Beyond Higgs Couplings: Probing the Higgs with Angular Observables at Future $e^{+}{e}^{-}$ Colliders

Abstract

We study angular observables in the $e^{+}{e}^{-}\to ZH\to {\ell }^{+}{\ell }^{-}b\bar{b}$ channel at future circular $e^{+}{e}^{-}$ colliders such as CEPC and FCC-ee. Taking into account the impact of realistic cut acceptance and detector effects, we forecast the precision of six angular asymmetries at CEPC (FCC-ee) with center-of-mass energy $\sqrt{s}=$ 240 GeV and 5 (30) ${\mathrm{ab}}^{-1}$ integrated luminosity. We then determine the projected sensitivity to a range of operators relevant for the Higgs-strahlung process in the dimension-6 Higgs EFT. Our results show that angular observables provide complementary sensitivity to rate measurements when constraining various tensor structures arising from new physics. We further find that angular asymmetries provide a novel means of both probing BSM corrections to the $HZ{\hat{I}}^3$ coupling and constraining the "blind spot" in indirect limits on supersymmetric scalar top partners.

28 pages, 9 figures. v2: references added, matches published version in JHEP