large missing transverse momentum and at least two jets. The angles ${\theta }_1$ and ${\theta }_2$ between the charged leptons and the direction of motion of the parent quarks in the $t\overline{t}$ rest frame are sensitive to the spin information, and the distribution of $\cos {\theta }_1·\cos {\theta }_2$ is sensitive to the spin correlation between the $t$ and $\overline{t}$ quarks. The distribution is unfolded to parton level and compared to the next-to-leading order prediction. A good agreement is observed.

• Received 27 October 2015

DOI:https://doi.org/10.1103/PhysRevD.93.012002

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© 2016 CERN, for the ATLAS Collaboration