Electron-positron Linear Collider Research Articles

Model-independent determination of the top Yukawa coupling from LHC and ILC

We show how a measurement of the process pp-->t tbar H + X at the LHC and a measurement of the Higgs boson branching ratios BR(H-->b bar) and BR(H-->W+W-) at a future linear electron positron collider can be combined to extract a model-independent measurement of the top quark Yukawa coupling. We find that for 120 GeV < m_H < 200 GeV a measurement precision of 15% including systematic uncertainties can be achieved for integrated luminosities of 300 fb-1 at the LHC and 500 fb-1 at the LC at a centre-of-mass energy of 350 GeV.

Effects of the strong magnetic field on LED, extruded scintillator and MRS photodiode

The experimental results on the performance of the Metal/Resistor/Semiconductor (MRS) photodiode in the strong magnetic field of 4.4 T, and the possible impact of the quench of the magnet at 4.5 T on sensor's operation are reported. In addition, the experimental results on the performance of the extruded scintillator and WLS fiber, and various LEDs in the magnetic fields of 1.8 and 2.3 T, respectively, are detailed. The measurement method used is being described. The results of the work agree with the expectations that the LED, MRS and scintillator are not exhibiting sensitivity to the magnetic field presence. This result is essential for the design of the future electron–positron linear collider detector.

Effects of the mixing of scalar and pseudoscalar Higgs bosons in the process $$e^ + e^ - \to e^ + e^ - b\bar b$$ at a future linear electron-positron collider

The sensitivity of data on the process \(e^ + e^ - \to e^ + e^ - b\bar b\) at a future linear electron-positron collider to the deviation of the coupling of the Higgs boson to b quarks from the Standard Model predictions owing to the presence of a pseudoscalar Higgs boson state is analyzed for a collision energy of \(\sqrt s = 500 Gev\). The admixture of a new hypothetical pseudoscalar Higgs boson state in the \(Hb\bar b\) vertex is parametrized in the form mb/v(a + iγ5b). On the basis of an analysis of data on the process \(e^ + e^ - \to e^ + e^ - b\bar b\), it is shown that experiments at the future linear collider TESLA will make it possible to constrain the parameters Δa = a − 1 and b as −0.056 ≤ Δa ≤ 0.055 and −0.32 ≤ b ≤ 0.32, respectively.

High-power multimodeX-band rf pulse compression system for future linear colliders

We present a multimode $X$-band rf pulse compression system suitable for a TeV-scale electron-positron linear collider such as the Next Linear Collider (NLC). The NLC main linac operating frequency is 11.424 GHz. A single NLC rf unit is required to produce 400 ns pulses with 475 MW of peak power. Each rf unit should power approximately 5 m of accelerator structures. The rf unit design consists of two 75 MW klystrons and a dual-moded resonant-delay-line pulse compression system that produces a flat output pulse. The pulse compression system components are all overmoded, and most components are designed to operate with two modes. This approach allows high-power-handling capability while maintaining a compact, inexpensive system. We detail the design of this system and present experimental cold test results. We describe the design and performance of various components. The high-power testing of the system is verified using four 50 MW solenoid-focused klystrons run off a common 400 kV solid-state modulator. The system has produced 400 ns rf pulses of greater than 500 MW. We present the layout of our system, which includes a dual-moded transmission waveguide system and a dual-moded resonant line (SLED-II) pulse compression system. We also present data on the processing and operation of this system, which has set high-power records in coherent and phase controlled pulsed rf.

Search for lepton flavor violating [formula omitted] reactions with high energy muons

A deep inerastic scattering process μ N → τ X is discussed to study lepton flavor violation between muons and tau leptons. In supersymmetric models, the Higgs boson mediated diagrams could be important for this reaction. We find that at a muon energy ( E μ ) higher than 50 GeV, the predicted cross section significantly increases due to the contribution from sea b -quarks. The number of produced tau leptons can be O ( 10 4 ) at E μ = 300 GeV from 10 20 muons, whereas O ( 10 2 ) events are given at E μ = 50 GeV . Another promising possibility to search for the e N → τ X reaction at an electron-positron linear collider is also discussed. Searches for these reactions would be competitive with studies of rare tau decays and have potential to improve sensitivities to lepton flavor violation significantly.

Indirect Sensitivities to the Scale of Supersymmetry

Precision measurements, now and at a future linear electron-positron collider (ILC), can provide indirect information about the possible scale of supersymmetry. We illustrate the present-day and possible future ILC sensitivities within the constrained minimal supersymmetric extension of the Standard Model (CMSSM), in which there are three independent soft supersymmetry-breaking parameters m_{1/2}, m_0 and A_0. We analyze the present and future sensitivities separately for M_W, sin^2(theta_eff), (g-2)_mu, BR(b -> s gamma), BR(B_s -> mu+ mu-), M_h and Higgs branching ratios. We display the observables as functions of m_{1/2}, fixing m_0 so as to obtain the cold dark matter density allowed by WMAP and other cosmological data for specific values of A_0, tan beta and mu > 0. In a second step, we investigate the combined sensitivity of the currently available precision observables, M_W, sin^2(theta_eff), (g-2)_mu and BR(b -> s gamma), by performing a chi^2 analysis. The current data are in very good agreement with the CMSSM prediction for tan beta = 10, with a clear preference for relatively small values of m_{1/2} \sim 300 GeV. In this case, there would be good prospects for observing supersymmetry directly at both the LHC and the ILC, and some chance already at the Tevatron collider. For tan beta = 50, the quality of the fit is worse, and somewhat larger m_{1/2} values are favoured. With the prospective ILC accuracies the sensitivity to indirect effects of supersymmetry greatly improves. This may provide indirect access to supersymmetry even at scales beyond the direct reach of the LHC or the ILC.

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Electron-positron linear colliders have been under development since about 20 years ago and are the strongest candidates as future accelerators for high-energy physics. Two different technologies, normal and superconducting, have been competing. Regardless of the technology used, it was anticipated that the colliders would be too expensive to be afforded by one country or one region, and the decision was made to construct a single collider under international collaboration. The world high-energy physics community decided last summer that the next linear collider should be built utilizing the superconducting technology. Since then an international team has worked intensely studying the design of the collider. This article briefly describes the machine and summarizes the current status of the design.

A study of lepton flavor violating [formula omitted] reactions in supersymmetric models

We study a lepton flavor violating μN→τX reaction in deep inelastic scattering region in supersymmetric models. The contribution from the Higgs boson mediation could be important for this reaction. For that case, the cross section is constrained by the experimental limit of the pseudo-scalar coupling from τ→μη decays. We find that at a muon energy (Eμ) higher than 50 GeV, the predicted cross section increases significantly due to the contribution from sea b-quarks. As a result, with 1020 muons per year, at most a number of O(104) is expected for μN→τX events at Eμ=300GeV, whereas O(102) events are given at Eμ=50GeV. Furthermore, the μN→τX phenomenology, in particular that for the signal and backgrounds, is briefly discussed. Another promising possibility to search for the eN→τX reaction at an electron–positron linear collider is also discussed. Searches for these reactions would be competitive to studies of rare tau decays and have potential to improve sensitivities to lepton flavor violation significantly.

Ion backflow in the Micromegas TPC for the future linear collider

We present ion backflow measurements in a Micromegas (MICRO-MEsh GASeous detector) TPC device developed for the next high-energy electron–positron linear collider under study and a simple explanation for this backflow. A Micromegas micromesh has the intrinsic property to naturally stop a large fraction of the secondary positive ions created in the avalanche. It is shown that under some workable conditions on the pitch of the mesh and on the gas mixture, the ion feedback is equal to the field ratio (ratio of the drift electric field to the amplification field). Measurements with an intense X-ray source are in good agreement with calculations and simulations. The conclusion is that in the electric field conditions foreseen for the Micromegas TPC (drift and amplification fields, respectively, equal to 150–200 V/cm and 50–80 kV/cm) the expected ion backflow will be of the order of 2–3×10-3. In addition, measurements have been done in a 2 T magnetic field: as expected the ion backflow is not altered by the magnetic field.

PHYSICS OPPORTUNITIES WITH A TEV LINEAR COLLIDER

▪ Abstract We discuss the physics motivations for building a 500 GeV–1 TeV electron-positron linear collider. The state-of-the-art collider technologies and the physics-driven machine parameters are discussed. Some of the phenomena well suited to study at a linear collider are described, including Higgs bosons, supersymmetry, other extensions to the standard model, and cosmology.

Ion backflow in the Micromegas TPC for the future linear collider

We present ion backflow measurements in a Micromegas (MICRO-MEsh GASeous detector) TPC device developed for the next high-energy electron–positron linear collider under study and a simple explanation for this backflow. A Micromegas micromesh has the intrinsic property to naturally stop a large fraction of the secondary positive ions created in the avalanche. It is shown that under some workable conditions on the pitch of the mesh and on the gas mixture, the ion feedback is equal to the field ratio (ratio of the drift electric field to the amplification field). Measurements with an intense X-ray source are in good agreement with calculations and simulations. The conclusion is that in the electric field conditions foreseen for the Micromegas TPC (drift and amplification fields, respectively, equal to 150–200 V/cm and 50–80 kV/cm) the expected ion backflow will be of the order of 2–3 × 10 - 3 . In addition, measurements have been done in a 2 T magnetic field: as expected the ion backflow is not altered by the magnetic field.

Determining resonance parameters of heavy Higgs bosonsat a future linear collider

This study investigates the potential of an Electron-Positron Linear Collider for measuring resonance parameters of Higgs bosons beyond the mass range studied so far. The analysis is based on the reconstruction of events from the Higgs-strahlung process $\mathrm{e}^ + \mathrm{e}^-\to\mathrm{HZ}$ . It is shown that the total width $\Gamma_{tot}^{\mathrm{H}}$ , the mass m H and the event rate N can be measured from the mass spectrum in a model independent way. Also, the branching ratios BR H WW and BR H ZZ can be measured, assuming these are the only relevant Higgs decay modes. The simulation includes realistic detector effects and all relevant Standard Model background processes. Results are given for m H = 200-320 GeV assuming ${\cal \int\!\! L} = 500$ fb-1 integrated luminosity at a collision energy $\sqrt{s} = 500$ GeV.

Commissioning of the 34-GHz, 45-MW Pulsed Magnicon

A high-efficiency, high-power magnicon at 34.272 GHz has been designed and built as a microwave source to develop radio frequency (RF) technology for future multi-TeV electron-positron linear colliders. To develop this technology, this new RF source is being perfected for necessary tests of accelerating structures, RF pulse compressors, RF components, and to determine limits of breakdown and metal fatigue. The design of this high-power amplifier tube, as well as the first experimental results are presented.

Comparison Study of Electromagnet and Permanent Magnet Systems for an Accelerator Using Cost-Based Failure Modes and Effects Analysis

The next generation of particle accelerators will be one-of-a-kind facilities, and to meet their luminosity goals they must have guaranteed availability over their several decade lifetimes. The Next Linear Collider (NLC) is one viable option for a 1 TeV electron-positron linear collider, it has an 85% overall availability goal. We previously showed how a traditional failure modes and effects analysis (FMEA) of a SLAC electromagnet leads to reliability-enhancing design changes. Traditional FMEA identifies failure modes with high risk but does not consider the consequences in terms of cost, which could lead to unnecessarily expensive components. We have used a new methodology, "life cost-based FMEA", which measures risk of failure in terms of cost, in order to evaluate and compare two different technologies that might be used for the 8653 NLC magnets: electromagnets or permanent magnets. The availabilities for the two different types of magnet systems have been estimated using empirical data from SLAC's accelerator failure database plus expert opinion on permanent magnet failure modes and industry standard failure data. Labor and material costs to repair magnet failures are predicted using a Monte Carlo simulation of all possible magnet failures over a 30-year lifetime. Our goal is to maximize up-time of the NLC through magnet design improvements and the optimal combination of electromagnets and permanent magnets, while reducing magnet.

Resonant production of scalar diquarks at the next generation electron–positron colliders

We investigate the potential of TESLA and JLC/NLC electron–positron linear collider designs to observe diquarks produced resonantly in processes involving hard photons.

Instrumentation of the forward region of the TESLA detector

The expected beam-beam interaction at the proposed TESLA electron-positron linear collider has a significant impact on the design of the TESLA detector. Especially the instrumentation of the very forward region down to polar angles below 5 mrad will have to handle an immense background of electrons and positrons adding up to TeVs of energy deposition per bunch crossing. Instrumentation down to small angles is crucial not only for the measurement of the luminosity through Bhabha scattering, but also to maximize the hermeticity of the detector. Additionally these charged particles from beamstrahlung have to be measured as part of the feedback system of the TESLA accelerator and could also be used for beam diagnostics. The present design of the TESLA detector foresees two calorimeters in the forward region whose technologies have to meet the requirements regarding detector resolutions and radiation hardness. PACS: 29.40.Vj Calorimeters – 29.17.+w Electrostatic, collective, and linear accelerators – 41.85.Qg Beam analyzers, beam monitors, and Faraday cups

Supersymmetric seesaw model and lepton-flavor violation at a future electron-positron linear collider

We study lepton-flavor violating slepton production and decay at a future ${e}^{+}{e}^{\ensuremath{-}}$ linear collider in the context of the seesaw mechanism in minimal supergravity post CERN LEP benchmark scenarios. The present knowledge of the neutrino sector as well as improved future measurements are taken into account. We calculate the signal cross sections $\ensuremath{\sigma}{(e}^{\ifmmode\pm\else\textpm\fi{}}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{l}_{\ensuremath{\beta}}^{\ifmmode\pm\else\textpm\fi{}}{l}_{\ensuremath{\alpha}}^{\ensuremath{-}}{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{b}^{0}{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{a}^{0}),$ ${l}_{\ensuremath{\delta}}=e,\ensuremath{\mu},\ensuremath{\tau},$ $\ensuremath{\alpha}\ensuremath{\ne}\ensuremath{\beta},$ and estimate the main background processes. Furthermore, we investigate the correlations of these signals with the corresponding lepton-flavor violating rare decays ${l}_{\ensuremath{\alpha}}\ensuremath{\rightarrow}{l}_{\ensuremath{\beta}}\ensuremath{\gamma}.$ It is shown that these correlations are relatively weakly affected by the uncertainties in the neutrino data but are very sensitive to the model parameters. Hence, they are particularly well suited for probing the origin of lepton-flavor violation.

CPasymmetries in neutralino production ine+e−collisions

We study two CP sensitive triple-product asymmetries for neutralino production ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{i}^{0}{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{j}^{0}$ and the subsequent leptonic two-body decay ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{i}^{0}\ensuremath{\rightarrow}\mathcal{l}\ifmmode \tilde{}\else \~{}\fi{}\mathcal{l},$ $\mathcal{l}\ifmmode \tilde{}\else \~{}\fi{}$$\ensuremath{\rightarrow}{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}^{0}\mathcal{l},$ for $\mathcal{l}=e,\ensuremath{\mu},\ensuremath{\tau}.$ We calculate the asymmetries, cross sections and branching ratios in the minimal supersymmetric standard model with complex parameters $\ensuremath{\mu}$ and ${M}_{1}.$ We present numerical results for the asymmetries to be expected at a linear electron-positron collider in the 500 GeV range. The asymmetries can go up to 25%. We estimate the event rates which are necessary to observe the asymmetries. Polarized electron and positron beams can significantly enhance the asymmetries and cross sections. In addition, we show how the two decay leptons can be distinguished by making use of their energy distributions.

Achievement of [formula omitted] in the superconducting nine-cell cavities for TESLA

The Tera Electronvolt Superconducting Linear Accelerator (TESLA) is the only linear electron–positron collider project based on superconductor technology for particle acceleration. In the first stage with 500 GeV center-of-mass energy an accelerating field of 23.4 MV/ m is needed in the superconducting niobium cavities which are operated at a temperature of 2 K and a quality factor Q 0 of 10 10. This performance has been reliably achieved in the cavities of the TESLA Test Facility (TTF) accelerator. The upgrade of TESLA to 800 GeV requires accelerating gradients of 35 MV/ m . Using an improved cavity treatment by electrolytic polishing, it has been possible to raise the gradient to 35– 43 MV/ m in single cell resonators. Here we report on the successful transfer of the electropolishing technique to multi-cell cavities. Presently 4 nine-cell cavities have achieved 35 MV/ m at Q 0⩾5×10 9, and a fifth cavity could be excited to 39 MV/ m . In two high-power tests it could be verified that EP-cavities preserve their excellent performance after welding into the helium cryostat and assembly of the high-power coupler. One cavity has been operated for 1100 h at the TESLA-800 gradient of 35 MV/ m and 57 h at 36 MV/ m without loss in performance.

Formula omitted] QCD and [formula omitted] electroweak corrections to [formula omitted] production in γγ collision

We calculate the O(α s) QCD and O(α ew ) electroweak one-loop corrections in the Standard Model framework, to the production of an intermediate Higgs boson associated with t t ̄ pair via γγ fusion at an electron–positron linear collider (LC). We find the O(α s) QCD corrections can be larger than the O(α ew ) electroweak ones, with the variations of the Higgs boson mass m h and e + e − colliding energy s . Both corrections may significantly decrease or increase the Born cross section. The numerical results show that the relative corrections from QCD to the process e +e −→γγ→t t ̄ h 0 may reach 34.8%, when s =800 GeV and m h =200 GeV, while those from electroweak can be −13.1, −15.8 and −12.0%, at s =800 GeV, 1 TeV and 2 TeV, respectively.