Linear Collider Research Articles

Probing extended Higgs sectors by the synergy between direct searches at the LHC and precision tests at future lepton colliders

We discuss a possibility that the parameter space of the two Higgs doublet model is significantly narrowed down by considering the synergy between direct searches for additional Higgs bosons at the LHC and its luminosity upgraded operation and precision measurements of the Higgs boson properties at future electron-positron colliders such as the International Linear Collider. We show that, in the case where the coupling constants of the discovered Higgs boson are slightly different from the predicted values in the standard model, most of the parameter space is explored by the direct searches of extra Higgs bosons, in particular for the decays of the extra Higgs bosons into the discovered Higgs boson, and also by the theoretical arguments such as perturbative unitarity and vacuum stability. This can be done because there appears an upper limit on the mass of the extra Higgs bosons as long as the deviation exists in the Higgs boson coupling. We also show that in the alignment limit where all the Higgs boson couplings take the standard model like values most of the parameter space cannot be excluded because most of the Higgs to Higgs decays are suppressed and also there is no upper limit on the masses from the theoretical arguments.

Searching for new light particles at the international linear collider main beam dump

We perform a feasibility study of a beam dump experiment at the International Linear Collider (ILC). To investigate the sensitivity to new light particles at the experiment, we consider models for axion-like particles (ALPs) and a light scalar particle coupled to charged leptons. For both models, we show that the detection sensitivity is almost an order of magnitude higher than other beam dump experiments in the small coupling region. For ALPs, it is shown that the ILC beam dump experiment is highly complementary to bounds from astrophysics. In addition, for the model of the scalar particle, the region favored by the muon $g-2$ experiment can be explored.

Tau g{-}2 at e^-e^+ colliders with momentum-dependent form factor

The deviation between the prediction based on the standard model and the measurement of the muon g{-}2 is currently at 3{-}4 sigma . If this discrepancy is attributable to new physics, it is expected that the new contributions to the tau g{-}2 even larger than those of muon due to its large mass. However, it is much more difficult to directly measure the tau g{-}2 because of its short lifetime. In this report, we consider the effect of the tau g{-}2 at e^-e^+ colliders using a model independent approach. Using the tau pair production channel at the Large Electron Position Collider (LEP), we have determined the allowed range for the new physics contribution of the tau g{-}2 assuming a q-square-dependence ansatz for the magnetic form factor. We also investigated the prospect at future e^+e^- colliders, such as International Linear Collider, the Compact Linear Collider, the Future Circular e^+e^- Collider, and Circular Electron Positron Collider, and determined the expected allowed range for the new physics contribution to the tau anomalous magnetic moment. The best limits are about 4{-}5 times more severe than the LEP one due to the beam polarization and the high luminosities at future colliders.

Phenomenology of a supersymmetric model inspired by inflation

The current challenges in high energy physics and cosmology are to build coherent particle physics models to describe the phenomenology at colliders in the laboratory and the observations in the universe. From these observations, the existence of an inflationary phase in the early universe gives guidance for particle physics models. We study a supersymmetric model which incorporates successfully inflation by a non-minimal coupling to supergravity and shows a unique collider phenomenology. Motivated by experimental data, we set a special emphasis on a new singlet-like state at 97,text {GeV} and single out possible observables for a future linear collider that permit a distinction of the model from a similar scenario without inflation. We define a benchmark scenario that is in agreement with current collider and Dark Matter constraints, and study the influence of the non-minimal coupling on the phenomenology. Measuring the singlet-like state with high precision on the percent level seems to be promising for resolving the models, even though the Standard Model-like Higgs couplings deviate only marginally. However, a hypothetical singlet-like state with couplings of about 20,% compared to a Standard Model Higgs at 97,text {GeV} encourages further studies of such footprint scenarios of inflation.

An integrated approach to understanding RF vacuum arcs

Although used in the design and costing of large projects such as linear colliders and fusion tokamaks, the theory of vacuum arcs and gradient limits is not well understood. Almost 120 years after the isolation of vacuum arcs, the exact mechanisms of the arcs and the damage they produce are still being debated. We describe our simple and general model of the vacuum arc that can incorporate all active mechanisms and aims to explain all relevant data. Our four stage model, is based on experiments done at 805 MHz with a variety of cavity geometries, magnetic fields, and experimental techniques as well as data from Atom Probe Tomography and failure analysis of microelectronics. The model considers the trigger, plasma formation, plasma evolution and surface damage phases of the RF arc. This paper also examines how known mechanisms can explain the observed sharp field dependence, fast breakdown times and observed surface damage. We update the model and discuss new features while also pointing out where new data would be useful in extending the model to a wider range of frequencies.

Measurements and modeling of stray magnetic fields and the simulation of their impact on the Compact Linear Collider at 380 GeV

The Compact Linear Collider (CLIC) targets a nanometer beam size at the collision point. Realizing this beam size requires the generation and transport of ultralow emittance beams. Dynamic imperfections can deflect the colliding beams, leading to a collision with a relative offset. They can also degrade the emittance of each beam. Both of these effects can significantly impact the luminosity of CLIC. In this paper, we examine a newly considered dynamic imperfection: stray magnetic fields. Measurements of stray magnetic fields in the Large Hadron Collider tunnel are presented and used to develop a statistical model that can be used to realistically generate stray magnetic fields in simulations. The model is used in integrated simulations of CLIC at 380 GeV including mitigation systems for stray magnetic fields to evaluate their impact on luminosity.

Energy and angular distributions of the bottom quark in the electron–positron annihilation e+e−→ bW+t̄

The distributions of the bottom quark in the process [Formula: see text] are considered at the [Formula: see text] energy corresponding to the first construction stage of the Compact Linear Collider. The cross-sections of [Formula: see text], as functions of the [Formula: see text]-quark energy and angle with respect to the direction of the electron beam, are derived and calculated. The effects of physics beyond the Standard Model are included via the modified [Formula: see text] and [Formula: see text] couplings which naturally appear in effective field theories. In addition to the cross-sections, the energy and angular asymmetries are calculated. The dependence of these observables on the [Formula: see text] energy is calculated, and features of this dependence are investigated.

Dark matter nature at electron-positron colliders: scalar or fermionic?

In this work, we investigated the possibility of identifying DM nature, at the future electron-positron colliders such as the International Linear Collider (ILC) and Compact Linear Collider (CLIC), at and 1 TeV, using the final state . For this purpose, we consider two models in which DM could be either a real scalar or a heavy right-handed neutrino (RHN). So we considered two parameter values sets for both models, and we defined and investigated the different recent experimental constraints. After that we define a set of kinematical cuts that suppress the background, and generate different distributions that are useful in identifying the DM nature. The use of polarized beams P(e −, e +) = [+0.8,−0.3] at the ILC makes the signal detection easier and the DM identification more clear, where the statistical significance gets enhanced by twice (five times) for scalar (fermionic) DM.

Simulation on graphite to copper joints in nuclear reactor applications by transient liquid phase bonding

Relating ceramics to metals furnish enduring difficulties in nuclear engineering industries. Arise out demanding need for advancement in suitable method for joining absorber made of graphite and radio frequency copper construction in Linear compact Collider. Transient liquid phase bonding is a favourable prospect to be used for connecting dissimilar materials with high level re-melt in temperature. This article describes the numerical affect of transient liquid phase bonding and brazing in ceramic/metal juncture and it is analyzed in the way employing the Finite Element Analysis (FEA) software. Aluminium foil was used as an interlayer material, due to its high wettability. Transient thermal analysis had been executed and stress dispersal was predicted by the developed numerical model. From the simulation studies, it is found that the stress obtained in the TLP process is only 47% of the maximum stress obtained during brazing and finally it enhances the effectiveness of linkage in graphite/copper joints.

Wakefield effects and mitigation techniques for nanobeam production at the KEK Accelerator Test Facility 2

The ATF2 beam line at KEK was built to validate the operating principle of a novel final-focus scheme devised to demagnify high-energy beams in future linear lepton colliders; to date vertical beam sizes as small as 41 nm have been demonstrated. However, this could only be achieved with an electron bunch intensity $\ensuremath{\sim}10%$ of nominal, and it has been found that wakefield effects limit the beam size for bunch charges approaching the design value of ${10}^{10}{e}^{\ensuremath{-}}$. We present studies of the impact of wakefields on the production of ``nanobeams'' at the ATF2. Wake potentials were evaluated for the ATF2 beam line elements and incorporated into a realistic transport simulation of the beam. The effects of both static (component misalignments and rolls, magnet strength errors and beam position monitor resolution) and dynamic (position and angle jitter) imperfections were included and their effects on the beam size evaluated. Mitigation techniques were developed and applied, including orbit correction, dispersion-free steering, wakefield-free steering, and interaction point tuning knobs. Explicit correction knobs to compensate for wakefield effects were studied and applied, and found to significantly decrease the intensity dependence of the beam size.

Main parameters of SppC-based “linac-ring eA” and “ring-ring µA” colliders

Concerning future lepton-nucleus colliders, International Linear Collider (ILC) and Plasma Wake Field Accelerator-Linear Collider (PWFA-LC) electrons in the order of 0.5 TeV and 5 TeV, respectively, colliding with Super proton–proton Collider (SppC)’s lead ions, are considered as “linac-ring eA” options. In addition, the 1.5 TeV option of the Muon Collider (MC) vs. 208Pb82+ ions of the SppC is also taken into account as a “ring-ring µA” collider. Luminosity values of the SppC-based eA and µA colliders are estimated. 3075 TeV lead parameters for the 100 km-circumference option of the SppC are taken into account to optimize luminosities of electron–nucleus and muon–nucleus collisions, keeping beam–beam effects and disruption in mind. It is shown that luminosities around 1030 cm−2 s−1 and 1032 cm−2 s−1 for eA and µA colliders, respectively, can be achieved by moderate upgrades of lepton and nucleus beam parameters.

High-gradient behavior of a dipole-mode rf structure

A normal-conducting, X-band traveling wave structure operating in the dipole mode has been systematically high-gradient tested to gain insight into the maximum possible gradients in these types of structure. Measured structure conditioning, breakdown behavior, and achieved surface fields are reported as well as a postmortem analysis of the breakdown position and a scanning electron microscope analysis of the high-field surfaces. The results of these measurements are then compared to high-gradient results from monopole-mode cavities. Scaled to a breakdown rate of ${10}^{\ensuremath{-}6}$, the cavities were found to operate at a peak electric field of $154\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ and a peak modified Poynting vector ${S}_{c}$ of $5.48\text{ }\text{ }\mathrm{MW}/{\mathrm{mm}}^{2}$. The study provides important input for the further development of dipole-mode cavities for use in the Compact Linear Collider as a crab cavity and dipole-mode cavities for use in x-ray free-electron lasers as well as for studies of the fundamental processes in vacuum arcs. Of particular relevance are the unique field patterns in dipole cavities compared to monopole cavities, where the electric and magnetic fields peak in orthogonal planes, which allow the separation of the role of electric and magnetic fields in breakdown via postmortem damage observation. The azimuthal variation of breakdown crater density is measured and is fitted to sinusoidal functions. The best fit is a power law fit of exponent 6. This is significant, as it shows how breakdown probability varies over a surface area with a varying electric field after conditioning to a given peak field.

Magnetic characterization of Mumetal® for passive shielding of stray fields down to the nano-Tesla level

The luminosity of a particle collider is an extremely crucial performance parameter describing its capability of producing interactions in the collision point. However, imperfections in a collider can lead to luminosity loss. Among different imperfections, an important one is stray magnetic fields. For the Compact Linear Collider (CLIC), a collider being considered as one of the main options in Europe after the Large Hadron Collider, simulations showed an unprecedented sensitivity of the machine to fields on the order of 0.1 nT. Hence, such tight constraints require special design considerations to prevent performance loss. Different shielding techniques are available in the literature, typically relying on an active shielding strategy and capable of reducing the magnetic field amplitudes down to the nano-Tesla level. However, measuring fields with such amplitudes is challenging by using state-of-the-art commercially available sensors and therefore, a passive shielding strategy, consisting in enveloping sections of the beamline with a magnetic shield, is a more attractive option. For CLIC, Mumetal®, a Ni–Fe alloy with advertised relative permeability above 100,000, was chosen. In this paper, the DC and AC magnetic characterization of two samples of Mumetal®, one annealed in its final form and the other one non-annealed is presented, showcasing how the annealing results in a boost of the magnetic permeability of more than order of magnitude. As a case study, the shielding performance of a 1-mm thin layer of Mumetal® enveloping CLIC’s beamline is estimated.

High-quality positron acceleration in beam-driven plasma accelerators

Author(s): Diederichs, S; Benedetti, C; Esarey, E; Osterhoff, J; Schroeder, CB | Abstract: Acceleration of positron beams in plasma-based accelerators is a highly challenging task. To realize a plasma-based linear collider, acceleration of a positron bunch with high-efficiency is required, while maintaining both a low emittance and a subpercent-level energy spread. Recently, a plasma-based positron acceleration scheme was proposed in which a wake suitable for the acceleration and transport of positrons is produced in a plasma column by means of an electron drive beam [Diederichs et al., Phys. Rev. Accel. Beams 22, 081301 (2019)PRABCJ2469-988810.1103/PhysRevAccelBeams.22.081301]. In this article, we present a study of beam loading for a positron beam in this type of wake. We demonstrate via particle-in-cell simulations that acceleration of high-quality positron beams is possible, and we discuss a possible path to achieve collider-relevant parameters.

Measurements of sub-nT dynamic magnetic field shielding with soft iron and mu-metal for use in linear colliders

There is an increasing need to shield beams and accelerator elements from stray magnetic fields. The application of magnetic shielding in linear colliders is discussed. The shielding performance of soft iron and mu-metal is measured for magnetic fields of varying amplitude and frequency. Special attention is given to characterise the shielding performance for very small-amplitude magnetic fields.

Prospects of measuring the branching fraction of the Higgs boson decaying into muon pairs at the International Linear Collider

The prospects for measuring the branching fraction of H rightarrow mu ^{+} mu ^{-} at the International Linear Collider (ILC) have been evaluated based on a full detector simulation of the International Large Detector (ILD) concept, considering centre-of-mass energies (sqrt{s}) of 250 GeV and 500 GeV with two different beam polarisation configurations of {mathcal {P}} (e^{-}, e^{+}) = (-,80{%}, +,30{%}) and (+,80{%}, -,30{%}). For both sqrt{s} cases, the two final states e^{+} e^{-} rightarrow qoverline{q}H and e^{+} e^{-} rightarrow nu overline{nu }H have been analyzed. For integrated luminosities of 2 hbox {ab}^{-1} at sqrt{s} =250 GeV and 4 hbox {ab}^{-1} at sqrt{s} =500 GeV, the combined precision on the branching fraction of H rightarrow mu ^{+} mu ^{-} is estimated to be 17%. The impact of the transverse momentum resolution for this analysis is also studied.

High radiation dose rates may improve cancer therapy

The ill-understood effect is gaining momentum and opening new avenues of research. CERN’s Compact Linear Collider and other particle accelerators are contributing.

Influence of Different Strain Hardening Models on the Behavior of Materials in the Elastic-Plastic Regime under Cyclic Loading.

In exact analyses of bodies in the elastic–plastic regime, the behavior of the material above critical stress values plays a key role. In addition, under cyclic stress, important phenomena to be taken into account are the various types of hardening and the design of the material or structure. In this process, it is important to define several groups of characteristics. These include, for instance, the initial area of plasticity or load which defines the interface between elastic and plastic deformation area. The characteristics also include the relevant law of plastic deformation which specifies the velocity direction of plastic deformation during plastic deformation. In the hardening condition, it is also important to determine the position, size and shape of the subsequent loading area. The elasto-plastic theory was used for the analysis of special compliant mechanisms that are applied for positioning of extremely precise members of the Compact Linear Collider (CLIC), e.g., cryomagnets, laser equipment, etc. Different types of deformation hardening were used to simulate the behavior of particular structural elements in the elastic–plastic regime. Obtained values of stresses and deformations may be used in further practical applications or as default values in other strain hardening model simulations.

Upgrade of the ILC Cryomodule

Results of testing modified components for the cryomodule of the International Linear Collider (ILC) are summarized. To reduce the ILC project cost, it is proposed to replace titanium cryomodule components with stainless steel (SS) ones. New bimetallic transitions Ti_SS, Nb_SS have been produced by a unique method based on explosion welding. Successive upgrading of these components to the latest version of the Nb/Ti/SS transition element has led to improvement of the ILC cryomodule. This new component resolves problems of residual stress, and its specific design prevents the possibility of a shift due to the difference in the linear expansion coefficients of the constituent metals. Leak tests with the He gas revealed no leaks at the background rate of 0.2x10-10atmxcc-1s. The test results are very encouraging. The up-to-date design of trimetallic Nb_Ti_SS element promises technologically simpler and less expensive manufacture. Investigations have shown that explosion welding allows unique trimetallic components to be made not only for cryogenic units of accelerators but also for laboratory equipment and for general engineering applications.

Double Higgs boson production and Higgs self-coupling extraction at CLIC

The Compact Linear Collider (CLIC) is a future electron–positron collider that will allow measurements of the trilinear Higgs self-coupling in double Higgs boson events produced at its high-energy stages with collision energies from sqrt{s} = 1.4 to 3 TeV. The sensitivity to the Higgs self-coupling is driven by the measurements of the cross section and the invariant mass distribution of the Higgs-boson pair in the W-boson fusion process, text {e}^{+}text {e}^{-}rightarrow {text {H}text {H}nu bar{nu }}. It is enhanced by including the cross-section measurement of ZHH production at 1.4 TeV. The expected sensitivity of CLIC for Higgs pair production through W-boson fusion is studied for the decay channels mathrm{b}bar{mathrm{b}}mathrm{b}bar{mathrm{b}} and mathrm{b}bar{mathrm{b}}mathrm{W}mathrm{W}^{*} using full detector simulation including all relevant backgrounds at sqrt{s} = 1.4 TeV with an integrated luminosity of mathcal {L} = 2.5 ab^{-1} and at sqrt{s} = 3 TeV with mathcal {L} = 5 ab^{-1}. Combining text {e}^{+}text {e}^{-}rightarrow {text {H}text {H}nu bar{nu }} and ZHH cross-section measurements at 1.4 TeV with differential measurements in text {e}^{+}text {e}^{-}rightarrow {text {H}text {H}nu bar{nu }} events at 3 TeV, CLIC will be able to measure the trilinear Higgs self-coupling with a relative uncertainty of -8% and +11% at 68% C.L., assuming the Standard Model. In addition, prospects for simultaneous constraints on the trilinear Higgs self-coupling and the Higgs-gauge coupling HHWW are derived based on the {text {H}text {H}nu bar{nu }} measurement.