Search

The double Higgs-strahlungs process $e^+e^- \rightarrow ZHH$ allows to access the Higgs self-coupling at center-of-mass energies above $450$ GeV. Its cross-section exhibits a very different behavior as a function of the value of the self-coupling than fusion-type processes like gluon-gluon fusion at LHC (and future hadron colliders) and $WW$ / $ZZ$ fusion at higher energy lepton colliders. Therefore it adds unique information to the picture, in particular should the value of the Higgs self-coupling differ from its Standard Model prediction. The last full evaluation of the potential of the ILC to measure this process is more than ten years old, and since then many of the reconstruction tools have received very significant improvements. This contribution presents the ongoing work in the ILD collaboration to update the ZHH projections for the next European Particle Physics Strategy Update., Comment: contribution to proceedings of LCWS2024, 10 pages

Electroweak Precision Measurements are stringent tests of the Standard Model and sensitive probes to New Physics. Accurate studies of the Z-boson couplings to the first-generation quarks could reveal potential discrepancies between the fundamental theory and experimental data. Future lepton colliders offering high statistics of Z bosons would be an excellent tool to perform such a measurement based on comparison of radiative and non-radiative hadronic decays of the Z boson. Due to the difference in quark charge, the relative contribution of the events with final-state radiation (FSR) directly reflects the ratio of up- and down-type quark decays. Such an analysis requires a proper distinction between photons coming from different sources, including initial-state radiation (ISR), FSR, parton showers and hadronisation. In our talk, we will show how to extract the values of the Z couplings to quarks and present preliminary results of the analysis for ILC., Comment: Presented at the XXX Cracow EPIPHANY Conference on Precision Physics at High Energy Colliders

In this study we investigate the feasibility of detecting heavy neutral leptons ($N_d$) through exotic Higgs decays at the proposed International Linear Collider (ILC), specifically in the channel of $e^+ e^- \to qq~ H$ with $H\to \nu N_d \to \nu~lW \to \nu l~qq$. Analyses based on full detector simulations of the ILD are performed at the center-of-mass energy of 250 GeV for two different beam polarization schemes with a total integrated luminosity of 2 $\mathrm{ab}^{-1}$. A range of heavy neutral lepton masses between the $Z$ boson and Higgs boson masses are studied. The $2\sigma$ significance reach for the joint branching ratio of $BR(H\to\nu N_d)\cdot BR(N_d\to lW)$ is about 0.1\%, nearly independent of the heavy neutral lepton masses, while the $5\sigma$ discovery is possible at a branching ratio of $0.3\%$. Interpreting these results in terms of constraints on the mixing parameters $|\varepsilon_{id}|^2$ between SM neutrinos and the heavy neutral lepton, it is expected to have a factor of 10 improvement from current constraints., Comment: This is the version that has been accepted for publication. Reviewer comments and suggestions have been addressed

This report, as part of the 2021 Snowmass Process, summarizes the current status of collider physics at the Energy Frontier, the broad and exciting future prospects identified for the Energy Frontier, the challenges and needs of future experiments, and indicates high priority research areas., Comment: 128 pages, 41 figures, 17 tables, contribution to Snowmass 2021

This report summarizes the work of the Energy Frontier Topical Group on EW Physics: Heavy flavor and top quark physics (EF03) of the 2021 Community Summer Study (Snowmass). It aims to highlight the physics potential of top-quark studies and heavy-flavor production processes (bottom and charm) at the HL-LHC and possible future hadron and lepton colliders and running scenarios.

The precise measurement of physics observables and the test of their consistency within the standard model (SM) are an invaluable approach, complemented by direct searches for new particles, to determine the existence of physics beyond the standard model (BSM). Studies of massive electroweak gauge bosons (W and Z bosons) are a promising target for indirect BSM searches, since the interactions of photons and gluons are strongly constrained by the unbroken gauge symmetries. They can be divided into two categories: (a) Fermion scattering processes mediated by s- or t-channel W/Z bosons, also known as electroweak precision measurements; and (b) multi-boson processes, which include production of two or more vector bosons in fermion-antifermion annihilation, as well as vector boson scattering (VBS) processes. The latter categories can test modifications of gauge-boson self-interactions, and the sensitivity is typically improved with increased collision energy. This report evaluates the achievable precision of a range of future experiments, which depend on the statistics of the collected data sample, the experimental and theoretical systematic uncertainties, and their correlations. In addition it presents a combined interpretation of these results, together with similar studies in the Higgs and top sector, in the Standard Model effective field theory (SMEFT) framework. This framework provides a model-independent prescription to put generic constraints on new physics and to study and combine large sets of experimental observables, assuming that the new physics scales are significantly higher than the EW scale., Comment: 55 pages; Report of the EF04 topical group for Snowmass 2021; v2: few typos corrected and references added

Based on the framework of Standard Model Effective Field Theory, we performed a few global fits, each containing a subset of dimension-6 operators, for the measurements that are expected at future colliders. The fit for the Higgs and electroweak sector improves what has been done for the European Strategy Update in 2020 on both EFT treatments and experimental inputs. A new comprehensive fit is performed focusing on 4-fermion interactions at future colliders. Top-quark sector is studied in a dedicated fit which restricts the operators and measurements to be directly related to top-quark. A small subset of CP-violating operators involving bosonic fields alone are also investigated. Various running scenarios for future e+e- and Muon Colliders that are suggested in the Snowmass 2021 discussion are considered in the global fits. The outcomes from each fit are expressed in terms of either direct constraint on Wilson Coefficients or precision on Higgs and electroweak effective couplings., Comment: Contributed Paper to Snowmass 2021. Minor updates from v4: corrected typo in FCC-ee240 luminosity in Table 27 and CEPC360 luminosity in Table 28

In this white paper for the Snowmass '21 community planning exercise we provide quantitative prospects for bottom quark mass measurements in high-energy collisions at future colliders that can provide a precise test of the scale evolution, or "running" of quark masses predicted by QCD.

For the precision study at the ILC 250, measurement of $A_{LR}$ is important as it can constrain SMEFT parameters. The current best measured $A_{LR}$ value is $A_{LR} = 0.1514 \pm 0.0019\,(stat) \pm 0.0011\,(syst)$ which was measured at the SLC, and a more precise value is required for the global fit for the new physics search in TeV-scale. At the ILC, we can use the $e^+ e^- \to \gamma Z$ process to evaluate the $A_{LR}$. We performed a full simulation study of the $e^+ e^- \to \gamma Z$ process at the center-of-mass energy of 250 GeV and evaluated how much we can improve the precision of this observable. The statistical error on $A_{LR}$ at the ILC 250 turned out to be $1.8 \times 10^{-4}$. Major source of the systematic error was error from the beam polarization. As other sources of the systematic error, the uncorrelated parts of error on the product of luminosity and selection efficiency for each polarization combination contribute. Including those systematic errors, total absolute error on $A_{LR}$ was estimated to be 0.00025, 8.8 times better precision than that from the SLC (0.00219)., Comment: contribution to Snowmass 2021

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

This paper describes a novel algorithm for tagging jets originating from the hadronisation of strange quarks (strange-tagging) with the future International Large Detector (ILD) at the International Linear Collider (ILC). It also presents the first application of such a strange-tagger to a Higgs to strange ($h \rightarrow s\bar{s}$) analysis with the $P(e^-,e^+) = (-80\%,+30\%)$ polarisation scenario, corresponding to 900 fb$^{-1}$ of the initial proposed 2000 fb$^{-1}$ of data which will be collected by ILD during its first 10 years of data taking at $\sqrt{s} = 250$ GeV. Upper limits on the Standard Model Higgs-strange coupling strength modifier, $\kappa_s$, are derived at the 95% confidence level to be 7.14. The paper includes as well a preliminary study of a Ring Imaging Cherenkov (RICH) system capable of discriminating between kaons and pions at high momenta (up to 25 GeV), and thus enhancing strange-tagging performance at future Higgs factory detectors., Comment: V1: 69 pages; V2: 80 pages, updated figures/numbers, additional appendices

To aid contributions to the Snowmass 2021 US Community Study on physics at the International Linear Collider and other proposed $e^+e^-$ colliders, we present a list of study questions that could be the basis of useful Snowmass projects. We accompany this with links to references and resources on $e^+e^-$ physics, and a description of a new software framework that we are preparing for $e^+e^-$ studies at Snowmass., Comment: 49 pages, 1 figure, 1 table; v2: correction of some web links; v3: new Section 3 with a description of the ILC simulation framework put in place for Snowmass

This paper presents a combined analysis of the potential of a future electron-positron collider to constrain the Higgs, top and electro-weak (EW) sectors of the Standard Model Effective Field Theory (SMEFT). The leading contributions of operators involving top quarks arise mostly at one-loop suppressed order and can be captured by the renormalization group mixing with Higgs operators. We perform global fits with an extended basis of 29 parameters, including both Higgs and top operators, to the projections for the Higgs, top and electro-weak precision measurements at the International Linear Collider (ILC). The determination of the Higgs boson couplings in the 250 GeV stage of the ILC is initially severely degraded by the additional top-quark degrees of freedom, but can be nearly completely recovered by the inclusion of precise measurements of top-quark EW couplings at the LHC. The physical Higgs couplings are relatively robust, as the top mass is larger than the energy scale of EW processes. The effect of the top operators on the bounds on the Wilson coefficients is much more pronounced and may limit our ability to identify the source of deviations from the Standard Model. Robust global bounds on all Wilson coefficients are only obtained when the 500 GeV stage of the ILC is included., Comment: 66 pages, 13 figures

We study the $h \gamma Z$ coupling, which is a loop induced coupling in the Standard Model (SM), to probe new physics. In a global fit based on the SM Effective Field Theory, measurement of the SM $h \gamma Z$ coupling can provide a very useful constraint, in particular for the precise determination of $hZZ$ and $hWW$ couplings. At the International Linear Collider (ILC), there are two direct ways to study the $h \gamma Z$ coupling: one is to measure the branching ratio of the $h \to \gamma Z$ decay and the other to measure the cross section for the $e^+e^- \to h \gamma$ process. We have performed a full simulation study of the $e^+e^- \to h \gamma$ process at the 250 GeV ILC, assuming 2 ab$^{-1}$ data collected by the International Large Detector (ILD). The expected 1$\sigma$ bound on the effective $h\gamma Z$ coupling ($\zeta_{AZ}$) combining measurements of the cross section for $e^+e^- \to h \gamma$ followed by $h \to b \bar{b}$ and the $h \to \gamma Z$ branching ratio is $-0.0015<\zeta_{AZ}<0.0015$. The expected significance for the signal cross section in the fully hadronic $h \to WW^*$ channel is 0.09 $\sigma$ for beam polarizations of $P(e^-,e^+)=(-80\%,+30\%)$., Comment: 11 pages, 8 figures, Talk presented at the International Workshop on Future Linear Colliders (LCWS2019), Sendai, Japan, 28 October-1 November, 2019. C19-10-28. arXiv admin note: text overlap with arXiv:1902.06029

We present an overview of the capabilities that the International Linear Collider (ILC) offers for precision measurements that probe the Standard Model. First, we discuss the improvements that the ILC will make in precision electroweak observables, both from W boson production and radiative return to the Z at 250 GeV in the center of mass and from a dedicated GigaZ stage of running at the Z pole. We then present new results on precision measurements of fermion pair production, including the production of b and t quarks. We update the ILC projections for the determination of Higgs boson couplings through a Standard Model Effective Field Theory fit taking into account the new information on precision electroweak constraints. Finally, we review the capabilities of the ILC to measure the Higgs boson self-coupling., Comment: 58 pages, 8 figures, 13 tables; v2: minor corrections to Table 11; v3: typo corrections; v4: additions to the W boson section

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

We study the $e^+e^-\to h \gamma$ process at the International Linear Collider (ILC) to probe new physics in the $h\gamma Z$ coupling. The study is performed at a center of mass energy of 250 GeV and is based on the full simulation of the International Large Detector (ILD). The expected signal significance is found to be 0.53 $\sigma$ for an integrated luminosity of 2000 fb$^{-1}$ in the case of the standard model. The corresponding 95 $\%$ confidence level upper limit for the signal cross section is 1.08 fb for left-handed beam polarization., Comment: 10 pages, 9 figures, 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.

The International Linear Collider is now proposed with a staged machine design, with the first stage at $\sqrt{s}=$~250 GeV and an integrated luminosity goal of 2~ab$^{-1}$. One of the questions for the machine design is the importance of positron polarization. In this report, we review the impact of positron polarization on the physics goals of the $250$ GeV stage of the ILC and demonstrate that positron polarization has distinct advantages., Comment: 19

This presentation gives the prospects of measuring the general Lorentz structures of $VVH$ ($V=Z$, $\gamma$ and $W$) couplings at the International Linear Collider (ILC). Sensitivities to Higgs CP-even and CP-odd structures are evaluated by using various Higgs production channels and employing measurements of kinematical distributions. The evaluation is performed based on full detector simulation of the International Large Detector (ILD) at center-of-mass energies $\sqrt{s}=$ 250 and 500 GeV. Combined sensitivities on the anomalous $ZZH$ couplings are provided for a realistic operating scenario of the ILC., Comment: 6 pages, 3 figures, EPS-HEP 2017, European Physical Society conference on High Energy Physics

This document is the final report by the Committee on the Scientific Case of the ILC Operating at 250 GeV as a Higgs Factory. This committee was commissioned by the Japan Association of High Energy Physicists. The purpose of this committee is to investigate and compare the capability to determine the energy scale of new phenomena and new principles and the capability to uncover the origin of matter-antimatter asymmetry., Comment: 14 pages; detail plots in http://www.jahep.org/files/ILCmemo170722final.pdf English version will be prepared

The International Linear Collider is now proposed with a staged machine design, with the first stage at 250 GeV with a luminosity goal of 2 ab-1. In this paper, we review the physics expectations for this machine. These include precision measurements of Higgs boson couplings, searches for exotic Higgs decays, other searches for particles that decay with zero or small visible energy, and measurements of e+e- annihilation to W+W- and 2-fermion states with improved sensitivity. A summary table gives projections for the achievable levels of precision based on the latest full simulation studies., Comment: 48 pages, 6 tables, 12 figures; v3: Figures 1, 2, 5 replaced by corrected versions; v4: typo in eq. (16) corrected

The observation of Higgs pair production at high-energy colliders can give evidence for the presence of a triple Higgs coupling. However, the actual determination of the value of this coupling is more difficult. In the context of general models for new physics, double Higgs production processes can receive contributions from many possible beyond-Standard-Model effects. This dependence must be understood if one is to make a definite statement about the deviation of the Higgs field potential from the Standard Model. In this paper, we study the extraction of the triple Higgs coupling from the process $e^+e^-\to Zhh$. We show that, by combining the measurement of this process with other measurements available at a 500 GeV $e^+e^-$ collider, it is possible to quote model-independent limits on the Effective Field Theory parameter c6 that parametrizes modifications of the Higgs potential. We present precise error estimates based on the anticipated ILC physics program, studied with full simulation. Our analysis also gives new insight into the model-independent extraction of the Higgs boson coupling constants and total width from $e^+e^-$ data., Comment: 44 pages, 7 figures; v3 clarifications and new references added; v4 minor corrections in Appendix A, eqs. (86) and (88)

Future e+e- colliders give the promise of model-independent determinations of the couplings of the Higgs boson. In this paper, we present an improved formalism for extracting Higgs boson couplings from e+e- data, based on the Effective Field Theory description of corrections to the Standard Model. We apply this formalism to give projections of Higgs coupling accuracies for stages of the International Linear Collider and for other proposed e+e- colliders., Comment: 34 pages, 4 figures; v4: clarifications and new references added; v5, additional references added

This paper addresses the question of whether the International Linear Collider has the capability of discovering new particles that have not already been discovered at the CERN Large Hadron Collider. We summarize the various paths to discovery offered by the ILC, and discuss them in the context of three different scenarios: 1. LHC does not discover any new particles, 2. LHC discovers some new low mass states and 3. LHC discovers new heavy particles. We will show that in each case, ILC plays a critical role in discovery of new phenomena and in pushing forward the frontiers of high-energy physics as well as our understanding of the universe in a manner which is highly complementary to that of LHC. For the busy reader, a two-page executive summary is provided at the beginning of the document., Comment: 52 pages, 18 figures

In this paper we study the direct production of the diphoton resonance $X$ which has been suggested by 2015 data at the LHC, in $e^+e^-\to X\gamma/XZ$ processes at the ILC. We derive an analytic expression for the scattering amplitudes of these processes, and present a comprehensive analysis for determining the properties of $X$ at the ILC. A realistic simulation study for $e^+e^-\to X\gamma$ is performed based on the full detector simulation to demonstrate the capabilities of the ILC experiment. Complementary to the searches at the LHC, prospects of the measurement of the absolute values of production cross-section are obtained for the ILC using recoil technique without assuming decay modes of $X$. In addition, we have studied the searches for $X\to\rm{invisible}$ and $X\to b\bar{b}$ modes, which are challenging at the LHC, and found that these decay modes can be discovered with high significance if their branching ratios are large enough., Comment: 26 pages, 14 figures; version accepted by PRD

If the gamma-gamma resonance at 750 GeV suggested by 2015 LHC data turns out to be a real effect, what are the implications for the physics case and upgrade path of the International Linear Collider? Whether or not the resonance is confirmed, this question provides an interesting case study testing the robustness of the ILC physics case. In this note, we address this question with two points: (1) Almost all models proposed for the new 750 GeV particle require additional new particles with electroweak couplings. The key elements of the 500 GeV ILC physics program---precision measurements of the Higgs boson, the top quark, and 4-fermion interactions---will powerfully discriminate among these models. This information will be important in conjunction with new LHC data, or alone, if the new particles accompanying the 750 GeV resonance are beyond the mass reach of the LHC. (2) Over a longer term, the energy upgrade of the ILC to 1 TeV already discussed in the ILC TDR will enable experiments in gamma-gamma and e+e- collisions to directly produce and study the 750 GeV particle from these unique initial states., Comment: 39 pages, 5 figures, 5 tables; v2: some references added

We have developed a novel technique for the measurement of the avalanche fluctuation of gaseous detectors using a UV laser. The technique is simple and requires a short data-taking time of about ten minutes. Furthermore, it is applicable for relatively low gas gains. Our experimental setup as well as the measurement principle, and the results obtained with a stack of Gas Electron Multipliers (GEMs) operated in several gas mixtures are presented., Comment: A supplemental material (Addendum to be published in Nucl. Instrum. Methods Phys. Res. A) was added at the end of the manuscript. 8 pages, including 7 figures

This paper presents a full simulation study of the measurement of the production cross section ($\sigma_{\mathrm{ZH}}$) of the Higgsstrahlung process $\mathrm{e^{+}e^{-}\rightarrow ZH}$ and the Higgs boson mass ($M_{\mathrm{H}}$) at the International Linear Collider (ILC), using events in which a Higgs boson recoils against a Z boson decaying into a pair of muons or electrons. The analysis is carried out for three center-of-mass energies $\sqrt{s}$ = 250, 350, and 500 GeV, and two beam polarizations $\mathrm{e_{L}^{-}e_{R}^{+}}$ and $\mathrm{e_{R}^{-}e_{L}^{+}}$, for which the polarizations of $\mathrm{e^{-}}$ and $\mathrm{e^{+}}$ are $\left(P\mathrm{e^{-}},P\mathrm{e^{+}}\right)$ =($-$80\%, +30\%) and (+80\%, $-$30\%), respectively. Assuming an integrated luminosity of 250 $\mathrm{fb^{-1}}$ for each beam polarization at $\sqrt{s}$ = 250 GeV, where the best lepton momentum resolution is obtainable, $\sigma_{\mathrm{ZH}}$ and $M_{\mathrm{H}}$ can be determined with a precision of 2.5\% and 37 MeV for $\mathrm{e_{L}^{-}e_{R}^{+}}$ and 2.9\% and 41 MeV for $\mathrm{e_{R}^{-}e_{L}^{+}}$, respectively. Regarding a 20 year ILC physics program, the expected precisions for the $\mathrm{HZZ}$ coupling and $M_{\mathrm{H}}$ are estimated to be 0.4\% and 14 MeV, respectively. The event selection is designed to optimize the precisions of $\sigma_{\mathrm{ZH}}$ and $M_{\mathrm{H}}$ while minimizing the bias on the measured $\sigma_{\mathrm{ZH}}$ due to discrepancy in signal efficiencies among Higgs decay modes. For the first time, model independence has been demonstrated to a sub-percent level for the $\sigma_{\mathrm{ZH}}$ measurement at each of the three center-of-mass energies. The results presented show the impact of center-of-mass energy and beam polarization on the evaluated precisons and serve as a benchmark for the planning of the ILC run scenario., Comment: arXiv admin note: substantial text overlap with arXiv:1601.06481; v3: Fix typo in Table I

For the International Large Detector concept at the planned International Linear Collider, the use of time projection chambers (TPC) with micro-pattern gas detector readout as the main tracking detector is investigated. In this paper, results from a prototype TPC, placed in a 1 T solenoidal field and read out with three independent GEM-based readout modules, are reported. The TPC was exposed to a 6 GeV electron beam at the DESY II synchrotron. The efficiency for reconstructing hits, the measurement of the drift velocity, the space point resolution and the control of field inhomogeneities are presented., Comment: 22 pages, 19 figures

This article is based on the talk presented at the International Workshop on Future Linear Colliders (LCWS13) which held during November 11-15, 2013 at Tokyo, Japan. We present several analyses related to the Higgs total width study at ILC based on the full detector simulation of ILD, which are \eevvH followed by \Htobb and \HtoWW. The studies show that at $\unit{250}{GeV}$ we can determine the Higgs total width with a relative precision of 11% and the $HWW$ coupling with 4.8%, whereas at $\unit{500}{GeV}$ the expected precision can be significantly improved to 5% and 1.2% respectively, assuming the baseline integrated luminosities of ILC, which are $\unit{250}{fb^{-1}}$ @ $\unit{250}{GeV}$, $\unit{500}{fb^{-1}}$ @ $\unit{500}{GeV}$, and a beam polarization of $P(e^{-},e^{+})=(-80%,+30%)$. A new approach of removing pile-up particles based on multivariate method developed during those analyses is also presented., Comment: Talk presented at the International Workshop on Future Linear Colliders (LCWS13), Tokyo, Japan, 11-15 November 2013; based on previous note LC-REP-2013-022

In the Standard Model (SM) the couplings of the Higgs boson to SM particles and itself (self-couplings) are uniquely specified once the masses of the particles in question as well as the Higgs boson mass are given. Precision measurements of these couplings in the future collider experiments are the key to either verifying the mechanism of the electroweak symmetry breaking in the SM or uncovering physics beyond the SM. This article gives an overview of how various Higgs couplings will be measured at the ILC. Emphasis is put on the ILC's capability of performing fully model independent determination of absolute $HZZ$ and $HWW$ couplings, the Higgs total width, and hence various other Higgs couplings, which cover essentially all the crucial ones including the top-Yukawa coupling $Htt$ and the trilinear Higgs self-coupling $\lambda_{HHH}$. The strategy to get the best precision measurements at the ILC is through staged running, which provides many independent $\sigma\times\mathrm{Br}$ measurements for different production channels and at different energies. A method of global fitting is discussed to utilize all of the available information and to derive combined precisions., Comment: To appear in the proceedings of The European Physical Society Conference on High Energy Physics (EPS-HEP 2013), Stockholm, Sweden, 18-24 July, 2013

In this Analysis we investigated the possibility of the measurement of Higgs self-coupling at ILC through the process $e^++e^-\rightarrow ZHH$ using fast simulation data. So far two combinations of decay modes: $Z\rightarrow q \bar q,H\rightarrow b\bar b, H\rightarrow WW^*$ and $Z\rightarrow l \bar l, H\rightarrow b\bar b, H\rightarrow b\bar b$ were studied. Our preliminary results show that it is very challenging to suppress the huge standard model backgrounds effectively.