We study the decays $h \to \ell \bar{ \ell} \left(Z \to \ell' \bar{ \ell'}\right)$ and $h\to\ell\bar{ \nu}_\ell\nu_{ \ell'}\bar{ \ell'}$ within the SMEFT framework and including effects up to $\mathcal O(1/\Lambda^4)$, where $\Lambda$ is the new physics scale suppressing higher dimensional operators. To work to this order, we must include the square of dimension-six operators and the interference of dimension-eight operators with the Standard Model. We study angular asymmetries and other differential decay observables and determine which are most sensitive to $\mathcal O(1/\Lambda^4)$ effects. While new kinematic structures arising in higher dimensional operators have the potential to induce novel angular dependency, we find this does not occur for $h\to\ell\bar{ \ell}\left(Z\xrightarrow{ }\ell'\bar{ \ell'}\right)$. For $h \to \ell \bar{ \nu}_\ell \nu_{ \ell'} \bar{ \ell'}$, new angular dependencies do arise at $\mathcal O(1/\Lambda^4)$, though they require a fully reconstructible (meaning we can go to the Higgs rest frame) final state. For non-reconstructible final states such as $\ell \bar{ \nu}_\ell \nu_{ \ell'} \bar{ \ell'}$, we must study Higgs production and decay together with the appropriate observables, which we find obscures the new angular effects.
Categories: hep-ph