Disentangling Higgs-Top Couplings in Associated Production

In the presence of CP violation, the Higgs-top coupling may have both scalar and pseudoscalar components, $κ_t$ and ${\tilde κ_t}$, which are bounded indirectly but only weakly by the present experimental constraints on the Higgs-gluon-gluon and Higgs-$γ$-$γ$ couplings, whereas upper limits on electric dipole moments provide strong additional indirect constraints on ${\tilde κ_t}$, if the Higgs-electron coupling is similar to that in the Standard Model and there are no cancellations with other contributions. We discuss methods to measure directly the scalar and pseudoscalar Higgs-top couplings by measurements of Higgs production in association with ${\bar t} t$, single $t$ and single ${\bar t}$ at the LHC. Measurements of the total cross sections are very sensitive to variations in the Higgs-top couplings that are consistent with the present indirect constraints, as are invariant mass distributions in ${\bar t} t H$, $tH$ and ${\bar t} H$ final states. We also investigate the additional information on $κ_t$ and ${\tilde κ_t}$ that could be obtained from measurements of the longitudinal and transverse $t$ polarization in the different associated production channels, and the ${\bar t} t$ spin correlation in ${\bar t} t H$ events.

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