ILC Higgs White Paper

TL;DR

The ILC Higgs White Paper presents a comprehensive evaluation of Higgs theory and Higgs-physics program at the International Linear Collider. It outlines how precision measurements of Higgs production, decays, and couplings (via ZH, WW fusion, ttH, and double-Higgs channels) can test the Standard Model, constrain extended Higgs sectors (2HDM, MSSM, NMSSM), and probe new dynamics of electroweak symmetry breaking. A central theme is model-independence: the use of effective Lagrangians and kappa-frameworks to extract absolute Higgs properties, total width, and couplings, while also exploring specific benchmark parameterizations and the impact of new particles in loops. The document also discusses accelerator and detector configurations (ILD, SiD), systematic uncertainties, and the gamma-gamma option, concluding that the ILC can deliver percent-level Higgs-coupling measurements, a robust determination of the Higgs width, and sensitivity to additional Higgs states, thereby offering substantial scientific value beyond LHC capabilities. The work emphasizes the ILC’s role in validating the Higgs mechanism, testing electroweak baryogenesis scenarios via the hhh coupling, and exploring a wide landscape of BSM Higgs sectors through direct production and precision Higgs-vertex studies.

Abstract

The ILC Higgs White Paper is a review of Higgs Boson theory and experiment at the International Linear Collider (ILC). Theory topics include the Standard Model Higgs, the two-Higgs doublet model, alternative approaches to electroweak symmetry breaking, and precision goals for Higgs boson experiments. Experimental topics include the measurement of the Higgs cross section times branching ratio for various Higgs decay modes at ILC center of mass energies of 250, 500, and 1000 GeV, and the extraction of Higgs couplings and the total Higgs width from these measurements. Luminosity scenarios based on the ILC TDR machine design are used throughout. The gamma-gamma collider option at the ILC is also discussed.

Figures (67)

• Figure 1: The Standard Model prediction that the Higgs coupling to each particle is proportional to its mass. Expected precision from the full ILC program for the coupling determination is also shown.
• Figure 2: Branching ratio of the Higgs boson in the SM as a function of the mass.
• Figure 3: Two important Higgs boson production processes at the ILC. The Higgsstrahlung process (Left), the W-boson fusion process (Middle) and the top-quark association (Right).
• Figure 4: (Left)The production cross sections of the Higgs boson with the mass of 125 GeV at the ILC as a function of the collision energy $\sqrt{s}$. Polarization of the electron beam (80%) and the positron beam (20%) is assumed. (Right) The cross sections of the production processes $e^+e^- \to hZ$, $e^+e^- \to H \nu_e \bar{\nu}_e$, $e^+e^- \to H e^+ e^-$, $e^+e^- \to t \bar{t} H$, $e^+e^- \to HHZ$ and $e^+e^- \to HH \nu_e \bar{\nu}_e$ as a function of the collision energy for the mass of 125 GeV. No polarization is assumed for the initial electron and positron beams.
• Figure 5: Typical diagrams for double Higgs boson production via off-shell Higgsstrahlung (Left) and $W$-boson fusion (Right) processes.