The International Linear Collider Technical Design Report - Volume 2: Physics

TL;DR

The ILC Technical Design Report Volume 2 analyzes how a 500 GeV e+e− collider, upgradable to 1 TeV, can perform precision Higgs physics, top-quark studies, and searches for beyond-Standard-Model phenomena. It emphasizes a staged program (250 GeV, 500 GeV, 1 TeV) with polarized beams and two detectors (ILD and SiD) sharing luminosity via a push-pull scheme, to achieve model-independent measurements of Higgs couplings (including g_hZZ, g_hWW, and loop-induced ggh, γγ), top-Yukawa, and Higgs self-couplings, while probing Z′, extra dimensions, and extended Higgs sectors. The report connects EFT and resonance frameworks (EW chiral Lagrangian) to VV scattering, diboson/triviboson processes, and precision Z-pole measurements (Giga-Z) to constrain new physics scales up to multi-TeV. It documents detailed SUSY scenarios compatible with LHC results, outlining how the ILC can precisely determine masses, mixings, and couplings of electroweak states (neutralinos, charginos, sleptons, stops) and thereby test naturalness and DM hypotheses, including stop coannihilation and higgsino-dominated spectra. Finally, it explores cosmological connections, showing how EW baryogenesis and WIMP dark matter can be studied via Higgs-sector dynamics, neutralino compositions, and Higgs-mediated interactions, illuminating the interplay between collider measurements and cosmology. Overall, the ILC stands as a uniquely capable instrument to deliver high-precision, systematics-controlled insights into Higgs physics, SM validation, and a broad array of NP scenarios at the TeV scale, with broad implications for unification and cosmic evolution.

Abstract

The International Linear Collider Technical Design Report (TDR) describes in four volumes the physics case and the design of a 500 GeV centre-of-mass energy linear electron-positron collider based on superconducting radio-frequency technology using Niobium cavities as the accelerating structures. The accelerator can be extended to 1 TeV and also run as a Higgs factory at around 250 GeV and on the Z0 pole. A comprehensive value estimate of the accelerator is give, together with associated uncertainties. It is shown that no significant technical issues remain to be solved. Once a site is selected and the necessary site-dependent engineering is carried out, construction can begin immediately. The TDR also gives baseline documentation for two high-performance detectors that can share the ILC luminosity by being moved into and out of the beam line in a "push-pull" configuration. These detectors, ILD and SiD, are described in detail. They form the basis for a world-class experimental programme that promises to increase significantly our understanding of the fundamental processes that govern the evolution of the Universe.

Figures (153)

• Figure 1: Simulated$e^{+} e^{-} \rightarrow Z h$ events: Top: $e^{+} e^{-} \rightarrow Z h \rightarrow \mu^{-} \mu^{-} \tau^{+} \tau^{-}$; Bottom: $e^{+} e^{-} \rightarrow Z h \rightarrow b \bar{b} b \bar{b}$ [11].
• Figure 2: Spin asymmetries in$e^{+} e^{-} \rightarrow t \bar{t}$ : For the two fully polarized beam initial state ( $e_{R}^{-} e_{L}^{+}$- red, solid, $e_{L}^{-} e_{R}^{+}$- blue, dotted), the figures show: Top: the energy distributions of the $W$ and $\ell$ (or $d, s$ quark). Bottom: the $\cos \theta$ distributions of the $b$ and $\ell$.
• Figure 3: Spin asymmetries in$e^{+} e^{-} \rightarrow t \bar{t}$ : For the two fully polarized beam initial state ( $e_{R}^{-} e_{L}^{+}$- red, solid, $e_{L}^{-} e_{R}^{+}$- blue, dotted), the figures show: Top: the energy distributions of the $W$ and $\ell$ (or $d, s$ quark). Bottom: the $\cos \theta$ distributions of the $b$ and $\ell$.
• Figure 4: Branching fractions of the Standard Model Higgs as a function of the Higgs mass.
• Figure 5: Regions of stability and instability for the Higgs potential of the Standard Model, in the plane of$m_{h}$ vs. $m_{t}$, from [14]. The right-hand figure show the 1,2 , and $3 \sigma$ contours corresponding to the currently preferred values of the Higgs boson and top quark masses.