The International Linear Collider Technical Design Report - Volume 2: Physics (1306.6352v1)

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.

• The paper provides a detailed design for using electron–positron collisions to achieve precise measurements of the Higgs boson’s properties and self-coupling.
• The paper demonstrates rigorous top quark threshold scans and two-fermion process analyses that constrain both Standard Model and beyond Standard Model scenarios.
• The paper highlights the ILC’s capacity to differentiate extended Higgs sector models and probe new physics phenomena such as extra dimensions and fermion compositeness.

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

The Technical Design Report (TDR) for the International Linear Collider (ILC) outlines the machine's potential as a fundamental tool in exploring beyond the Standard Model (BSM) physics. The report consolidates extensive research on the scientific imperatives and technical feasibility of an electron-positron collider. At the core of the discussion is the elucidation of the Higgs sector, precision top quark physics, the W and Z boson properties, and the exploration of new physics processes such as fermion compositeness and extra dimensions.

Higgs Boson Investigations at the ILC

The report emphasizes the compelling need for precision measurement of the Higgs boson properties achieved through the cleaner experimental environment of electron-positron collisions. Compared to the intricacies and ambiguities of hadron collider measurements, the ILC leverages electron-positron collisions to facilitate superior measurements of Higgs mass, quantum numbers, and couplings. By operating at various energy stages (250 GeV, 500 GeV, and 1 TeV), the ILC will make probing investigations into the Higgs boson's interaction with W and Z bosons. This capacity is crucial, especially given the perplexing nature of the EWSB mechanism.

The TDR envisages accurately measuring the Higgs boson's self-coupling, accessible through processes such as $e^+e^- \to ZHH$ and $e^+e^- \to \nu \bar{\nu}HH$. Through such processes, the ILC promises to unravel the details of Higgs potential's structure—thus testing the Standard Model and its innumerable extensions like supersymmetry and composite Higgs models.

Broad Survey of Extended Higgs Sectors

Section 6 of the TDR extensively discusses scenarios beyond the minimal Higgs sector. The report evaluates models including Two Higgs Doublet Models (THDMs), singlet extensions, and triplet models—all pivotal frameworks predicting novel Higgs bosons which the LHC may not fully unravel. The realistic parameters and decays of these models are discussed, with the ILC posited as an adept facility for distinguishing between models, thanks to its exquisite capabilities of identifying mixture of states and precise coupling measurement.

Top Quark Studies and New Physics Sensitivity

The ILC's prowess in providing a platform for precise top quark physics is acknowledged. The facility's ability to probe %%%%2%%%% production thresholds promises to render unparalleled measurements of the top quark mass with high precision—vital for constraining SM predictions and beyond. It is anticipated to improve constraints on top Yukawa coupling, which is a key coupling for heavy particle models like the Casas-Ibarra and Little Higgs frameworks. Importantly, the sensitivity of the ILC to potential deviations in top quark couplings due to BSM phenomena, such as Randall-Sundrum models, is considered vital in elucidating composite Higgs scenarios.

Two-Fermion Processes: Windows to New Interactions

The discussion extends to the ILC's capability in probing simple e+e− to two-fermion final states, which can serve as sensitive indicators for new physics, including Z', compositeness, and extra dimensions. The ILC's precision measurements in these areas, characterized by small standard model backgrounds, could probe models with very high scales and provide new indirect limits on undetected scales, potentially surpassing those available from hadron colliders.

Implications and Future Prospects

The ILC's proposed experimental agenda presents a powerful complement to LHC physics, offering confirmations or discoveries where the LHC might be limited. The ILC's comprehensive analyses promise significant insight into the coupling structure of known particles and possible BSM phenomena. Such fine granularity in ILC measurements is crucial for precisely identifying and constraining theoretical models. The detailed elucidation of each foundational particle physics aspect ensures the ILC's foundational role in potentially revolutionary refinements of the Standard Model and its BSM extensions.

The TDR stands as a monumental synthesis, capturing the profound potential of the ILC as a formidable instrument for high energy physics research, poised to dissect the most cornerstone phenomena of the universe’s building blocks with unmatched precision.