A set of new observables in the process $e^+_{}e^-_{}\to ZHH$

TL;DR

This paper introduces nine new measurable angular observables in the process e+e- to ZHH, which are sensitive to non-standard Higgs couplings and can improve the understanding of Higgs interactions beyond total cross section measurements.

Contribution

It derives an analytic expression for differential cross sections with nine new observables, analyzing their symmetry properties and dependence on effective Higgs couplings, including polarization effects.

Findings

New observables depend on most effective Lagrangian parameters.

Observables provide complementary information to total cross section.

Longitudinal polarization enhances sensitivity to Higgs couplings.

Abstract

Consequences of non-standard Higgs couplings in the final-state distributions of the process $e^+_{}e^-_{} \to ZHH$ are studied. We derive an analytic expression for the differential cross section, which has in the most general case 9 non-zero functions. These functions are the coefficients of 9 angular terms, depend on the Higgs couplings, and can be experimentally measured as observables. Symmetry properties of these 9 functions are carefully discussed, and they are divided into 4 categories under CP and $\mathrm{CP\tilde{T}}$. The relations between our observables and the observables which exist in the literature are also clarified. We numerically study the dependence of our observables on the parameters in an effective Lagrangian for the Higgs couplings. It is shown that these new observables depend on most of the effective Lagrangian parameters in different ways from the total cross section. A benefit from longitudinally polarized $e^+_{}e^-_{}$ beams is also discussed.