We propose a new dihedral angle observable to measure the CP property of the interaction of top quark and Higgs boson in the $tbar{t}H$ production at the 14~TeV LHC. We consider two decay modes of the Higgs boson, $Hto bbar{b}$ and $Hto gammagamma$ and show that the dihedral angle distribution is able to distinguish the CP-even and the CP-odd hypothesis at 95% confidence level with an integrated luminosity of $sim 180~{rm fb}^{-1}$.
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