Potential Precision on Higgs Couplings and Total Width at the ILC

Understand

We outline a systematic approach to the determination of the Standard Model-like Higgs boson total width and measurable coupling parameters in a model-independent manner at the International Linear Collider (ILC) and illustrate the complementarity for operating the ILC at $250$ GeV near the $Zh$ threshold and at $500$ GeV and $1$ TeV utilizing the $WW, ZZ$ fusion processes.

• We perform detailed simulations for an important contributing channel to the coupling determination and for invisible decays.
• Without model assumptions, and combining the information for the coupling ratios from the LHC, the total width can be determined to an accuracy of about $6%$, and the couplings for the observable channels can be measured to the $(3-5)%$ level at 250 GeV, reaching $(1-3)%$ level including the 500 GeV results, with further improvements possible with a $1$ TeV run.
• The best precision for the branching fraction measurement of the Higgs to invisible modes can be reached at $0.5-0.7%$ around the $Zh$ threshold.