International Linear Collider Research Articles

A CMOS pixel sensor prototype for the outer layers of linear collider vertex detector

The International Linear Collider (ILC) expresses a stringent requirement for high precision vertex detectors (VXD). CMOS pixel sensors (CPS) have been considered as an option for the VXD of the International Large Detector (ILD), one of the detector concepts proposed for the ILC. MIMOSA-31 developed at IPHC-Strasbourg is the first CPS integrated with 4-bit column-level ADC for the outer layers of the VXD, adapted to an original concept minimizing the power consumption. It is composed of a matrix of 64 rows and 48 columns. The pixel concept combines in-pixel amplification with a correlated double sampling (CDS) operation in order to reduce the temporal noise and fixed pattern noise (FPN). At the bottom of the pixel array, each column is terminated with a self-triggered analog-to-digital converter (ADC). The ADC design was optimized for power saving at a sampling frequency of 6.25 MS/s. The prototype chip is fabricated in a 0.35 μm CMOS technology. This paper presents the details of the prototype chip and its test results.

Front-end electronics and readout system for the ILD TPC

A high resolution TPC is the main option for a central tracking detector at the future International Linear Collider (ILC). It is planned that the MPGD (Micro Pattern Gas Detector) technology will be used for the readout. A Large Prototype TPC at DESY has been used to test the performance of MPGDs in an electron beam of energies up to 6 GeV. The first step in the technology development was to demonstrate that the MPGDs are able to achieve the necessary performance set by the goals of ILC. For this `proof of principle' phase, the ALTRO front-end electronics from the ALICE TPC was used, modified to adapt to MPGD readout. The proof of principle has been verified and at present further improvement of the MPGD technology is going on, using the same readout electronics. The next step is the 'feasibility phase', which aims at producing front-end electronics comparable in size (few mm2) to the readout pads of the TPC. This development work is based on the succeeding SALTRO16 chip, which combines the analogue and digital signal processing in the same chip. This paper summarizes the status of this work and discusses how the experiences made so far can be exploited to improve the final readout electronics.

The Physics Case of the International Linear Collider

This article summarises the physics case of the International Linear Collider, ILC. It will cover all centre-of-mass energies needed to study the currently known Standard Model particles and the relevant interactions between them with high precision. Its discovery potential with respect to supersymmetric particles and dark matter complements that of the LHC. For the first time, it will be possible to study top-quark pair production through electroweak processes. This offers exciting possibilities to measure the mass of the top quark with highest precision and the electroweak couplings of the top quark in an unambiguous way.

Full [formula omitted] electroweak radiative corrections to [formula omitted] at the ILC with GRACE-Loop

By using the GRACE-Loop system, we calculate the full O(α) electroweak radiative corrections to the process e+e−→e+e−γ, which is important for future investigations at the International Linear Collider (ILC). With the GRACE-Loop system, the calculations are checked numerically by three consistency tests: ultraviolet finiteness, infrared finiteness, and gauge-parameter independence. The results show good numerical stability when quadruple precision is used. In the phenomenological results, we find that the electroweak corrections to the total cross section range from ∼−4% to ∼−21% when s varies from 250 GeV to 1 TeV. The corrections also significantly affect the differential cross sections, which are a function of energies and angles of the final state particles. Such corrections will play an important role in the high-precision program at the ILC.

Photoproduction of doubly heavy baryon at the ILC

In the present paper, we make a detailed study on the doubly heavy baryon photoproduction in the future $e^+e^-$ International Linear Collider (ILC). The baryons $\Xi_{cc}$, $\Xi_{bc}$, and $\Xi_{bb}$ are produced via the channel $\gamma \gamma \to \Xi_{QQ'} +\bar{Q'} +\bar{Q}$, where $Q$ and $Q'$ stand for heavy $c$ or $b$ quark, respectively. As for the $\Xi_{QQ'}$-baryon production, it shall first generate a $(QQ')[n]$-diquark and then form the final baryon via fragmentation, where $[n]$ stands for the color- and spin- configurations for the $(QQ')$-diquark states. According to the non-relativistic QCD theory, four diquark configurations shall provide sizable contributions to the baryon production, e.g., $[n]$ equals $[^3S_1]_{\bar{\textbf{3}}}$, $[^1S_0]_{\textbf{6}}$, $[^3S_1]_{\textbf{6}}$, or $[^1S_0]_{\bar{\textbf{3}}}$, respectively. We adopt the improved helicity amplitude approach for the hard scattering amplitude to improve the calculation efficiency. Total and differential cross sections of those channels, as well as the theoretical uncertainties, are presented. We show that sizable amounts of baryon events can be generated at the ILC, i.e., about $2.0\times 10^{6}$ $\Xi_{cc}$, $2.2\times 10^{5}$ $\Xi_{bc}$, as well as $3.0\times 10^{3}\;\Xi_{bb}$ events are to be generated in one operation year for $\sqrt{S}=500$ GeV and ${\cal L}\simeq 10^{36}$cm$^{-2}$s$^{-1}$.

Searching for dark matter via mono- $$Z$$ Z boson production at the ILC

High energy colliders provide a new unique way to determine the microscopic properties of the dark matter (DM). Weakly interacting massive particles (WIMPs) are widely considered as one of the best DM candidates. It is usually assumed that the WIMP couples to the SM sector through its interactions with quarks and leptons. In this paper, we investigate the DM pair production associated with a $Z$ boson in an effective field theory framework at the International Linear Collider (ILC), which can be used to study the interactions between the DM and leptons. For illustrative purposes, we present the integrated and differential cross sections for the $e^+ e^- \rightarrow \chi \bar{\chi} Z$ process, where the $Z$ boson is radiated from the initial state electron or positron. Meanwhile, we analyze the neutrino pair production in association with a $Z$ boson as the SM background.

Higgs boson coupling measurements and direct searches as complementary probes of the phenomenological MSSM

The parameter space of the minimal supersymmetric standard model (MSSM) can be probed via many avenues, such as by precision measurements of the couplings of the $\ensuremath{\sim}126\text{ }\mathrm{GeV}$ Higgs boson, as well as the direct searches for supersymmetry (SUSY) partners. We examine the connection between these two collider observables at the LHC and International Linear Collider (ILC) in the $19/20$-parameter phenomenological MSSM (pMSSM). Within this scenario, we address two questions: (i) How will potentially null direct searches for SUSY at the LHC influence the predicted properties of the lightest SUSY Higgs boson? (ii) What can be learned about the properties of the superpartners from precision measurements of the Higgs boson couplings? In this paper, we examine these questions by employing three different large sets of pMSSM models with either the neutralino or gravitino being the lightest supersymmetric particle. We make use of the ATLAS direct SUSY searches at the $7/8\text{ }\text{ }\mathrm{TeV}$ LHC as well as expected results from 14 TeV operations, and the anticipated precision measurements of the Higgs boson couplings at the 14 TeV LHC and at the ILC. We demonstrate that the future Higgs coupling determinations can deeply probe the pMSSM parameter space and, in particular, can observe the effects of models that are projected to evade the direct searches at the 14 TeV LHC with $3\text{ }\text{ }{\mathrm{ab}}^{\ensuremath{-}1}$ of integrated luminosity. In addition, we compare the reach of the Higgs coupling determinations to the direct heavy Higgs searches in the ${M}_{A}\ensuremath{-}\mathrm{tan}\ensuremath{\beta}$ plane and show that they cover orthogonal regions. This analysis demonstrates the complementarity of the direct and indirect approaches in searching for supersymmetry, and the importance of precision studies of the properties of the Higgs boson.

Expectations for probing the Higgs–fermion and the Higgs–vector boson couplings at the ILC

Deviations from the standard Higgs sector generated by some new physics at an energy scale Λ could be described by an effective SU(3)c×SU(2)L×U(1) invariant non-renormalizable Lagrangian terms of dimension six. A systematic study of various Higgs boson production × decay channels (γγ, ZZ, WW, bb¯, ττ¯) at the International Linear Collider (ILC) in the SM extension by effective operators is carried out. Statistical methods are used to establish a degree of consistency for the standard Higgs sector with the forthcoming data, using the expected ILC accuracies of the Higgs boson production channels. Global fits in the two-parametric anomalous coupling space indicating possible deviations from the standard Higgs-fermion and Higgs-gauge boson couplings are performed.

Probing the Standard Model with Higgs signal rates from the Tevatron, the LHC and a future ILC

We explore the room for possible deviations from the Standard Model (SM) Higgs boson coupling structure in a systematic study of Higgs coupling scale factor benchmark scenarios using the latest signal rate measurements from the Tevatron and LHC experiments. We employ chi-squared fits performed with HiggsSignals, which takes into account detailed information on signal efficiencies and major correlations of theoretical and experimental uncertainties. All considered scenarios allow for additional non-standard Higgs boson decay modes, and various assumptions for constraining the total decay width are discussed. No significant deviations from the SM Higgs boson coupling structure are found in any of the investigated benchmark scenarios. We derive upper limits on an additional (undetectable) Higgs decay mode under the assumption that the Higgs couplings to weak gauge bosons do not exceed the SM prediction. We furthermore discuss the capabilities of future facilities for probing deviations from the SM Higgs couplings, comparing the high luminosity upgrade of the LHC with a future International Linear Collider (ILC), where for the latter various energy and luminosity scenarios are considered. At the ILC model-independent measurements of the coupling structure can be performed, and we provide estimates of the precision that can be achieved.

Fingerprinting nonminimal Higgs sectors

After the discovery of the standard model-like Higgs boson at the LHC, the structure of the Higgs sector remains unknown. We discuss how it can be determined by the combination of direct and indirect searches for additional Higgs bosons at future collider experiments. First of all, we evaluate expected excluded regions for the mass of additional neutral Higgs bosons from direct searches at the LHC with the 14 TeV collision energy in the two Higgs doublet models with a softly broken ${Z}_{2}$ symmetry. Second, precision measurements of the Higgs boson couplings at future experiments can be used for the indirect search of extended Higgs sectors if the measured coupling constant with the gauge boson slightly deviates from the standard model value. In particular, in the two Higgs doublet model with the softly broken discrete symmetry, there are four types of Yukawa interactions, so that they can be discriminated by measuring the pattern of deviations in Yukawa coupling constants. Furthermore, we can fingerprint various extended Higgs sectors with future precision data by detecting the pattern of deviations in the coupling constants of the standard model-like Higgs boson. We demonstrate how the pattern of deviations can be different among various Higgs sectors that predict the electroweak rho parameter to be unity, such as models with additional an isospin singlet, a doublet, triplets, or a septet. We conclude that, as long as the gauge coupling constant of the Higgs boson slightly differs from the standard model prediction but is enough to be detected at the LHC and its high-luminosity run or at the International Linear Collider, we can identify the nonminimal Higgs sector even without direct discovery of additional Higgs bosons at the LHC.

Characterization of the International Linear Colliderdamping ring optics

A method is presented for characterizing the emittance dilution and dynamic aperture for an arbitrary closed lattice that includes guide field magnet errors, multipole errors and misalignments. This method, developed and tested at the Cornell Electron Storage Ring Test Accelerator (CesrTA), has been applied to the damping ring lattice for the International Linear Collider (ILC). The effectiveness of beam based emittance tuning is limited by beam position monitor (BPM) measurement errors, number of corrector magnets and their placement, and correction algorithm. The specifications for damping ring magnet alignment, multipole errors, number of BPMs, and precision in BPM measurements are shown to be consistent with the required emittances and dynamic aperture. The methodology is then used to determine the minimum number of position monitors that is required to achieve the emittance targets, and how that minimum depends on the location of the BPMs. Similarly, the maximum tolerable multipole errors are evaluated. Finally, the robustness of each BPM configuration with respect to random failures is explored.

A high speed, low power consumption LVDS interface for CMOS pixel sensors

The use of CMOS Pixel Sensors (CPSs) offers a promising approach to the design of vertex detectors in High Energy Physics (HEP) experiments. As the CPS equipping the upgraded Solenoidal Tracker at RHIC (STAR) pixel detector, ULTIMATE perfectly illustrates the potential of CPSs for HEP applications. However, further development of CPSs with respect to readout speed is required to fulfill the readout time requirement of the next generation HEP detectors, such as the upgrade of A Large Ion Collider Experiment (ALICE) Inner Tracking System (ITS), the International Linear Collider (ILC), and the Compressed Baryonic Matter (CBM) vertex detectors. One actual limitation of CPSs is related to the speed of the Low-Voltage Differential Signaling (LVDS) circuitry implementing the interface between the sensor and the Data Acquisition (DAQ) system. To improve the transmission rate while keeping the power consumption at a low level, a source termination technique and a special current comparator were adopted for the LVDS driver and receiver, respectively. Moreover, hardening techniques are used. The circuitry was designed and submitted for fabrication in a 0.18-µm CMOS Image Sensor (CIS) process at the end of 2011. The test results indicated that the LVDS driver and receiver can operate properly at the data rate of 1.2Gb/s with power consumption of 19.6mW.

The global electroweak fit at NNLO and prospects for the LHC and ILC

For a long time, global fits of the electroweak sector of the standard model (SM) have been used to exploit measurements of electroweak precision observables at lepton colliders (LEP, SLC), together with measurements at hadron colliders (Tevatron, LHC) and accurate theoretical predictions at multi-loop level, to constrain free parameters of the SM, such as the Higgs and top masses. Today, all fundamental SM parameters entering these fits are experimentally determined, including information on the Higgs couplings, and the global fits are used as powerful tools to assess the validity of the theory and to constrain scenarios for new physics. Future measurements at the Large Hadron Collider (LHC) and the International Linear Collider (ILC) promise to improve the experimental precision of key observables used in the fits. This paper presents updated electroweak fit results using the latest NNLO theoretical predictions and prospects for the LHC and ILC. The impact of experimental and theoretical uncertainties is analysed in detail. We compare constraints from the electroweak fit on the Higgs couplings with direct LHC measurements, and we examine present and future prospects of these constraints using a model with modified couplings of the Higgs boson to fermions and bosons.

The Production of Ξbb at the Photon Collider

The inclusive production of the doubly heavy baryon Ξbb is investigated with a polarized and unpolarized photon collider. The bb pair in both a color triplet and sextet has been considered to transform into Ξbb. The results indicate that the contribution from the color sextet is about 8% for Ξbb production. For the international linear collider collision energy ranging from 91 GeV to 1000 GeV, the total cross section of Ξbb shows a downtrend, i.e., the production of Ξbb has the maximal rate at √S = 91 GeV. Our results indicate that the initial beam polarization may be an important asset for the production of Ξbb. At some collision point, the production rate of Ξbb can be increased by about 17% with an appropriate choice of the initial beam polarization.

A hadronic calorimeter with Glass RPC as sensitive medium

The SDHCAL technological prototype is a 1 × 1 × 1.3 m3 high-granularity Semi-Digital HadronicCALorimeter using Glass Resistive Plate Chambers as sensitive medium.It is one of the two HCAL options considered by the ILD Collaborationto be proposed for the detector of the future International LinearCollider project. The prototype is made of up to 50 GRPC detectors of1 m2 size and 3 mm thickness each with an embedded semi-digitalelectronics readout that is autotriggering and power-pulsed. The GRPCreadout is finely segmented into pads of 1 cm2. Measuredperformances of the GRPC and the full SDHCAL prototype in terms ofhomogeneity, low noise and energy resolution are presented in thisproceeding.

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.

Prospect for a study of Randall-Sundrum models from Higgs bosons decay at future colliders

In a class of Randall-Sundrum(RS) models, matter fermions and gauge bosons live in a five-dimensional bulk, while the Higgs boson lives in a four-dimensional visible brane. The Higgs boson can mix with a radion, by a Higgs-radion mixing term. It is difficult to directly discover the heavy Kaluza-Klein(KK) particles at the Large Hadron Collider(LHC), because the mass of the lightest KK particle is expected to be above 10 TeV to satisfy constraints from flavor changing neutral currents. Instead, the precision measurements of the Higgs sector at the high luminosity LHC(HL-LHC) and the International Linear Collider(ILC) is a promising way to observe the deviation originating from the Higgs-radion mixing and radiative corrections from the KK gauge bosons and matter fermions. For some cases, those effects are separately determined, providing valuable information on the model. We perform an extensive scan of the model parameters to see the expected deviations of the Higgs couplings. We also choose several reference points consistent with the current data to show the precision of the fundamental parameter measurements at the future colliders. We also study the radion-$Z$-$Z$ coupling in the model and discuss the role of the ILC for radion search.

Keynote: Electropolishing of Niobium Superconducting Radio Frequency Cavities in a Low-Viscosity, Water-Based, HF-Free Electrolyte: From Coupons to Cavities

Niobium superconducting radio frequency cavities (SRF) are required for the International Linear Collider as well as other high energy physics projects. In order for these cavities to achieve the required particle acceleration gradients, electropolishing is conducted as a final surface finishing operation. Conventional electropolishing of SRF cavities is based on the well-established viscous salt film theory [1] and utilizes a viscous electrolyte consisting of a mixture of sulfuric acid (95-98%) and hydrofluoric acid (49%), in a 9:1 volume ratio.[2] The HF is included to depassivate the niobium oxide film during electropolishing.[3]Based on prior surface finishing activities using pulse reverse waveforms in low viscosity aqueous electrolytes, we speculated that a new paradigm was evolving and could be applied to electropolishing of SRF cavities. Initial research funds were provided from the Small Business Innovation Research program to demonstrate the feasibility of electropolishing niobium coupons in aqueous electrolytes using “Bipolar EP.” Although coupon polishing was successful, further funding was not provided due at least in part to skepticism by the review community familiar with the conventional viscous salt film theory. Subsequently, the American Recovery and Reinvestment Act funded a high risk/high payoff project to demonstrate the bipolar EP process on single cell SRF cavities. The ARRA funds did not allow for mechanistic studies or preliminary experiments on curved sections representative of the SRF cavity geometry.Within these funding constraints, Faraday used guidelines and observations from 1”x1” and 3”x3” coupons to scale the bipolar EP process to single cell SRF cavities of ~1,800cm2 surface area. We recently reported these results at the 16th International Conference on RF Superconductivity in collaboration with Fermi National Accelerator Laboratory who declared that this cavity demonstrated the highest performance of any cavity previously processed at FNAL.The presentation will focus on our development activities from coupons to cavities and the evolution of key observations required to electropolish niobium.[4] These key observations on niobium coupons were used to guide the development of bipolar EP process parameters on single cell SRF cavities even while the detailed mechanistic aspects were not completely understood. We conclude that innovation requires a careful balance between current fundamental understandings combined with evolving observation which do not necessarily fit the current paradigm. The financial support of Faraday corporate, DOE P.O. No. 594128 and DOE Contract No. DE-SC0004588, and the technical support of Mr. Allan Rowe at Fermilab are acknowledged. [1] P.A. Jacquet Trans. Electrochem. Soc. 69, 629 (1936). [2] H. Tian, S. Corcoran, C. Reece, M. Kelly, J. Electrochem. Soc., 155, D563-568 (2008).[3] MacDougall, B. (1995), The Importance of Surface Oxide Films in Corrosion, Semiconductor and Environmental Research, Proceedings of the Symposium on High Rate Metal Dissolution Processes, Electrochemical Society Proceedings Vol. 95-19, Eds. M. Datta, B. MacDougall and J. Fenton, The Electrochemical Society, Pennington, NJ, pp 16-31.[4] Inman, M., E.J. Taylor and T.D. Hall, Electropolishing of Passive Materials in HF-Free Low Viscosity Aqueous Electrolytes, J. Electrochem. Soc., 160 (9), E94-E98, 2013.

Polarisation and beam energy measurement at a linear e+e− collider

The International Linear Collider (ILC) is a future electron/positroncollider at the energy frontier. Its physics goals are clearly focusedon precision measurements at the electroweak scale and beyond. Beamenergy and beam polarisation are two important beam parameters, whichneed to be measured and monitored to any possible precision. Wediscuss in this publication the foreseen concepts of beam energy andbeam polarisation measurement at the ILC.Two Compton polarimeters per beam line will determine the beampolarisation. The anticipated precision of this measurement amountsto Δ\U0001d4ab/\U0001d4ab = 2.5 × 10−3, which is achallenging goal putting highest demands on detector alignment andlinearity. Recent detector developments as well as a detectorcalibration technique are described, which allow for meeting theserequirements. The beam energy is measured before and after theinteraction point to a targeted precision of ΔE/E = 10−4. Thereby, the two foreseen concepts are introduced: anoninvasive energy spectrometer based on beam position monitors isplanned to be operated before the interaction region. Behind, asynchrotron radiation imaging detector will allow not only formeasuring the beam energy, but also gives access to the beam energyspread of the (disrupted) beam.

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