Higgs decays to four leptons to $ \mathcal{O}\left(1/{\Lambda}^4\right) $ in SMEFT

A bstract: We study the decays $$ h\to \ell \overline{\ell}\left(Z\to {\ell}^{\prime }{\overline{\ell}}^{\prime}\right) $$ h → ℓ ℓ ¯ Z → ℓ ′ ℓ ¯ ′ and $$ h\to \ell {\overline{\nu}}_{\ell }{\nu}_{\ell^{\prime }}{\overline{\ell}}^{\prime } $$ h → ℓ ν ¯ ℓ ν ℓ ′ ℓ ¯ ′ within the SMEFT framework and including effects up to $$ \mathcal{O}\left(1/{\Lambda}^4\right) $$ O 1 / Λ 4 , where Λ 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 $$ \mathcal{O}\left(1/{\Lambda}^4\right) $$ O 1 / Λ 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 $$ h\to \ell \overline{\ell}\left(Z\to {\ell}^{\prime }{\overline{\ell}}^{\prime}\right) $$ h → ℓ ℓ ¯ Z → ℓ ′ ℓ ¯ ′ . For $$ h\to \ell {\overline{\nu}}_{\ell }{\nu}_{\ell^{\prime }}{\overline{\ell}}^{\prime } $$ h → ℓ ν ¯ ℓ ν ℓ ′ ℓ ¯ ′ , new angular dependencies do arise at $$ \mathcal{O}\left(1/{\Lambda}^4\right) $$ O 1 / Λ 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 $$ \ell {\overline{\nu}}_{\ell }{\nu}_{\ell^{\prime }}{\overline{\ell}}^{\prime } $$ ℓ ν ¯ ℓ ν ℓ ′ ℓ ¯ ′ , we must study Higgs production and decay together with the appropriate observables, which we find obscures the new angular effects.