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The International Linear Collider (ILC) is on the table now as a new global energy-frontier accelerator laboratory taking data in the 2030s. The ILC addresses key questions for our current understanding of particle physics. It is based on a proven accelerator technology. Its experiments will challenge the Standard Model of particle physics and will provide a new window to look beyond it. This document brings the story of the ILC up to date, emphasizing its strong physics motivation, its readiness for construction, and the opportunity it presents to the US and the global particle physics community., Comment: 356 pages, Large pdf file (40 MB) submitted to Snowmass 2021; v2 references to Snowmass contributions added, additional authors; v3 references added, some updates, additional authors

We are producing high statistics 250 GeV common MC samples for the ILD physics study using the latest generator, simulation, and reconstruction packages. In the production, we utilize ILCDirac distributed computing environment. The estimated resource requirements, the current status and prospects of the production are presented., Comment: 6 pages, Talk presented at the International Workshop on Future Linear Colliders (LCWS2021), 15-18 March 2021. C21-03-15.1

The International Linear Collider (ILC) is now under consideration as the next global project in particle physics. In this report, we review of all aspects of the ILC program: the physics motivation, the accelerator design, the run plan, the proposed detectors, the experimental measurements on the Higgs boson, the top quark, the couplings of the W and Z bosons, and searches for new particles. We review the important role that polarized beams play in the ILC program. The first stage of the ILC is planned to be a Higgs factory at 250 GeV in the centre of mass. Energy upgrades can naturally be implemented based on the concept of a linear collider. We discuss in detail the ILC program of Higgs boson measurements and the expected precision in the determination of Higgs couplings. We compare the ILC capabilities to those of the HL-LHC and to those of other proposed e+e- Higgs factories. We emphasize throughout that the readiness of the accelerator and the estimates of ILC performance are based on detailed simulations backed by extensive RandD and, for the accelerator technology, operational experience., Comment: 104 pages, 88 figures; v2: minor typo corrections; v3: many minor changes, including small corrections to the Tables and Figures in Section 11

A large scale Monte Carlo production has been pursued since spring 2018 for the ILD detector optimization studies based on physics benchmark processes. A production system based on ILCDirac has been developed to produce samples in timely manner. The system and its performance are presented., Comment: Talk presented at the International Workshop on Future Linear Colliders (LCWS2018), Arlington, Texas, 22-26 October 2018. C18-10-22

A large, world-wide community of physicists is working to realise an exceptional physics program of energy-frontier, electron-positron collisions with the International Linear Collider (ILC). This program will begin with a central focus on high-precision and model-independent measurements of the Higgs boson couplings. This method of searching for new physics beyond the Standard Model is orthogonal to and complements the LHC physics program. The ILC at 250 GeV will also search for direct new physics in exotic Higgs decays and in pair-production of weakly interacting particles. Polarised electron and positron beams add unique opportunities to the physics reach. The ILC can be upgraded to higher energy, enabling precision studies of the top quark and measurement of the top Yukawa coupling and the Higgs self-coupling. The key accelerator technology, superconducting radio-frequency cavities, has matured. Optimised collider and detector designs, and associated physics analyses, were presented in the ILC Technical Design Report, signed by 2400 scientists. There is a strong interest in Japan to host this international effort. A detailed review of the many aspects of the project is nearing a conclusion in Japan. Now the Japanese government is preparing for a decision on the next phase of international negotiations, that could lead to a project start within a few years. The potential timeline of the ILC project includes an initial phase of about 4 years to obtain international agreements, complete engineering design and prepare construction, and form the requisite international collaboration, followed by a construction phase of 9 years.

Precise measurements of electroweak processes at the International Linear Collider (ILC) will provide unique opportunities to explore new physics beyond the Standard Model. Fermion pair productions are sensitive to a new contact interaction or a new heavy gauge boson by comparing cross section and angular distribution with expectations of the new physics models. In this proceedings we report a simulation study of fermion pair productions at a center-of-mass energy of 250 GeV, with a focus on lepton pairs, to demonstrate the potential of the first phase of the ILC., Comment: Talk presented at the International Workshop on Future Linear Colliders (LCWS2017), Strasbourg, France, 23-27 October 2017. C17-10-23.2

The Fine Pixel CCD (FPCCD) is one of the candidate sensor technologies for the ILC vertex detector. The vertex detector is located near the interaction point, thus high radiation tolerance is required. Charge transfer efficiency of CCD is degraded by radiation damage which makes traps in pixels. We measured charge transfer inefficiency (CTI) of a neutron irradiated FPCCD prototype. We observed a degradation of CTI compared with non-irradiated CCD. To improve the CTI of irradiated CCD, we performed the fat-zero charge injection to fill the traps. In this paper, we report a status of CTI improvement., Comment: Talk presented at the International Workshop on Future Linear Colliders (LCWS2016), Morioka, Japan, 5-9 December 2016. C16-12-05.4

We describe an algorithm which has been developed to extract fine granularity information from an electromagnetic calorimeter with strip-based readout. Such a calorimeter, based on scintillator strips, is being developed to apply particle flow reconstruction to future experiments in high energy physics. Tests of this algorithm in full detector simulations, using strips of size 45 x 5 mm^2 show that the performance is close to that of a calorimeter with true 5 x 5 mm^2 readout granularity. The performance can be further improved by the use of 10 x 10 mm^2 tile- shaped layers interspersed between strip layers., Comment: 11 pages, 10 figures

One of the major physics goals at the ILC is the precise measurement of the Higgs coupling constants to b-quarks and c-quarks. To achieve this measurement, we need a high-performance vertex detector leading to precise flavor tagging. For this purpose, we are developing the Fine Pixel CCD (FPCCD) vertex detector. In this paper, we will report on the development status of FPCCDTrackFinder, a new track finder improving tracking efficiency, especially in the low $p_t$ region, and an evaluation result of the flavor tagging performance with FPCCDTrackFinder in the FPCCD vertex detector., Comment: Talk presented at the International Workshop on Future Linear Colliders (LCWS13), Tokyo, Japan, 11-15 November 2013

A feasibility to use the hadronic decay mode of $Z$ for the model independant measurement of the total cross section of Higgs-strahlung process $(\sigma_{Zh})$ at a future $e^+e^-$ collider was studied. For the recoil mass measurement from hadronic decay of $Z$, a simple cut based analysis was applied on samples produced by the ILD full detector simulation at $\sqrt{s}=350$ GeV and 500 GeV using the ILC beam parameters. At $350$ GeV, a bump in the recoil mass distribution was reconstructed, and $\Delta\sigma_{Zh}/\sigma_{Zh}$ = 3.4% was obtained assuming 165 fb$^{-1}$ data with $e^-(e^+)$ beam polarization of -80%(+30%) and +80%(-30%), respectively. At $500$ GeV, clear Higgs boson peak in the recoil mass distribution was not seen, however, from the excess of the events, $\Delta\sigma_{Zh}/\sigma_{Zh}=3.9%$ was obtained assuming 500 fb$^{-1}$ data with $e^-(e^+)$ beam polarization of -80%(+30%)., Comment: 8 pages, 10 figures

This paper summarizes the physics potential of the CLIC high-energy e+e- linear collider. It provides input to the Snowmass 2013 process for the energy-frontier working groups on The Higgs Boson (HE1), Precision Study of Electroweak Interactions (HE2), Fully Understanding the Top Quark (HE3), as well as The Path Beyond the Standard Model -- New Particles, Forces, and Dimensions (HE4). It is accompanied by a paper describing the CLIC accelerator study, submitted to the Frontier Capabilities group of the Snowmass process., Comment: Updated the author list, updated Higgs results and small changes in the text of the Higgs section, updated results on composite Higgs bosons, added and updated references. Final submission for the Snowmass proceedings

Fine pixel CCD (FPCCD) is one of the candidate sensor technologies for the vertex detector used for experiments at the International Linear Collider (ILC). A vertex detector system for the International Large Detector (ILD) using FPCCD sensors has been designed. We report on the R&D status of FPCCD sensors, as well as the vertex detector design for ILD., Comment: 5 pages, 3 figures, LCWS11

This report describes the physics potential and experiments at a future multi-TeV e+e- collider based on the Compact Linear Collider (CLIC) technology. The physics scenarios considered include precision measurements of known quantities as well as the discovery potential of physics beyond the Standard Model. The report describes the detector performance required at CLIC, taking into account the interaction point environment and especially beaminduced backgrounds. Two detector concepts, designed around highly granular calorimeters and based on concepts studied for the International Linear Collider (ILC), are described and used to study the physics reach and potential of such a collider. Detector subsystems and the principal engineering challenges are illustrated. The overall performance of these CLIC detector concepts is demonstrated by studies of the performance of individual subdetector systems as well as complete simulation studies of six benchmark physics processes. These full detector simulation and reconstruction studies include beaminduced backgrounds and physics background processes. After optimisation of the detector concepts and adopting the reconstruction algorithms the results show very efficient background rejection and clearly demonstrate the physics potential at CLIC in terms of precision mass and cross section measurements. Finally, an overview of future plans of the CLIC detector and physics study is given and a list of key detector R&D topics needed for detectors at CLIC is presented., Comment: 257 p, published as CERN Yellow Report CERN-2012-003

Precise measurement of the Higgs boson properties are important issues for the International Linear Collider (ILC) project to understand the particles mass generation mechanism which strongly related to the coupling with the Higgs boson. Large Hadron Collider (LHC) experiments exclude the large area of the predicted Higgs mass region and their results indicate that Higgs boson mass will be light. Even if LHC discovers the Higgs like particle by the end of 2012, Higgs will be identified by the high precision measurement of the Higgs boson properties in ILC and also Higgs measurement verifies the correctness of standard model (SM) or gives some hints toward its beyond. In this study, we evaluate the measurement accuracies of Higgs branching fraction to the H->bb, cc and gg at the center-of-mass energy of 250 and 350 GeV., Comment: 9 pages, 3 figures, proceedings of the 2011 International Workshop on Future Linear Colliders (LCWS11)

One of candidates for the International Linear Collider(ILC)'s vertex detector is the Fine Pixel CCD (FPCCD) with a pixel size of 5 \times 5 (\mum^2). Sensor and readout systems are currently being studied and prototypes have been developed. In this paper we will report on the performance of latest developed readout ASIC prototype as well as the outline of the design strategy for the next ASIC prototype., Comment: 5 pages, 4 figures, 2 tables, presented at the Linear Collider Workshop (LCWS '11), Granada, Spain, 26-30 Sept. 2011

Fine pixel CCD (FPCCD) is an option for the sensor used for the ILC vertex detector to reduce the pixel occupancy due to the high background rate near the interaction point. In this paper, we report on the R&D status of FPCCD sensors and the R&D plan for the sensors and the cooling system., Comment: 4 pages, 3 figures, Proceedings of LCWS/ILC20101

We fabricated a readout ASIC with the fully depleted silicon-on-insulator (FD-SOI) technology for the pair-monitor. The pair-monitor is a silicon pixel device that measures the beam profile of the international linear collider. It utilizes the directional distribution of a large number of electron-positron pairs created by collision of bunches, and is required to tolerate radiation dose of about a few Mrad/year. The irradiation might cause the buried oxide layer of SOI to accumulate charges which interfere with intended functions. We thus performed extensive irradiation tests on the prototype ASIC, and the results are described in this paper., Comment: 4 pages, 3 figures, LCWS10

The LCG GRID system is the indispensable infrastructure for large scale computing required for ILC experiments. It had been used extensively for ILD LOI studies and its use will be further increased in coming DBD studies. Experiences during the LOI era and plan towards DBD study in KEK are presented., Comment: 4 pages, 2 figures, proceedings of the Internationa Linear Collider Workshop LCWS2010, Beijing, China

The scintillator-strip electromagnetic calorimeter (ScECAL) is one of the calorimeter technic for the ILC. To achieve the fine granularity from the strip-segmented layers the strips in odd layers are orthogonal with respect to those in the even layers. In order to extract the best performance from such detector concept, a special reconstruction method and simulation tools are being developed in ILD collaboration. This manuscript repots the status of developing of those tools., Comment: 5 pages, 10 figures, Proceedings for the conference "Iinternational Linear Collider Workshop 2010 in Beijing (LCWS2010)"

We are developing the vertex detector with a fine pixel CCD (FPCCD) for the international linear collider (ILC), whose pixel size is $5 \times 5$ $\mu$m$^{2}$. To evaluate the performance of the FPCCD vertex detector and optimize its design, development of the software dedicated for the FPCCD is necessary. We, therefore, started to develop the software for FPCCD. In this article, the status of the study is reported., Comment: 5 pages, 4 figures, Proceedings of LCWS/ILC2010

We have studied the measurement accuracy of the forward-backward asymmetry of the $e^+e^- \rightarrow t\bar{t}$ process in the 6-jet mode at $\sqrt{s} = 500$ GeV with the ILD detector. In the analysis the vertex charges of b-jets were used to distinguish t from $\bar{t}$ in each event. The distribution of the cosine of the reconstructed polar angle of so identified t or $\bar{t}$ showed a clear forward-backward asymmetry. After the correction for charge misidentification the forward-backward asymmetry was determined to be $A^t_{FB} = 0.334 \pm 0.0079$ for 500 fb$^{-1}$ with the beam polarization combination of $P(e^+, e^-) = (+30\%, -80\%)$, demonstrating a very good statistical accuracy ($\sim 2\%$) even in the 6-jet mode., Comment: 12 pages, 10 figures, Proceedings of the ILC physics working group meetings, KEK

Tau-pair process has been analyzed in the ILD detector model as a benchmark process for LoI. Results of background rejection, forward-backward asymmetry and polarization measurements are obtained with full detector simulation. Impact of detector parameters for tau-pair analysis is also discussed in this paper., Comment: 8 pages, 5 figures, Proceedings for LCWS/ILC2008

As a candidate of the vertex detector for experiments at ILC, fully depleted fine pixel CCDs (FPCCDs) are under development. We describe the basic concept of the FPCCD and report on preliminary results of the performance study of the first prototype FPCCD sensors., Comment: 3 pages, 3 figures, LCWS2008 Proceedings

At the International Linear Collider (ILC), measurement of the beam profile at the interaction point (IP) is a key issue to achieve high luminosity. We studied the beam size measurement by combination of Pair Monitor and BeamCal. We obtained measurement accuracies of 2.7%, and 6.6% for the horizontal, and vertical beam sizes, respectively, for 50 bunch crossings., Comment: 4 pages, 3 figures, Proceedings of LCWS08

At the international linear collider, measurement of the beam profile at the interaction point is a key issue to achieve high luminosity. We report a simulation study on a new beam profile monitor, called the pair monitor, which uses the hit distribution of the electron-positron pairs generated at the interaction point. We obtained measurement accuracies of 5.1%, 10.0%, and 4.0% for the horizontal, vertical, and longitudinal beam size, respectively, for 50 bunch crossings., Comment: 13 pages, 8 figures, 2 tables

We develop the vertex detector for the international linear collider (ILC) using the FPCCD (Fine Pixel CCD), whose pixel size is 5 x 5 um2. Together with the FPCCD sensor, a prototype of the readout ASIC was developed in 2008. The readout ASIC was confirmed to work correctly at slow readout speed (1.5 Mpix/sec). In this letter, we describe the status of the performance study for the readout ASIC., Comment: 4 pages, 5 figures, Proceedings of LCWS08

The pair monitor is a beam profile monitor at interaction point (IP) for the international linear collider (ILC). We have designed and developed the pair monitor as a silicon pixel sensor which is located at about 400 cm from IP. As the first step to develop the pair monitor, the readout ASIC was developed. In this paper, test results of the readout ASIC and the future plan are reported., Comment: 4 pages, 5 figures, Proceedings of LCWS08

The Particle Flow Analysis (PFA) is currently under intense studies as the most promising way to achieve precision jet energy measurements required at the future linear $e^+e^-$ collider. In order to optimize detector configurations and to tune up the PFA it is crucial to identify factors that limit the PFA performance and clarify the fundamental limits on the jet energy resolution that remain even with the perfect PFA and an infinitely granular calorimeter. This necessitates a tool to connect each calorimeter hit in particle showers to its parent charged track, if any, and eventually all the way back to its corresponding primary particle, while identifying possible interactions and decays along the way. In order to realize this with a realistic memory space, we have developed a set of C++ classes that facilitates history keeping of particle tracks within the framework of Geant4. This software tool, hereafter called J4HistoryKeeper, comes in handy in particular when one needs to stop this history keeping for memory space economy at multiple geometrical boundaries beyond which a particle shower is expected to start. In this paper this software tool is described and applied to a generic detector model to demonstrate its functionality., Comment: Accepted for publication in Computer Physics Communications

The Detector Concept Report (DCR) consists of two parts, one for the physics and the other for ILC detectors. It has been prepared as the accompany document of the ILC Accelerator Reference Design Report. The detector DCR describes ILC detector designs, R&Ds on detector technologies and expected performances. The overview of the Detector DCR and the plan for the final release are presented., Comment: 13 pages, 8 figures, to appear in the proceedings of the Internationa Linear Collider Workshop LCWS2007, Hamburg, Germany

It is widely recognized that good jet energy resolution is one of the most important requirements to the detectors for the future linear $e^+e^-$ collider experiments. The Particle Flow Analysis (PFA) is currently under intense studies as the most promising way to achieving the best attainable resolution. In order to clarify the fundamental limits on the jet energy resolution with the PFA, we have developed a set of C++ classes that facilitates history keeping of particle tracks within the framework of Geant4. In this paper this software tool is described and applied to a generic detector model so as to identify fundamental limiting factors to the PFA performance., Comment: To be submitted to Computer Physics Communications

The International Technology Recommendation Panel distributed a list of questions to each major laboratory. Question 30, part b and d, were technology independent and related to the physics goals of the Linear Collider. An international panel, with representation from Asia, Europe, and the Americas, was formed by the World Wide Study during LCWS04 to formulate a response. This is given below and constitutes the response of the world-wide Linear Collider community., Comment: Presented at International Conference on Linear Colliders (LCWS04), Paris, France, 19-24 April, 2004

JLC is an e+e- linear collider designed for experiments at Sqrt(s)=500 GeV with a luminosity of up to about 2.5x10^{34}/cm^2/s. In this talk, after describing the parameters of JLC accelerator and detector, the feasibilities of JLC to study Higgs, Top, and SUSY physics are presented based on the ACFA report., Comment: 20 pages, 28 figures. Presented at the 7th Accelerator and Particle Physics Institute (APPI2002), Iwate, Japan, 13-16 Februrary, 2002. Full quality figures can be obtained from http://www-jlc.kek.jp/~miyamoto/papers/index.html#appi2002

We discuss the sensitivity of the $e^+ e^- \rightarrow W^+ W^-$ cross section at a future $e^+ e^-$ collider with $\sqrt{s}=500$GeV to the non-decoupling effects of a techni-$\rho$ like vector resonance. The non-decoupling effects are parametrized by the chiral coefficients of the electroweak chiral perturbation theory. We define renormalization scale independent chiral coefficients by subtracting the Standard Model loop contributions. We also estimate the size of the decoupling effects of the techni-$\rho$ resonance by using a phenomenological Lagrangian including the vector resonance., Comment: 9 pages, LaTeX with psfig.sty, Talk presented by M. Tanabashi at the Workshop on Physics and Experiments with Linear Collider, Morioka-Appi, Japan, September 8-12 1995