International Linear Collider Research Articles

Japan hopes to staff up to host the International Linear Collider

Japan hopes to staff up to host the International Linear Collider

Physics at ILC

The physics case for the International Linear Collider (ILC) project is discussed. The project is proposed to be built in Japan and a final decision has to be taken in 2016 on a government level. The initial data taking with e +e - beams is planned at the center-of-mass energy of 500 GeV with following runs at 250 GeV and 350 GeV. Potential physics studies at ILC are discussed with a special attention to the measurements, which are expected to have a better sensitivity at ILC in respect to the LHC experiments.

Z–Z' mixing effects in W boson pair production processes at hadron and lepton high-energy colliders

Potential possibilities to detect the effects of Z–Z' mixing in the W-pair production process in proton-proton and electron–positron collisions at the Large Hadron Collider (LHC) and International Linear Collider (ILC) have been studied. It has been established that the processes of W boson pair production are very sensitive to the angle of Z–Z' mixing and their measurements in current and future experiments will make it possible to improve modern restrictions on the angle of Z–Z' mixing in the models with extended gauge sector. At a nominal energy of 14 TeV and an integral luminosity of 100 fb–1, the LHC collider can offer much more precise information on the parameter of Z–Z' mixing and the mass M2 than can be obtained using the ILC leptonic collider (0.5 TeV).

Beam Polarization at the ILC: Physics Case and Realization

The International Linear Collider (ILC) is a proposed [Formula: see text] collider, focused on precision measurement of the Standard Model and new physics beyond. Polarized beams are a key element of the ILC physics program. The physics studies are accompanied by an extensive R&D program for the creation of the polarized beams and the measurement of their polarization. This contribution will review the advantages of using beam polarization and its technical aspects and realization, such as the creation of polarized beams and the measurement of the polarization.

Natural NMSSM with a light Singlet Higgs and Singlino LSP

Supersymmetry (SUSY) is an attractive extension of the Standard Model (SM) of particle physics which solves the SM hierarchy problem. Motivated by the theoretical $\mu$-term problem of the Minimal Supersymmetric Model (MSSM), the Next-to MSSM (NMSSM) can also account for experimental deviations from the SM like the anomalous muon magnetic moment and the dark matter relic density. Natural SUSY, motivated by naturalness considerations, exhibits small fine tuning and a characteristic phenomenology with light higgsinos, stops and gluinos. We describe a scan in NMSSM parameter space motivated by Natural SUSY and guided by the phenomenology of an NMSSM with a slightly broken Peccei-Quinn symmetry and a lightly coupled singlet. We identify a scenario which survives experimental constraints with a light singlet Higgs and a singlino lightest SUSY particle. We then discuss how the scenario is not presently excluded by searches at the Large Hadron Collider (LHC) and which channels are promising for discovery at the LHC and International Linear Collider.

Sneutrino identification in tau pair production at ILC with polarized beams

Many scenarios of new physics can lead to deviations of the observables (cross sections, asymmetries) from the Standard Model predictions in e+e- collision. The possibility of uniquely identifying the indirect effects of s-channel sneutrino exchange, as predicted by supersymmetric theories with R-parity violation, against other new physics scenarios in high-energy electron-positron annihilation into tau pairs at the International Linear Collider has been studied.

Hadronic structure of the photon at smallxin holographic QCD

We present our analysis on the photon structure functions at small Bjorken variable x in the framework of the holographic QCD. In the kinematic region, a photon can fluctuate into vector mesons and behaves like a hadron rather than a pointlike particle. Assuming the Pomeron exchange dominance, the dominant hadronic contribution to the structure functions is computed by convoluting the probe and target photon density distributions obtained from the wave functions of the U(1) vector field in the five-dimensional AdS space and the Brower-Polchinski-Strassler-Tan Pomeron exchange kernel. Our calculations are in agreement with both the experimental data from OPAL collaboration at LEP and those calculated from the parton distribution functions of the photon proposed by Gl\"uck, Reya, and Schienbein. The predictions presented here will be tested at future linear colliders, such as the planned International Linear Collider.

A study of the measurement precision of the Higgs boson decaying into tau pairs at the ILC

We evaluate the measurement precision of the production cross section times the branching ratio of the Higgs boson decaying into tau lepton pairs at the International Linear Collider (ILC). We analyze various final states associated with the main production mechanisms of the Higgs boson, the Higgs-strahlung and WW-fusion processes. The statistical precision of the production cross section times the branching ratio is estimated to be 2.6% and 6.9% for the Higgs-strahlung andWW-fusion processes, respectively, with the nominal integrated luminosities assumed in the ILC Technical Design Report; the precision improves to 1.0% and 3.4% with the running scenario including possible luminosity upgrades. The study provides a reference performance of the ILC for future phenomenological analyses.

LCFIPlus: A framework for jet analysis in linear collider studies

We report on the progress in flavor identification tools developed for a future e+e− linear collider such as the International Linear Collider (ILC) and Compact Linear Collider (CLIC). Building on the work carried out by the LCFIVertex collaboration, we employ new strategies in vertex finding and jet finding, and introduce new discriminating variables for jet flavor identification. We present the performance of the new algorithms in the conditions simulated using a detector concept designed for the ILC. The algorithms have been successfully used in ILC physics simulation studies, such as those presented in the ILC Technical Design Report.

Indirect reach of heavy MSSM Higgs bosons by precision measurements at future lepton colliders

In the Minimal Supersymmetric Standard Model (MSSM), the bottom Yukawa coupling of the Higgs boson can considerably deviate from its Standard Model prediction due to nondecoupling effects. We point out that the ratio of the Higgs boson decay branching fraction to a bottom quark pair and that to a W-boson pair from the same production channel is particularly sensitive to large additional MSSM Higgs boson mass regions at future electron–positron colliders. Based on this precision measurement, we explicitly show the indirect discovery reach of the additional Higgs bosons according to planned programs of the International Linear Collider.

Signal of doubly charged Higgs ate+e−colliders

Masses and signals of the production of Doubly charged Higgses(DCH) in the framework of the supersymmetric reduced minimal 3-3-1 model(SUSYRM331) are investigated. In the DCH sector, weprove that there always exists a region of the parameter space where the mass of the lightest DCH is in order of $\mathcal{O}(100)$ GeV even when all other new particles are very heavy.The lightest DCH mainly decays to two same-sign leptons while the dominated decay channels of the heavy DCHs are those decay to heavy particles. We analyze each production cross section for $e^+e^- \rightarrow H^{++} H^{--}$ as a function of a few kinematic variables, which are useful to discuss the creation of the DCHs in the $e^+e^-$ colliders as a signal of new physics beyond the Standard Model. The numerical study shows that the cross sections for creating the lightest DCH can reach values of few pbs. The two other DCHs are too heavy, beyond the observable range of experiments. The lightest DCH may be detected by the International Linear Collider (ILC) or the Compact LInear Collider (CLIC) by searching its decay to a same-sign charged lepton pair.

Statistical model for field emitter activation on metallic surfaces used in high-gradient accelerating structures

Both super- and normal-conducting high-gradient linear accelerators are limited by enhanced field emission (EFE) in the accelerating structures, e.g. due to power loss or ignition of discharges. We discuss the dependence of the number density of typical emitters, i.e. particulates and surface defects, on the electric field level at which they are activated for naturally oxidized metallic surfaces. This activation is explained by the transition of a metal–insulator interface into geometric features that enhance the EFE process. A statistical model is successfully compared to systematic studies of niobium and copper relevant for recent and future linear accelerators. Our results show that the achievable surface quality of Nb might be sufficient for the suppression of EFE in the superconducting accelerating structures for the actual European XFEL but not for the planned International Linear Collider. Moreover, some effort will be required to reduce EFE and thus the breakdown rate of the normal conducting Cu structures for the Compact Linear Collider.

PromptJ/ψproduction in association with acc¯pair within the framework of nonrelativistic QCD via photon-photon collisions at the International Linear Collider

We present a systematical study on the prompt $J/\psi$ production in association with a $c\bar{c}$ pair via the process, $\gamma\gamma \to H(c\bar{c}) +c+\bar{c}$, within the framework of non-relativistic QCD at the future high-energy $e^{+}e^{-}$ collider - International Linear Collider (ILC), including both direct and feed-down contributions. For direct $J/\psi$ production, the states with color-octet channels, especially the $^3P_J^{[8]}$ and $^1S_0^{[8]}$ ones, provide dominant contribution to the production cross-section, which are about fifty-two times over that of the color-singlet one. This is clearly shown by the transverse momentum ($p_t$) and rapidity distributions. The feed-down contribution from $\psi'$ and $\chi_{cJ}$ ($J=0,1,2$) is sizable, which is about $20\%$ to the total prompt cross-section. Besides the yields, we also calculate the $J/\psi$ polarization parameter $\lambda$. In small $p_t$ region, the polarization of the prompt $J/\psi$ is longitudinal due to large contributions through the $^3P_J^{[8]}$ channel, and becomes transverse in high $p_t$ region due to $^3S_1^{[8]}$ channel. Thus the $J/\psi$ production via photon-photon collisions at the ILC shall provide a useful platform for testing the color-octet mechanism.

Gravitational mass of relativistic matter and antimatter

The universality of free fall, the weak equivalence principle (WEP), is a cornerstone of the general theory of relativity, the most precise theory of gravity confirmed in all experiments up to date. The WEP states the equivalence of the inertial, m, and gravitational, mg, masses and was tested in numerous occasions with normal matter at relatively low energies. However, there is no confirmation for the matter and antimatter at high energies. For the antimatter the situation is even less clear – current direct observations of trapped antihydrogen suggest the limits −65<mg/m<110 not excluding the so-called antigravity phenomenon, i.e. repulsion of the antimatter by Earth. Here we demonstrate an indirect bound 0.96<mg/m<1.04 on the gravitational mass of relativistic electrons and positrons coming from the absence of the vacuum Cherenkov radiation at the Large Electron–Positron Collider (LEP) and stability of photons at the Tevatron collider in presence of the annual variations of the solar gravitational potential. Our result clearly rules out the speculated antigravity. By considering the absolute potential of the Local Supercluster (LS), we also predict the bounds 1−4×10−7<mg/m<1+2×10−7 for an electron and positron. Finally, we comment on a possibility of performing complementary tests at the future International Linear Collider (ILC) and Compact Linear Collider (CLIC).

Design, fabrication and characterization of multi-guard-ring furnished [formula omitted] silicon strip detectors for future HEP experiments

Si detectors, in various configurations (strips and pixels), have been playing a key role in High Energy Physics (HEP) experiments due to their excellent vertexing and high precision tracking information. In future HEP experiments like upgrade of the Compact Muon Solenoid experiment (CMS) at the Large Hadron Collider (LHC), CERN and the proposed International Linear Collider (ILC), the Si tracking detectors will be operated in a very harsh radiation environment, which leads to both surface and bulk damage in Si detectors which in turn changes their electrical properties, i.e. change in the full depletion voltage, increase in the leakage current and decrease in the charge collection efficiency. In order to achieve the long term durability of Si-detectors in future HEP experiments, it is required to operate these detectors at very high reverse biases, beyond the full depletion voltage, thus requiring higher detector breakdown voltage. Delhi University (DU) is involved in the design, fabrication and characterization of multi-guard-ring furnished ac-coupled, single sided, p+n−n+ Si strip detectors for future HEP experiments. The design has been optimized using a two-dimensional numerical device simulation program (TCAD-Silvaco). The Si strip detectors are fabricated with eight-layers mask process using the planar fabrication technology by Bharat Electronic Lab (BEL), India. Further an electrical characterization set-up is established at DU to ensure the quality performance of fabricated Si strip detectors and test structures. In this work measurement results on non irradiated Si Strip detectors and test structures with multi-guard-rings using Current Voltage (IV) and Capacitance Voltage (CV) characterization set-ups are discussed. The effect of various design parameters, for example guard-ring spacing, number of guard-rings and metal overhang on breakdown voltage of test structures have been studied.

Effects of Z−Z′ mixing in double W-bosons production at the large hadron collider

The potential of the Large Hadron Collider (LHC) for searches for effects associated with Z−Z′ mixing in the hadroproduction of W±-boson pairs is studied. The results of our numerical analysis are presented in the form of constraints obtained for the Z−Z′ mixing angle and the Z′-boson mass from the semileptonic channel of W±-boson decay, pp → WW → lνjj + X (l = e or μ), at nominal collider energy and integrated luminosity (\(\sqrt s \) = 14 TeV and Lint = 100 fb−1). The process of double W±-boson production was found to be highly sensitive to the Z−Z′ mixing angle [|ϕ| ~ O(10−3)]. Owing to this, the present-day constraints on this angle can be either improved or reproduced, depending on the choice of model. It was also shown that, upon tripling the LHC luminosity, it will become possible not only to improve the current constraints on the Z−Z′ mixing angle for all Z′ models being considered but also to reach a sensitivity level higher than that of the future lepton collider also known as International Linear Collider or ILC (0.5 TeV).

Indirect probe of electroweak-interacting particles at future lepton colliders

Various types of electroweak-interacting particles, which have non-trivial charges under the $\mathrm{SU}(2)_L \times \mathrm{U}(1)_Y$ gauge symmetry, appear in various extensions of the Standard Model. These particles are good targets of future lepton colliders, such as the International Linear Collider (ILC), the Compact LInear Collider (CLIC) and the Future Circular Collider of electrons and positrons (FCC-ee). An advantage of the experiments is that, even if their beam energies are below the threshold of the production of the new particles, quantum effects of the particles can be detected through high precision measurements. We estimate the capability of future lepton colliders to probe electroweak-interacting particles through the quantum effects, with particular focus on the wino, the Higgsino and the so-called minimal dark matters, and found that a particle whose mass is greater than the beam energy by 100-1000 GeV is detectable by measuring di-fermion production cross sections with $O(0.1)$\% accuracy. In addition, with the use of the same analysis, we also discuss the sensitivity of the future colliders to model independent higher dimensional operators, and found that the cutoff scales corresponding to the operators can be probed up to a few ten TeV.

Direct detection of singlet dark matter in classically scale-invariant standard model

Classical scale invariance is one of the possible solutions to explain the origin of the electroweak scale. The simplest extension is the classically scale-invariant standard model augmented by a multiplet of gauge singlet real scalar. In the previous study it was shown that the properties of the Higgs potential deviate substantially, which can be observed in the International Linear Collider. On the other hand, since the multiplet does not acquire vacuum expectation value, the singlet components are stable and can be dark matter. In this letter we study the detectability of the real singlet scalar bosons in the experiment of the direct detection of dark matter. It is shown that a part of this model has already been excluded and the rest of the parameter space is within the reach of the future experiment.

Probing top-Z dipole moments at the LHC and ILC

We investigate the weak electric and magnetic dipole moments of top quark-Z boson interactions at the Large Hadron Collider (LHC) and the International Linear Collider (ILC). Their vanishingly small magnitude in the Standard Model makes these couplings ideal for probing New Physics interactions and for exploring the role of top quarks in electroweak symmetry breaking. In our analysis, we consider the production of two top quarks in association with a Z boson at the LHC, and top quark pairs mediated by neutral gauge bosons at the ILC. These processes yield direct sensitivity to top quark-Z boson interactions and complement indirect constraints from electroweak precision data. Our computation is accurate to next-to-leading order in QCD, we include the full decay chain of top quarks and the Z boson, and account for theoretical uncertainties in our constraints. We find that LHC experiments will soon be able to probe weak dipole moments for the first time.

Double vector meson production in the International Linear Collider

In this paper we study double vector meson production in $\gamma \gamma$ interactions at high energies and, using the color dipole picture, estimate the main observables which can be probed at the International Linear Collider (ILC). The total $\gamma (Q_1^2) + \gamma (Q_2^2) \rightarrow V_1 + V_2$ cross-sections for $V_i = \rho$, $\phi$, $J/\psi$ and $\Upsilon$ are computed and the energy and virtuality dependencies are studied in detail. Our results demonstrate that the experimental analysis of this process is feasible at the ILC and it can be useful to constrain the QCD dynamics at high energies.