Constraining Higgs boson effective couplings at electron-positron colliders

We probe the dimension-six operators contributing to Higgs production in association with a $Z$ boson at the future high-luminosity electron-positron colliders. Potential constraints on dimension-six operators in the Higgs sector are determined by performing a shape analysis on the differential angular distribution of the Higgs and $Z$ boson decay products. The analysis is performed at the center-of-mass energies of 350 and 500 GeV including a realistic detector simulation and the main sources of background processes. The 68% and 95% confidence level upper limits are obtained on the contributing anomalous couplings considering only the decay of the Higgs boson into a pair of b-quarks and leptonic $Z$ boson decay. Our results show that angular observables provide a great sensitivity to the anomalous couplings, in particular, at the high-luminosity regime.

Figure 1

Representative tree level Feynman diagrams for the production of a Higgs boson in association with a $Z$ boson at an electron-positron collider in the presence of dimension-six operators.

Figure 2

The transverse momentum and pseudorapidity, and mass distributions of the reconstructed $Z({\ell }^{+}{\ell }^{-})$ and Higgs boson ($b\overline{b}$) for particular values of ${\overline{c}}_H=0.1$, ${\overline{c}}_{\gamma }=0.1$ and SM background processes. The distributions are depicted after the preselection cuts.

Figure 3

The $\cos (\ell ,b-\text{jets})$ distributions for SM production of the Higgs boson in association with a $Z$ boson and $H+Z$ production in the present various couplings at the center-of-mass energy of $\sqrt{s}=500\mathrm{GeV}$. The distributions are depicted after the preselection cuts. The signal distributions are presented for particular values of the coupling set to 0.1. The distributions of two main background processes $t\overline{t}$ and $ZZ$ are depicted for more illustration. The uncertainty on the SM $H+Z$ production is only the statistical uncertainty corresponding to the integrated luminosity of $300{\mathrm{fb}}^{-1}$.

Figure 4

Contours of 68% and 95% confidence level obtained from a fit using the $\cos (\ell ,b-\text{jets})$ distributions for $\sqrt{s}=350\mathrm{GeV}$ with a luminosity of $300{\mathrm{fb}}^{-1}$.

Figure 5

Contours of 68% and 95% confidence level obtained from a fit using the $\cos (\ell ,b-\text{jets})$ distributions for $\sqrt{s}=350\mathrm{GeV}$ with an integrated luminosity of $3{\text{ab}}^{-1}$.

Figure 6

Contours of 68% and 95% confidence level obtained from a fit using the $\cos (\ell ,b-\text{jets})$ distributions for the center-of-mass energy of $\sqrt{s}=500\mathrm{GeV}$ with an integrated luminosity of $300{\mathrm{fb}}^{-1}$.