Collider ILC Research Articles

High-precision QED initial state corrections for e+e−→ γ∗/Z∗ annihilation

The precise knowledge of the QED initial state corrections is of instrumental importance in studying high-luminosity measurements in [Formula: see text] annihilation at facilities like LEP, the International Linear Collider ILC, CLIC, a Giga-[Formula: see text] facility, and the planned FCC_ee. Logarithmic corrections of up to [Formula: see text] are necessary with various subleading terms taken into account. This applies to both the inclusive measurement of processes like [Formula: see text] and also the forward–backward asymmetry. As has been shown recently, techniques from massive QCD, such as the computation of massive on-shell operator matrix elements, can be used for these calculations. We give an introduction to this topic and present both the calculation methods and the numerical corrections having been reached so far.

Energy correlation of bottom quarks from decays of top quarks in electron–positron annihilation

Joint energy distribution of the bottom quark and antiquark from decays of the top quark and antiquark produced in the reaction is studied. Main emphasis is put on CP-violation effects in the interaction of the photon and Z boson with the top quarks. Energy asymmetries of b and quarks, which give access to the CP-violating terms, are considered. To estimate the magnitude of these asymmetries, the CP-violating γtt and Ztt couplings are calculated in one-loop model with exchange of the Higgs boson with the mass of 125 GeV. Interaction of this boson with the top quarks is assumed to include scalar and pseudoscalar couplings. Values of these couplings are constrained from the recent CMS analysis. Energy dependence of the asymmetries of b and quarks is calculated up to TeV and some interesting features of their behavior are observed. These observables can be of interest for future studies at electron–positron colliders CLIC and ILC.

B-L extension of the SM - Z′ and heavy Higgs boson analysis at future e+ e− linear colliders ILC and CLIC

We propose a U(1)B−L (baryon minus lepton) extension to the Standard Model, which adds a complex singlet to the scalar sector where an extra neutral gauge boson Z′ corresponding to the U(1)B−L gauge symmetry and an extra SM like singlet scalar H (heavy Higgs) are predicted. We consider the mixture of the Z and Z′. The model also yields Majorana masses for three right handed neutrinos. We study the phenomenology of the light h and heavy H Higgs boson production and decay at future e+ e− linear colliders with center-of-mass energies of √s = 500 − 3000 GeV and integrated luminosities of ℒ = 500 − 2000 fb−1. The study includes the Higgs-strahlung processes e+ e− → (Z Z′) → Zh, e+ e− → (Z Z′) → ZH, and we complement our previous works with the addition of the process.

Optimizing the performance of a high-granularity silicon-pad EM calorimeter

A silicon-based fine granularity calorimeter is a potential technology for the future International Linear Collider ILC, the future circular collider CEPC, and is also the chosen technology for the upgraded CMS experiment of the Large Hadron Collider. Active silicon sensing pads are used as MIP counters and the standard calibration of the calorimeter uses weights based on the average energy loss, dEdx. In this work, the limitations of the dEdx calibration method in terms of energy linearity, scale and resolution are explored. In the case of a calorimeter with varying passive layer thickness as the one planned for CMS, the dEdx method leads to a significant constant term in the resolution function and a non-linearity of energy response. For these reasons, a method based on the calorimeter sampling fraction that exploits the per-event measured shower depth is presented and shown to deliver superior absolute energy scale, linearity and resolution. Calorimetric designs in which the back of the shower is sampled less, offer reduced cost without loss in performance. Therefore, a proper calibration as proposed here is crucial in obtaining the most cost- and performance-effective silicon-sampling calorimeter design.

Optimization of an hybrid positron source using channeling

The hybrid positron source made of a crystal-radiator, as a source of channeling radiation, and an amorphous converter is briefly described. Optimization of the heating effects and thermal shocks led to a granular converter made of small tungsten spheres. Simulation results with application to two linear collider projects CLIC and ILC are presented. A test operated with this kind of source at KEK is described and the results gathered last year, reported. Plans for the future are briefly described.

Prospects of high energy photon colliders

Photon colliders (γγ, γe) have been considered a natural addition to e+e− linear-collider projects for more than 30 years [1, 2]. It was a common opinion that such linear collider with four types of colliding beams (plus e+e−) would be the best instrument for the study of particles physics at energies from 100 GeV to several TeV where a lot of new physics was expected, including the dark matter. Following the discovery of the Higgs boson at LHC (and nothing else), the physics community has been actively considering various approaches to building a Higgs factories for precision measurement of the Higgs properties, among them there are several proposals of photon colliders (PC). In this paper, following a brief discussion of general situation in particles physics and the place of the photon collider among candidates for future colliders, I give an overview of photon colliders based on linear colliders ILC and CLIC and of more recently proposed photon-collider Higgs factories (with no e+e− collision option) based on recirculation linacs in ring tunnels.

Photon collider Higgs factories

The discovery of the Higgs boson (and still nothing else) have triggered appearance of many proposals of Higgs factories for precision measurement of the Higgs properties. Among them there are several projects of photon colliders (PC) without e+e− in addition to PLC based on e+e− linear colliders ILC and CLIC. In this paper, following a brief discussion of Higgs factories physics program I give an overview of photon colliders based on linear colliders ILC and CLIC, and of the recently proposed photon-collider Higgs factories with no e+e− collision option based on recirculation linacs in ring tunnels.

Track reconstruction at the ILC: the ILD tracking software

One of the key requirements for Higgs physics at the International Linear Collider ILC is excellent track reconstruction with very good momentum and impact parameter resolution. ILD is one of the two detector concepts at the ILC. Its central tracking system comprises of an outer Si-tracker, a highly granular TPC, an intermediate silicon tracker and a pixel vertex detector, and it is complemented by silicon tracking disks in the forward direction. Large hit densities from beam induced coherent electron-positron pairs at the ILC pose an additional challenge to the pattern recognition algorithms. We present the recently developed new ILD tracking software, the pattern recognition algorithms that are using clustering techniques, Cellular Automatons and Kalman filter based track extrapolation. The performance of the ILD tracking system is evaluated using a detailed simulation including dead material, gaps and imperfections.

Luminosity measurement at ILC

In this paper we describe a method of luminosity measurement at the future linear collider ILC that estimates and corrects for the impact of the dominant sources of systematic uncertainty originating from the beam-induced effects and the background from physics processes. Based on the relativistic kinematics of the collision frame of the Bhabha process, the beam-beam related uncertainty is reduced to a permille independently of the precision with which the beam parameters are known. With the specific event selection, different from the isolation cuts based on topology of the signal used at LEP, combined with the corrective methods we introduce, the overall systematic uncertainty in the peak region above 80% of the nominal center-of-mass energy meets the physics requirements to be at the few permille level at all ILC energies.

Simulations and Measurements for a concept of powering CALICE-AHCAL at a train-cycled accelerator

Improving calorimetry by usage of the particle-flow algorithm requires to record the details of the shower development. Therefore a high granularity analogue readout hadron calorimeter (AHCAL) with small sensors and with electronics handling the enormous amount of channels, ≈ 40 000/m3, is required. Homogeneity is maintained by avoiding cooling tubes in the active volume and only cooling at the service end.For this concept low power consumption per channel, 40 μW, is essential. Future linear e+e−− collider designs, ILC or CLIC, foresee duty cycles for the bunch delivery. At ILC bunch trains of 1 ms duration are followed by long breaks of 200 ms. Power cycling the front end electronics with the train structure can reduce power consumption by a factor 100. However for a full scale CALICE-AHCAL switched currents reach magnitudes of kilo-amperes.This paper describes the design chain from front end PCB's through to external power supplies. By simulations a concept is developed, in which effects of electromagnetic interferences are kept small and localized. The goal is to keep current loops small, to limit the switched current to the region near the switched consumer and to allow only small frequency currents to spread out further into the system. By that analogue performance can be kept high and parasitic couplings to the surrounding metal structures and other sub-detectors will be minimized. Measurements with existing prototypes support the validity of the simulations.

The International Linear Collider

AbstractA high energy electron positron collider is proposed to complement the large hadron collider, LHC, which has started taking data at CERN, Geneva, Switzerland. Based on superconducting acceleration technology the International Linear Collider ILC is offering a mature proposal. It will deliver high luminosity electron positron collisions at 500 GeV upgradable to 1 TeV. Experimentation at such a collider presents many unique challenges, if the huge physics potential should be harvested efficiently. In this paper after a brief review of the state of the accelerator proposal the state of the preparation of the experimental program is discussed.

ELECTROWEAK PRECISION PHYSICS FROM LEP TO LHC AND ILC

Electroweak precision physics is reviewed from the LEP era with implications for Higgs bosons and supersymmetry, together with expectations for the LHC and a future Linear Collider ILC.

Higgs boson pair production through gauge boson fusion at linear colliders within the general 2HDM

Inclusive Higgs boson pair production through the mechanism of gauge boson fusion e+e−→V∗V∗→hh+X (V=W±,Z) in the general Two-Higgs-Doublet Model (2HDM), with h=h0,H0,A0,H±, is analyzed at O(αew4) in the linear colliders ILC and CLIC. This kind of processes is highly sensitive to the trilinear (3H) Higgs boson self-interactions and hence can be a true keystone in the reconstruction of the Higgs potential. For example, in the ILC at 1 TeV, the most favorable scenarios yield cross-sections up to roughly 1 pb, thus entailing 105 events per 100 fb−1 of integrated luminosity, whilst remaining fully consistent with the perturbativity and unitarity bounds on the 3H couplings, the electroweak precision data and the constraints from B(b→sγ). Comparing with other competing mechanisms, we conclude that the Higgs boson-pair events could be the dominant signature for Higgs-boson production in the TeV-class linear colliders for a wide region of the 2HDM parameter space, with no counterpart in the Minimal Supersymmetric Standard Model (MSSM). Owing to the extremely clean environment of these colliders, inclusive 2H events should allow a comfortable tagging and might therefore open privileged new vistas into the structure of the Higgs potential.

Two Higgs bi-doublet left-right model with spontaneous P and CP violation

A left-right symmetric model with two Higgs bi-doublet is shown to be a consistent model for both spontaneous P and CP violation. The flavor changing neutral currents can be suppressed by the mechanism of approximate global U(1) family symmetry. The constraints from neural K meson mass difference Δm K are calculated and it is demonstrated that a right-handed gauge boson W 2 contribution in box-diagrams with mass well below 1 TeV is allowed due to a cancelation caused by a light-charged Higgs boson with a mass range of 150–300 GeV. The W 2 contribution to ε K can be suppressed from an appropriate choice of additional CP phases appearing in the right-handed Cabbibo-Kobayashi-Maskawa matrix. The model is also found to be fully consistent with B 0 mass difference Δm B and the mixing induced CP violation sin2β J/ Ψ, which is usually difficult for the model with only one Higgs bi-doublet. The new physics beyond the standard model can be directly searched at the colliders LHC and ILC.

Gauge theory model of the neutrino and new physics beyond the standard model

Majorana features of neutrinos and SO(3) gauge symmetry of three families enable us to construct a gauge model of neutrino for understanding naturally the observed smallness of neutrino masses and the nearly tri-bimaximal neutrino mixing when combining together with the mechanism of approximate global U(1) family symmetry. The vacuum structure of SO(3) symmetry breaking is found to play an important role. The mixing angle $\theta_{13}$ and CP-violating phases governed by the vacuum of spontaneous symmetry breaking are in general non-zero and testable experimentally at the allowed sensitivity. The model predicts the existence of vector-like SO(3) triplet charged leptons and vector-like SO(3) triplet Majorana neutrinos as well as SO(3) tri-triplet Higgs bosons, some of them can be light and explored at the colliders LHC and ILC.

SUPERSYMMETRY AT AND BEYOND THE LHC

Prospects for SUSY discoveries and measurements at future colliders LHC and ILC are discussed. The problem of reconstructing the underlying theory and SUSY breaking mechanism is also addressed.

Higgs Particle: The Origin of Mass

The Higgs particle is a new elementary particle predicted in the Standard Model of the elementary particle physics. It plays a special role in the theory of mass generation of quarks, leptons, and gauge bosons. In this article, theoretical issues on the Higgs mechanism are first discussed, and then experimental prospects on the Higgs particle study at the future collider experiments, LHC and ILC, are reviewed. The Higgs coupling determination is an essential step to establish the mass generation mechanism, which could lead to a deeper understanding of particle physics.

Precision Physics at the International Linear Collider

Despite the great success of the Standard Model, many key questions in particle physics and cosmology are unanswered today. Together with the Large Hadron Collider LHC, starting in 2007, the International Linear Collider ILC as the next project planned at the high energy frontier, will play a crucial role in tackling many of these most exciting questions. The high precision achievable with experiments at the ILC will be indispensable in order to reach definite conclusions about many features of new physics expected at the TeV scale. This contribution presents prominent physics examples and describes detector challenges and the project status.

One-loop photonic corrections to Bhabha scattering in d=4-2ε dimensions

The luminosity measurement at the projected International Linear e+e- Collider ILC is planned to be performed with forward Bhabha scattering with an accuracy of the order of 10-4. A theoretical prediction of the differential cross-section has to include one-loop weak corrections, with leading higher order terms, and the complete two-loop QED corrections. Here, we present the weak part and the virtual one-loop photonic corrections. For the photonic corrections, the expansions in ε=(4-d)/2 are derived with inclusion of the terms of order ε in order to match the two-loop accuracy. For the photonic box master integral in d dimensions we compare several different methods of evaluation.