Measurement of Top Quark Polarization in Top-Antitop Events from Proton-Proton Collisions at<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msqrt><mml:mi>s</mml:mi></mml:msqrt><mml:mo mathvariant="bold">=</mml:mo><mml:mn>7</mml:mn><mml:mtext> </mml:mtext><mml:mtext> </mml:mtext><mml:mi>TeV</mml:mi></mml:math>Using the ATLAS Detector

This Letter presents measurements of the polarization of the top quark in top-antitop quark pair events, using $4.7\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of proton-proton collision data recorded with the ATLAS detector at the Large Hadron Collider at $\sqrt{s}=7\text{ }\text{ }\mathrm{TeV}$. Final states containing one or two isolated leptons (electrons or muons) and jets are considered. Two measurements of ${\ensuremath{\alpha}}_{\ensuremath{\ell}}P$, the product of the leptonic spin-analyzing power and the top quark polarization, are performed assuming that the polarization is introduced by either a $CP$ conserving or a maximally $CP$ violating production process. The measurements obtained, ${\ensuremath{\alpha}}_{\ensuremath{\ell}}{P}_{\mathrm{CPC}}=\ensuremath{-}0.035\ifmmode\pm\else\textpm\fi{}0.014(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.037(\mathrm{syst})$ and ${\ensuremath{\alpha}}_{\ensuremath{\ell}}{P}_{\mathrm{CPV}}=0.020\ifmmode\pm\else\textpm\fi{}0.016(\mathrm{stat}{)}_{\ensuremath{-}0.017}^{+0.013}(\mathrm{syst})$, are in good agreement with the standard model prediction of negligible top quark polarization.

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