Future Electron-positron Colliders Research Articles

Muon beamtest results of high-density glass scintillator tiles

To achieve the physics goal of precisely measure the Higgs, Z, W bosons and the top quark, future electron-positron colliders require that their detector system has excellent jet energy resolution. One feasible technical option is the high granular calorimetery based on the particle flow algorithm (PFA). A new high-granularity hadronic calorimeter with glass scintillator tiles (GSHCAL) has been proposed, which focus on the significant improvement of hadronic energy resolution with a notable increase of the energy sampling fraction by using high-density glass scintillator tiles. The minimum ionizing particle (MIP) response of a glass scintillator tile is crucial to the hadronic calorimeter, so a dedicated beamtest setup was developed for testing the first batch of large-size glass scintillators. The maximum MIP response of the first batch of glass scintillator tiles can reach up to 107 p.e./MIP, which essentially meets the design requirements of the CEPC GSHCAL. An optical simulation model of a single glass scintillator tile has been established, and the simulation results are consistent with the beamtest results.

Monte Carlo programs for small-angle Bhabha scattering* *Supported by the Russian Science Foundation (project No. 22-12-00021)

Luminosity monitoring at colliders was investigated using Monte Carlo event generator and integrator for simulation of Bhabha scattering at low angles. Results are presented for center-of-mass energies of the Z boson resonance and at 240 GeV for the conditions of typical luminosity detectors. It is shown that bremsstrahlung events with extremely low electron scattering angles are relevant to match the precision tags of future electron-positron colliders.

Definition of tolerances and corrector strengths for the orbit control of the High-Energy Booster ring of the future electron-positron collider

After the discovery of the Higgs boson at the LHC, particle physics community is exploring and proposing next accelerators, to address the remaining open questions on the underlying mechanisms and constituents of the present universe. One of the studied possibilities is FCC (Future Circular Collider), a 100-km-long collider at CERN [1]. The feasibility study of this future proposed accelerator implies the definition of tolerances on magnets imperfections and of the strategies of correction in order to guarantee the target performances of the High Energy Booster ring. The efficiency of the correction scheme, used to control the orbit, directly bounds the corrector needs and magnet tolerances. Analytic formulae give a first estimation of the average RMS values of the required dipole correctors’ strengths and of the allowed magnets misalignments and field quality along the entire ring. The distribution of the correctors along the ring is simulated, in order to verify the quality of the residual orbit after the proposed correction strategy and to compare it with the analytical predictions. First specifications of the orbit correctors strength and tolerances for the alignment of the main elements of the ring are presented. The limits of the studied correction scheme and method are also discussed.

Single Transverse Spin Asymmetry as a New Probe of Standard-Model-Effective-Field-Theory Dipole Operators.

Electroweak dipole operators in the standard-model-effective-field theory (SMEFT) are important indirect probes of quantum effects of new physics beyond the standard model (SM), yet they remain poorly constrained by current experimental analyses for lack of interference with the SM amplitudes in constructing cross section observables. In this Letter, we point out that dipole operators flip fermion helicities and so are ideally studied through single transverse spin asymmetries. We illustrate this at a future electron-positron collider with transversely polarized beams, where such an effect exhibits as azimuthal cosϕ and sinϕ distributions which originate from the interference of the electron dipole operators with the SM and are linearly dependent on their Wilson coefficients. This new method can improve the current constraints on the electron dipole couplings by 1-2 orders of magnitude, without depending on other new physics operators, and can also simultaneously constrain both their real and imaginary parts, offering a new opportunity for probing potential CP-violating effects.

Search for Dark Photon in e+e− → A′A′ Using Future Collider Experiments

The Standard Model (SM) does not provide an information for 26% of dark matter of the universe. In the dark sector, dark matter is supposed to be linked with the hypothetical particles called dark photons that have similar role to photons in electromagnetic interaction in the SM. Besides astronomical observation, there are studies to find dark matter candidates using accelerators. In this paper, we searched for dark photons using future electron-positron colliders, including Circular Electron Positron Collider (CEPC)/CEPC, Future Circular Collider (FCC-ee)/Innovative Detector for Electron-positron Accelerator (IDEA), and International Linear Collider (ILC)/International Large Detector (ILD). Using the parameterized response of the detector simulation of Delphes, we studied the sensitivity of a double dark photon mode at each accelerator/detector. The signal mode is double dark photon decay channel, e+e− → A’A’, where A’ (dark photon with spin 1) decaying into a muon pair. We used MadGraph5 to generate Monte Carlo (MC) events by means of a Simplified Model. We found the dark photon mass at which the cross-sections were the highest for each accelerator to obtain the maximum number of events. In this paper we show the expected number of dark photon signal events and the detector efficiency of each accelerator. The results of this study can facilitate in the dark photon search by future electron-positron accelerators.

Design, construction and commissioning of a technological prototype of a highly granular SiPM-on-tile scintillator-steel hadronic calorimeter

The CALICE collaboration is developing highly granular electromagnetic and hadronic calorimeters for detectors at future energy frontier electron-positron colliders. After successful tests of a physics prototype, a technological prototype of the Analog Hadron Calorimeter has been built, based on a design and construction techniques scalable to a collider detector. The prototype consists of a steel absorber structure and active layers of small scintillator tiles that are individually read out by directly coupled SiPMs. Each layer has an active area of 72 × 72 cm^2 and a tile size of 3 × 3 cm^2. With 38 active layers, the prototype has nearly 22,000 readout channels, and its total thickness amounts to 4.4 nuclear interaction lengths. The dedicated readout electronics provide time stamping of each hit with an expected resolution of about 1 ns. The prototype was constructed in 2017 and commissioned in beam tests at DESY. It recorded muons, hadron showers and electron showers at different energies in test beams at CERN in 2018. In this paper, the design of the prototype, its construction and commissioning are described. The methods used to calibrate the detector are detailed, and the performance achieved in terms of uniformity and stability is presented.

Comprehensive dynamic numerical simulation of cooling process for a 1.3GHz 9-cell superconducting cavity based on different structures

As an indispensable component of X-ray free electron lasers and future ring electron-positron colliders, a 1.3 GHz 9-cell superconducting cavity provides higher acceleration voltage and higher RF power per unit length, and saves equipment space. During testing and operation, superconducting cavities often need to be cooled gradually from the ambient temperature (300 K) to the superconducting temperature (4.5 K or less). To avoid plastic deformation of materials and seal leaking caused by high thermal stress, the cooling rates in each stage and the temperature differences on the cavity must be properly controlled. Currently, a less effective manual control strategy is typically used, whose main limitations include a low level of automation, a high reliance on the experience of the operating personnel, and a fairly lengthy time due to low efficiency. In this paper, a 1.3 GHz 9-cell superconducting cavity and its helium vessel were taken as the research subjects, six different mechanical structures of the helium vessel were designed, and six different three-dimensional thermal-flow coupling models were established. For each structural model, the temperature distribution and cooling strategy were analyzed using fluid numerical simulation software. The influence of inlet parameters on the cooling process was analyzed, and the appropriate mechanical structure model was recommended. The results showed that: During the cooling process, the closer the superconducting cavity is to the inlet, the lower the temperature is. The cooling rate is faster in the early stage in which the temperature difference can be reduced by 50 % within the first 30 min. After experimental test verification, the total cooling time is about 650 min (10.8 h or so), and the deviation between the simulation results and the experimental test results is less than 7 %, which shows the simulation results can well predict the actual cooling process for 1.3 GHz 9-cell superconducting cavity. The research work in this paper can lay a good foundation for the further R&D status of the superconducting cavity.

Probing lepton flavor violation at Circular Electron-Positron Colliders

Lepton flavor violation is one of the cleanest probes of physics beyond the standard model. In this work, we explore the sensitivity of the process e+e− → τμ to new physics above the TeV scale at the proposed circular electron-positron colliders FCC-ee and CEPC. We compute the e+e− → τμ cross-section in the Standard Model Effective Field Theory and assess the relevant backgrounds. We compare our sensitivity projections to existing and expected constraints from tau decays and Z decays and find that the future electron-positron colliders provide competitive probes of new physics. We highlight the complementarity of searches for resonant e+e−→ Z → τμ production on the Z pole and searches for non-resonant e+e−→ τμ at higher center-of-mass energies.

Design and simulation of a cylindrical μRWELL inner tracker for the experiment at the Super Tau-Charm Facility

The Super Tau-Charm Facility (STCF) is a future electron-positron collider operating in a center-of-mass energy range from 2 to 7 GeV with a peak luminosity of 0.5 × 1035 cm-2s-1. A high-performance detector is required for the STCF experiment to meet the STCF physics goals. A low-material cylindrical inner tracker based on the micro-resistive well detector (μRWELL) is proposed for the STCF experiment. In this paper, the design of the μRWELL inner tracker is presented. A good balance between material budget, structural strength, and detector performance is achieved in the design where the material budget of the μRWELL inner tracker is estimated to be 0.29% X/X0, a 40% reduction w.r.t. that of the cylindrical gas electron multiplier (CGEM) detector used at the KLOE experiment. The hit position of the detector is reconstructed using an algorithm combing the micro-time projection chamber (μ-TPC) method and the charge center-of-gravity method. The detector performance was studied in detail using simulation with Garfield and Geant4. With the optimum working gas of Ar: CO2 = 85:15, this detector can obtain a spatial resolution better than 100 μm and 400 μm in 1 T magnetic field in rφ and beamline direction, respectively. The simulated momentum resolution and vertex resolution of the whole STCF tracking system including the μRWELL inner tracker and a large drift chamber can meet the requirements for the STCF detector, benefiting from the optimized inner tracker design.

Riding the Seesaw: what Higgsstrahlung may reveal about massive neutrinos

We investigate if the projected high-precision measurements of the cross section of the Higgsstrahlung process e^+ e^- rightarrow Zh at a future electron–positron collider can be utilised to indirectly probe the fermionic Seesaw models. We consider the two centre-of-mass energies sqrt{s}=240 GeV and 365 GeV, and compare the collider reaches to constraints from electroweak observables, probes of lepton flavour universality and the existing and prospective bounds from searches for lepton flavour violation. For the analysis we assume the limit of an exactly conserved lepton-number symmetry. We find that while any appreciable correction to the Higgsstrahlung cross section is already strictly constrained in the Type-I Seesaw model, effects of up to {mathcal {O}}(10%) are possible within Type-III Seesaw.

Heavy neutral leptons at beam dump experiments of future lepton colliders

A new beam dump experiment that utilizes the beam of future high energy electron-positron colliders could be an excellent avenue to search for dark sector particles due to its unprecedented high energy and intensity. We consider heavy neutral leptons (HNLs) as a specific example to demonstrate the sensitivity of searches for dark sector particles at future electron-positron collider beam dump experiments. This includes the study of the reach at the International Linear Collider (ILC), the Cool Copper Collider (C3), and the Compact Linear Collider (CLIC). We comprehensively examine the HNL production and detector acceptance at these electron beam dump experiments. We show that these experiments will probe regions of HNL parameter space, not yet probed by past experiments, as well as by future approved experiments. Our study also motivates a more detailed analysis of heavy meson productions in high-energy electron-nucleon collisions in thick targets.

Study of hybrid micropattern gaseous detector with CsI photocathode for Super Tau-Charm facility RICH

Super τ-Charm facility (STCF) is a future electron-positron collider operating in the τ-Charm energy region with the aim of studying hadron structure and spectroscopy. The baseline design of the STCF barrel particle identification (PID) detector, which covers momentum up to 2 GeV/c, is provided by a Ring Imaging Cherenkov Counter (RICH). The RICH features an approximately focusing design with liquid perfluorohexane sealed in a quartz container as the radiator and a hybrid combination of CsI-coated THGEMs and Micromegas as the photo-electron detector. A 16×16 cm2 prototype with a quartz radiator has been built and tested at DESY and stably operated with an effective gain of 105. In this paper, the design, performance, and reconstruction algorithm of RICH detectors are discussed.

Alysis of Laser-Plasma Based Electron-Positron Collider

Contemporarily, the collider plays a vital role in research and analysis for high energy physics, particle physics and astrophysics. However, conventional colliders usually need a large budget to operate as well as cover a large area for displacing the facility. With the rapid development of the laser techniques, the laser-plasma accelerator paves a path to accelerate particles in a compact way. On this basis, this paper will analyze the feasibility and recent progress for electron-positron collider realization via the concept of the laser-plasma acceleration. To be specific, the principles behind it will be analyzed initially. To be specific, an intense electromagnetic could make the plasma oscillated due to the pondermotive force, and the electron field created by the oscillation of the plasma could accelerate electrons to high energy. In addition, the possibility of applying laser plasma acceleration in to electron-positron collider is examined. These results shed light on guiding the further exploration of future electron-positron collider.

Probing a light dark sector at future lepton colliders via invisible decays of the SM-like and dark Higgs bosons

A renormalizable UV model for axionlike particles or hidden photons, which may explain the dark matter, usually involves a dark Higgs field, which is a singlet under the standard model (SM) gauge group. The dark sector can couple to the SM particles via the portal coupling between the SM-like Higgs and dark Higgs fields. Through this coupling, the dark sector particles can be produced in either the early Universe or the collider experiments. Interestingly, not only the SM-like Higgs boson can decay into the light dark bosons, but also a light dark Higgs boson may be produced and decay into the dark bosons in a collider. In this paper, we perform the first collider search for invisible decays by taking both the Higgs bosons into account. We use a multivariate technique to best discriminate the signal from the background. We find that a large parameter region can be probed at the International Linear Collider operating at the center-of-mass energy of 250 GeV. In particular, even when the SM-like Higgs invisible decay is a few orders of magnitude below the planned sensitivity reaches of the International Linear Collider and the high luminosity LHC, the scenario can be probed by the invisible decay of the dark Higgs boson produced via a similar diagram. Measuring the dark Higgs boson decay into the dark sector will be a smoking gun signal of the light dark sector. A similar search of the dark sector would be expected in, e.g., the Cool Copper Collider, the Circular Electron Positron Collider, the Compact Linear Collider, and the Future Circular electron-positron Collider.

Damping-ring-free electron injector proposal for future linear colliders

The current designs of future electron-positron linear colliders incorporate large and complex damping rings to produce asymmetric beams for beamstrahlung suppression. Here, we present the design of an electron injector capable of delivering flat electron beams with phase-space partition comparable to the electron-beam parameters produced downstream of the damping ring in the proposed International Linear Collider (ILC) design. Our design does not employ a damping ring but is instead based on cross-plane phase-space manipulation techniques. The performance of the proposed configuration, its sensitivity to jitter along with its impact on spin-polarization are investigated. The proposed paradigm could be adapted to other linear collider concepts under consideration and offers a path toward significant cost and complexity reduction.

Production of Exotic Particles in Electron-Positron Collisions

In this work, the results for cross sections of central exclusive exotic particles production in future linear electron-positron colliders are presented. These results show that the central production of charginos, dilatons, radions, axions and technipions can be measurable for the center-of-mass energies for these colliders. The results presented here, when compared with the production in hadronic colliders, have a smaller cross section, but with the advantage that the electron-positron collision does not have remnants coming from hadronic dissociation.

FPGA-based fast track reconstruction for the conceptual design of STCF MDC trigger

The Super Tau-Charm Facility (STCF) is a future high luminosity electron-positron collider proposed in China, with a peak luminosity greater than 0.5× 1035 cm2s-1 at center-of-mass energy of 4.0 GeV. The main drift chamber (MDC) is designed as the central tracker, which provides the charged particle information for the level-1 trigger. This paper presents an FPGA-based fast trigger algorithm with the function of finding the charged particle tracks and reconstructing their transverse momentum and azimuthal angle. It adopts a two-stage lookup-table-based pattern matching architecture. The prototype trigger logic was implemented in a Xilinx XCKU060 FPGA. Test results with simulated data suggest that the trigger efficiency of J/Ψ events is better than 96%, and the resolution in the reconstructed track's azimuthal angle at the interaction point is better than 12 mrad. The overall dead time is 24 ns and the total latency is 339 ns. All these performances meet the requirements of the MDC trigger in the current conceptual design stage of STCF project.

Two-photon physics at future electron-positron colliders* *The work of V.V.B. was supported in part by the Heisenberg-Landau Program

Two photon collisions offer a variety of physics phenomena that can be studied at future electron-positron colliders. Using the planned CEPC parameters as a benchmark, we consider several topics within two-photon collisions. With the full integrated luminosity, Higgs boson photoproduction can be reliably observed, and large statistics on various quarkonium states can be collected. The LEP results for the photon structure function and tau lepton anomalous magnetic moment can be improved by 1-2 orders of magnitude.

R&D of a Novel High Granularity Crystal Electromagnetic Calorimeter

Future electron-positron collider experiments aim at the precise measurement of the Higgs boson, electroweak physics and the top quark. Based on the particle-flow paradigm, a novel highly granular crystal electromagnetic calorimeter (ECAL) is proposed to address major challenges from jet reconstruction and to achieve the optimal EM energy resolution of around 2–3%/E(GeV) with the homogeneous structure. Extensive R&D efforts have been carried out to evaluate the requirements and potentials of the crystal calorimeter concept from sensitive detection units to a full sub-detector system. The requirements on crystal candidates, photon sensors as well as readout electronics are parameterized and quantified in Geant4 full simulation. Experiments including characterizations of crystals and silicon photomultipliers (SiPMs) are performed to validate and improve the simulation results. The physics performance of the crystal ECAL is been studied with the particle flow algorithm “ArborPFA” which is also being optimized. Furthermore, a small-scale detector module with a crystal matrix and SiPM arrays is under development for future beam tests to study the performance for EM showers.

BEEC2.0: An upgraded version for the production of heavy quarkonium at electron-positron collider

The event generator BEEC (Yang et al. (2013) [11]) was devoted to the simulation of heavy quarkonium production at an unpolarized electron-positron collider. We upgraded it here by adding the generation of quarkonium with polarized electron and positron beams. In addition, the production of color-singlet 2S-wave states were included. Several future electron-positron colliders with high luminosity have been under discussion in the past decade. Especially, their possibility of producing polarized beams is important for providing more insights into the underlying physics. This upgraded version offers a useful tool for the feasibility study on quarkonium from the experimental side. New version program summaryProgram title: BEEC version 2.0CPC Library link to program files:https://doi.org/10.17632/bvtwwm22tj.1Licensing provisions: GNU General Public License 3Programming language: FORTRAN 77/90Journal Reference of previous version: Comput. Phys. Commun. 184 (2013) 2848Does the new version supersede the previous version?: YesReasons for the new version: The proposed electron-positron colliders could possibly produce polarized beams, with which it would be helpful to provide more insights into the structure of the underlying physics in heavy quarkonium. Thus, it is essential to simulate the quarkonium production through polarized beams. In addition, the Bc(2S) state attracted more and more interests since its discovery, which makes it necessary to produce the 2S-wave excited states.Summary of revisions: Two polarized amplitudes of leptonic scattering are computed theoretically. The relevant codes of the formula are included in BEEC2.0. Meanwhile, new parameters for the 2S-excited states are also included.Nature of problem: Although PYTHIA can generate events for many processes, a dedicated event generator is also necessary. Especially, PYTHIA does not internally produce events with polarized beams. BEEC is implemented into PYTHIA as an external process for simulating heavy quarkonium events with high efficiency. Further hadronization and decay simulation can be done by using PYTHIA subroutine.Solution method: Two projection operators are used to calculate the polarized leptonic scattering amplitudes with the help of improved trace technology [1,2]. The code with option can generate events through unpolarized and polarized initial beams. In addition to the (QQ′¯)-quarkonium (Q,Q′=b,c) in color-singlet 1S-wave states, 1P-wave states, and the color-octet 1S-wave states in the last version, BEEC 2.0 also deal with the production of 2S-wave excited states within the framework of non-relativistic QCD [3].Additional comments including restrictions and unusual features: About the running time, it depends on which option one chooses to match PYTHIA when generating the heavy quarkonium events. Typically, for the production of the S-wave quarkonium states, if setting IDWTUP=1 (unweighted events), then it takes about 21 minutes on a 3.22 GHz Apple M1 Pro Processor machine to generate 105 events; if setting IDWTUP=3 (weighted events), it takes only ∼5 minutes to generate 105 events. While for the production of the P-wave quarkonium states, the time will be almost one hundred times longer than the case of the S-wave quarkonium.