The measurement of the $$H ightarrow au au $$H→ττ signal strength in the future $$e^{+}e^{-}$$e+e- Higgs factories

The Circular Electron Positron Collider and the International Linear Collider are two electron-positron Higgs factories. They are designed to operate at a center-of-mass energy of 240 and 250 GeV and accumulate 5.6 and 2 $$ab^{-1}$$ of integrated luminosity. This paper estimates their performance on the $$H ightarrow au ^{+} au ^{-}$$ benchmark measurement. Using the full simulation analysis, the CEPC is expected to measure the signal strength to a relative accuracy of 0.8%. Extrapolating to the ILC setup, we conclude the ILC can reach a relative accuracy of 1.1% or 1.2%, corresponding to two benchmark beam polarization setups. The physics requirement on the mass resolution of the Higgs boson with hadronic decay final states is also discussed, showing that the CEPC baseline design and reconstruction fulfill the accuracy requirement of the $$H ightarrow au ^{+} au ^{-}$$ signal strength.