International Linear Collider Experiments Research Articles

Full electroweak 𝒪(α) corrections to Higgs-boson production processes with beam polarization at the International Linear Collider

Abstract We present the full ${{\cal O}}(\alpha )$ electroweak radiative corrections to the production of nine Higgs bosons with beam polarization at the International Linear Collider (ILC). The computation is performed with the help of GRACE-Loop. We compare the full ${{\cal O}}(\alpha )$ electroweak radiative corrections with the factorized initial-state radiation (ISR) effects to estimate the pure weak corrections. This reveals that the pure weak corrections are not negligible and should be taken into account for precision measurements of the Higgs-boson property at the ILC experiments.

A novel technique for the measurement of the avalanche fluctuations of a GEM stack using a gating foil

We have developed a novel technique for the measurement of the size of avalanche fluctuations of gaseous detectors using a gating device (gating foil) prepared for the time projection chamber in the international linear collider experiment (ILD-TPC). In addition to the gating function, the gating foil is capable of controlling the average fraction of drift electrons detected after gas amplification. The signal charge width and shape (skewness) for electron–ion pairs created by a pulsed UV laser as a function of the transmission rate of the gating foil can be used to determine the relative variance of gas gain for single electrons. We present the measurement principle and the result obtained using a stack of gas electron multipliers (GEMs) operated in a gas mixture of Ar-CF4(3%)-isobutane(2%) at atmospheric pressure. Also discussed is the influence of the avalanche fluctuations on the spatial resolution of the ILD-TPC.

Electron and ion transmission of the gating foil for the TPC in the ILC experiment

We have developed a gating foil for the time projection chamber envisaged as a central tracker for the international linear collider experiment. It has a structure similar to the Gas Electron Multiplier (GEM) with a higher optical aperture ratio and functions as an ion gate without gas amplification. The transmission rate for electrons was measured in a counting mode for a wide range of the voltages applied across the foil using an 55Fe source and a laser in the absence of a magnetic field. The upper limit of the transmission rate for positive ions was estimated to be 3.36 ± 0.05 (stat. only)) × 10−4 from the measured electron transmission at a relatively low reverse bias voltage applied to the foil (ΔV =−15.5 V). The blocking power of the gating foil was confirmed to be high enough to suppress the influence of ion backflow.

Measurement of the electron transmission rate of the gating foil for the TPC of the ILC experiment

We have developed a gating foil for the time projection chamber envisaged as a central tracker for the international linear collider experiment. It has a structure similar to the Gas Electron Multiplier (GEM) with a higher optical aperture ratio and functions as an ion gate without gas amplification. The transmission rate for electrons was measured in a counting mode for a wide range of the voltages applied across the foil using an 55Fe source and a laser in the absence of a magnetic field. The blocking power of the foil against positive ions was estimated from the electron transmissions.

Searching for the doubly charged scalars in the Georgi–Machacek model via γγ collisions at the ILC

The Georgi–Machacek (GM) model predicts the existence of the doubly-charged scalars [Formula: see text], which can be seen the typical particles in this model and their diboson decay channels are one of the most promising ways to discover such new doubly-charged scalars. Based on the constraints of the latest combined ATLAS and CMS Higgs boson diphoton signal strength data at [Formula: see text] confidence level, we focus on the study of the triple scalar production in [Formula: see text] collisions at the future International Linear collider (ILC): [Formula: see text], where the production cross-sections are very sensitive to the triple scalar coupling parameter [Formula: see text]. Considering the typical same-sign diboson decay modes for the doubly-charged scalars, the possible final signals might be detected via this process at the future ILC experiments.

Search for lepton flavor violation at future lepton colliders

Lepton flavor violating (LFV) processes, [Formula: see text] and [Formula: see text] ([Formula: see text] or [Formula: see text]), via four-Fermi contact interactions at future International Linear Collider (ILC) are studied. Taking account of previous experimental results of LFV processes [Formula: see text] and [Formula: see text], we find that the upper limits on the LFV parameters for [Formula: see text] could be improved at the ILC experiment using the polarized electron beam. The improvement of the upper limits could be nearly an order of magnitude as compared to previous ones.

Energy Reconstruction in a High Granularity Semi-Digital Hadronic Calorimeter for ILC Experiments

The Semi-Digital Hadronic CALorimeter (SDHCAL) is one of the two hadronic calorimeter options proposed by the International Large Detector (ILD) project for the future International Linear Collider (ILC) experiments. It is a sampling calorimeter with 48 active layers made of Glass Resistive Plate Chambers (GRPCs) and their embedded electronics. A fine lateral segmentation is obtained thanks to pickup pads of 1 cm2. This ensures the high granularity required for the application of the Particle Flow Algorithm (PFA) in order to improve the jet energy resolution in the ILC experiments. The performance of the SDHCAL technological prototype was tested successfully in several beam tests at CERN. The main point to be discussed here concerns the energy reconstruction in SDHCAL. Based on Monte Carlo simulation of the SDHCAL prototype using the GEANT4 package, we present different energy reconstruction methods to study the energy linearity and resolution of the detector response to single hadrons. In particular, we highlight a new technique based on the Artificial Neural Network giving promising results compared to analytic methods.

Associated production of the doubly-charged scalar pair with the Higgs boson in the Georgi–Machacek model at the ILC

Abstract Besides the SM-like Higgs boson h , the Georgi–Machacek (GM) model predicts the existence of doubly-charged Higgs bosons H 5 ± ± in the 5-plet representation, which can be seen the typical particles in this model. We first used the latest Higgs boson diphoton signal strength data to find the allowed region at 2 σ confidence level on the plane of the scalar mass values m H and the triple scalar coupling parameter g h H H , and then focus on the study of the triple Higgs production process e + e − → h H 5 + + H 5 − − at the future International Linear collider (ILC). Our numerical results show that, the values of the production cross section are very sensitive to the triple Higgs coupling strength g h H H and can reach the level several fb in the reasonable parameter space. Considering the same-sign diboson decay H 5 ± ± → W ± W ± , the expected discovery reach at the future ILC experiments are also studied.

Lepton flavor violating Higgs couplings and single production of the Higgs boson via eγ collision

Taking into account the constraints on the lepton flavor violation (LFV) couplings of the Standard Model (SM) Higgs boson H with leptons from low energy experiments and the recent Compact Muon Solenoid experiment results, we investigate production of the SM Higgs boson associated with a lepton τ via eγ collision at the International Linear Collider (ILC) and Large Hadron Electron Collider experiments. The production cross sections are calculated and the LFV signals and the relevant SM backgrounds are examined. The LFV signals of the SM Higgs boson might be observed via eγ collision in future ILC experiments.

Single Higgs boson production at the ILC in the left-right twin Higgs model

In this work, we analyze three dominant single SM-like Higgs boson production processes in the left-right twin Higgs model (LRTHM): the Higgs-strahlung (HS) process , the vector boson fusion (VBF) process and the associate production with top pair process for three possible energy stages of the International Linear Collider (ILC), and compared our results with the expected experimental accuracies for various accessible Higgs decay channels. The following observations have been obtained. (1) In the reasonable parameter space, the LRTHM can generate moderate contributions to theses processes with polarized beams. (2) Among various Higgs boson decay channels, the signal strength is the most sensitive to the LRTHM due to the high expected precision. For the production process, the absolute value of may deviate from the SM prediction by over 8.7% and thus may be detectable at the proposed ILC with TeV. (3) ILC experiments may give a strong limit on the scale parameter f: for the case of ILC-250 GeV, for example, the lower limit for parameter f of the LRTHM is f > 1150 GeV at the level.

Pair production of charged and doubly charged Higgs bosons at ILC in the Higgs triplet model

The charged and doubly charged Higgs bosons ( and ) are the typical particles predicted by the Higgs triplet model (HTM) and the observation of these particles might be regarded as direct evidence of the HTM. In this paper, we investigate the pair production of the charged and doubly Higgs bosons at the International Linear Collider (ILC): and . We present the production cross sections and the distributions of the various observables, i.e., the distributions of the transverse momenta and the rapidity distributions for out-going particles. Our numerical results show that, as long as the charged and doubly charged Higgs bosons masses are not too heavy, their possible signals might be detected via these processes in future ILC experiments. A simply phenomenological analysis is also given.

Triple Higgs boson production at ILC in the Higgs triplet model

Besides the Standard Model (SM)-like Higgs boson h, the Higgs Triplet Model (HTM) predicts the existence of charged and doubly charged Higgs bosons (H±and H±±). In this paper, we focus on the study of the triple Higgs production at the International Linear Collider (ILC): e-e+→hH+H-and e-e+→hH++H–. We present the production cross-sections and discuss the relevant SM backgrounds. Our numerical results show that, with reasonable parameter values, the values of the cross-sections for two processes can reach the level several fb and tens of fb, respectively. Due to large production cross-section and small SM background, the possible signals of H±and H±±might be detected via these processes in the future ILC experiments.

Pair production of doubly charged Higgs boson at photon linear collider in the Higgs triplet model

The characteristic feature of the Higgs Triplet Model (HTM) is the existence of the doubly charged Higgs bosons H±±. In this paper, we study the pair production of doubly charged Higgs bosons in γγ collisions at the International Linear Collider (ILC). We present the production cross-sections and the distributions of the various observables, i.e. the distributions of the transverse momenta, the rapidity distributions for doubly charged Higgs bosons and the production angle distributions of the charged Higgs boson pair. Our numerical results show that, the values of the unpolarized cross-sections can reach a few hundreds of fb. We also study the possible final state for the decay mode H±±→W±W± and relevant Standard Model (SM) background. Due to high produced rate and small SM background, the possible signals of H±± might be detected via this process in the future ILC experiments.

The single neutral top-higgs production at LHC and ILC in the Topcolor-Assisted Technicolor Model

In this paper, we study the single neutral top-higgs (ht0) production processes at the CERN Large Hadron Collider (LHC) and the International Linear Collider (ILC). At the LHC, the production rates of processes pp → Z(W)ht0 are too small to detect ht0. However, with the reasonable parameter values, the cross sections can reach the level of 102 fb for qq → qqht0 process and 103 fb for top quark associated production process pp → tht0 + X, respectively. At the ILC, we study the single top-higgs production processes e−γ → νeW−ht0 and γγ → W+W−ht0 in e−γ and γγ collisions. It is found that the production cross sections can reach the level of a few fb with reasonable parameter values. Furthermore, such processes with the flavor-changing decay mode \(h_t^0 \to t\bar c\) might provide typical signatures to detected the top-higgs. Therefore, it is hopeful to find the signal of top-higgs at the LHC and ILC experiments via theses processes and test the TC2 model directly.

Two Higgs bidoublet model with spontaneousPandCPviolation and decoupling limit to the two Higgs doublet model

The two Higgs bidoublet left-right symmetric model (2HBDM) as a simple extension of the minimal left-right symmetric model with a single Higgs bidoublet is motivated to realize both spontaneous parity ($P$) violation and charge conjugation and parity ($CP$) violation while consistent with the low-energy phenomenology without significant fine-tuning. By carefully investigating the Higgs potential of the model, we find that sizable $CP$-violating phases are allowed after the spontaneous symmetry breaking. The mass spectra of the extra scalars in the 2HBDM are significantly different from the ones in the minimal left-right symmetric model. In particular, we demonstrate in the decoupling limit when the right-handed gauge-symmetry-breaking scale is much higher than the electroweak scale, the 2HBDM decouples into the general two Higgs doublet model with spontaneous $CP$ violation and has rich induced sources of $CP$ violation. We show that in the decoupling limit, it contains extra light Higgs bosons with masses around electroweak scale, which can be directly searched at the ongoing LHC and future International Linear Collider experiments.

First test of a power-pulsed electronics system on a GRPC detector in a 3-Tesla magnetic field

Power-pulsed readout potentially offers a solution to the problem of high power consumption of the electronics for detectors at the future International Linear Collider (ILC) experiments. A 33 × 50cm2 Glass Resistive Plate Chamber (GRPC) equipped with a power-pulsed electronics board offering 1cm2 lateral segmentation was successfully tested in a 3-Tesla magnet. A significant reduction in power consumption with no deterioration of the detector performance was obtained when the power-pulsing mode was applied. This result shows that highly granular calorimeters for ILC experiments are not only an attractive but also a realistic option.

Single Production of Doubly Charged Higgs Boson via eγ Collision in Higgs Triplet Model

The Higgs triplet model (HTM) predicts the existence of a pair of doubly charged Higgs bosons H±±. Single production of H±± via eγ collision at the next generation e+e− International Linear Collider (ILC) and the Large Hadron electron Collider (LHeC) is considered. The numerical results show that the production cross sections are very sensitive to the neutrino oscillation parameters. Their values for the inverted hierarchy mass spectrum are larger than those for the normal hierarchy mass spectrum at these two kinds of collider experiments. With reasonable values of the relevant free parameters, the possible signals of the doubly charged Higgs bosons predicted by the HTM might be detected in future ILC experiments.

Pair production of right-handed neutrinos in the left-right twin Higgs model at ILC and LHC

In the framework of the left-right twin Higgs model, we study pair production of the right-handed neutrinos at the International Linear Collider (ILC) and the CERN Large Hadron Collider (LHC). Our numerical results show that the production cross section of the process e + e -→ N (tu) is at the level of several tens fb at the ILC. However, the resonance production cross section can be significantly enhanced to the order of pb. The pair production cross section for the right-handed neutrinos is the level of several hundreds of fb at the LHC. In general, pair production of right-handed neutrinos gives rise to 2 l +4 j signal without missing energy. As long as the right-handed neutrinos are not too heavy, we conclude that its pair production might be used to test for the left-right twin Higgs model at the future ILC and LHC experiments.

Performance of the Scintillator-Strip Electromagnetic Calorimeter Prototype for the Linear Collider Experiment

The scintillator-strip electromagnetic calorimeter (ScECAL) is one of fine granular calorimeters proposed to realize Particle Flow Algorithm for the International Linear Collider experiment. The ScECAL is a sandwitch calorimeter with tungsten and scintillator layers, where the scintillator layer consists of plastic scintillator strips which size of 1 cm × 4.5 cm × 0.2 cm with a small photo-sensor (MPPC) attached at the its edge. In alternate scintillator layers, strips are orthogonally aligned to make a virtual 1× 1 cm2 cell with its crossing area. To establish the ScECAL technology, we have built a prototype of the ScECAL which consists of 30 layers of tungsten and scintillator layers with 2160 scintillator strips in total. In 2008 and 2009 the beam test has been performed at Fermilab meson test beam line to evaluate performance of the ScECAL prototype with various types of beams ranging 1 to 32 GeV. As a preliminary result of the beam test in 2008, we have obtained linearity of energy measurement less than 6% from the perfect linear response. Energy resolution is measured to be Although detailed analyses are still ongoing, those results already establishes feasibility of the ScECAL as the fine granular calorimeter. However as the next step to precisely measure even higher energy jets, we will proceed to even more finely segmented calorimeter with 5 mm width scintillator strips.

Pair production of neutral Higgs bosons from the left-right twin Higgs model via γγ collisions

The left-right twin Higgs (LRTH) model predicts the existence of the neutral Higgs bosons (h, φ0), which can be produced in pairs (φ0φ0, hh, φ0h) via γγ collisions at the next generation e+e− International Linear Collider (ILC). Our numerical results show that the production cross section of the neutral Higgs boson pair φ0φ0 can reach 8.8 fb. The subprocess γγ → φ0φ0 might be used to test the LRTH model in future ILC experiments.