Circular Electron Positron Collider Research Articles

Development of a Novel Highly Granular Hadronic Calorimeter with Scintillating Glass Tiles

Based on the particle-flow paradigm, a new hadronic calorimeter (HCAL) with scintillating glass tiles is proposed to address major challenges from precision measurements of jets at the future lepton colliders, such as the Circular Electron Positron Collider (CEPC). Tiles of high-density scintillating glass, with a high-energy sampling fraction, can significantly improve the hadronic energy resolution in the low-energy region (typically below 10 GeV for major jet components at Higgs factories). The hadronic energy resolution of single hadrons and the effects of key parameters of scintillating glass have been evaluated in the Geant4 full simulation, followed by the physics benchmark studies on the Higgs boson with jets in the final state. R&D efforts of scintillating glass materials are ongoing within a dedicated collaboration since 2021 with the aim to achieve a high light yield, a high density, and a low cost. Measurements have been performed for the first batches of scintillating glass samples including the light yield, emission and scintillation spectra, scintillation decay times, and cosmic responses. An optical simulation model of a single scintillating glass tile has been established to provide guidance in the development of scintillating glass. Highlights of the expected detector performance and the latest scintillating glass developments are presented in this contribution.

Design and Optimization of the Superconducting Quadrupole Magnet Q1a in CEPC Interaction Region

To study the properties of Higgs, scientists from the Institute of High Energy Physics have proposed to build the Circular Electron Positron Collider (CEPC) and published a conceptual design report in 2018. In order to improve the collision luminosity of CEPC, the upgrade of the final focus system in the interaction region is on-going. According to the latest physical requirements of superconducting magnets in the CEPC interaction region, a high gradient, double-aperture quadrupole magnet Q1a is required, which is 1.9 m from the interaction point. In this paper, we present the magnetic design of superconducting quadrupole magnet Q1a, and discuss the advantages and disadvantages of the three kinds of quadrupole coil structures, including cos2θ coil, CCT coil, and racetrack coil. Low-temperature superconductor NbTi is used in our magnet design process. In addition, optimization is performed to greatly reduce the weight of the magnet.

High-performance HV-CMOS sensors for future particle physics experiments — an overview

HV-CMOS (High Voltage-CMOS) sensors are emerging as a prime candidate for future tracking detectors that have extreme requirements on material budget, pixel granularity, time resolution and radiation tolerance. These sensors have the advantages of full monolithic structure, low manufacture cost, fast charge collection and high radiation tolerance. Confirmed and potential tracking applications in physics experiments include the Mu3e experiment, proton EDM searches, future upgrades of LHC (Large Hadron Collider) and CEPC (Circular Electron Positron Collider). The HV-CMOS group at Liverpool is doing generic R&D to push the boundaries of HV-CMOS sensors performance, especially in terms of single point resolution, fast-timing capability and radiation tolerance. This contribution gives an overview of the latest research by the Liverpool HV-CMOS group and presents the HV-CMOS prototypes developed in Liverpool.

Characterisation of HV-MAPS ATLASPix3 and its applications for future lepton colliders

HV-MAPS are a novel type of CMOS depleted active pixel sensors for ionizing particles, implemented in standard CMOS processes, that have been proposed in several future particle physics experiments for particle tracking. In depleted monolithic sensors, the sensor element is the n-well/p-substrate diode. The sensor matrix and the readout are integrated in one single piece of silicon and the electronics is embedded in shallow wells inside deep n-wells, isolated from the substrate. High voltage biasing increases the depth of the depletion region, improving sensor properties as signal amplitude, charge collection speed and radiation tolerance. ATLASPix3 is the first full reticle size high voltage Monolithic Active Pixel CMOS sensor, designed to meet the specifications of the outer layers of the ATLAS inner tracker (ITk). Its thin design, the excellent position resolution, high readout rate and high radiation tolerance make ATLASPix3 an ideal candidate for large-area tracking detector R&D of future collider experiments such as the Circular Electron Positron Collider (CEPC) silicon tracker.

A toy Monte Carlo simulation for the transverse polarization of high-energy electron beams

Transversely-polarized beams are heuristic to the mechanism of CP violation and explore new physics. Besides, the transverse-polarization monitoring is a key point for the beam energy calibration by the resonant depolarization technique. In the article, the transverse polarization measurement of a high-energy electron beam is performed by Monte Carlo simulation on the circular electron-positron collider. The principle based on the Compton back-scattering combining a deflection magnetic field is discussed in detail. The physical presentation of the analyzing power is used to fit the asymmetric distribution of scattered electrons, which is proportional to the transverse polarization. Furthermore, we develop an efficient algorithm that obtain this analyzing power function and use different strategies to measure the transverse polarization for cross-check. Our measurement method is theoretically suitable with a statistical error 1% within few tens of seconds in Z pole on the circular electron-positron collider. The total systematic uncertainties are controlled to be about 0.6% related to the magnetic field, the drift distance, the laser polarization, the beam energy spread and the related uncertainties of a position sensitive detector.

Performance of TPC detector prototype integrated with UV laser tracks for the circular collider

Several new experimental concepts in high-energy particle physics have been proposed in recent years. The physical goals include precisely measuring the properties of particles such as Higgs, Z and W, and even looking for signs of new physics at future colliders. To meet the evolving requirements for particle track detector, Time Projection Chamber (TPC) detector prototype integrated with a UV laser track system was developed for the main track detector at Circular Electron Positron Collider (CEPC). This prototype consists of 6 horizontal laser tracks around TPC detector chamber, a fast electronics readout of 1280 channels, a GEM detector with 200×200mm2 active area, and the DAQ system. The hit resolution, dE/dx resolution and drift velocity were studied by measuring and analyzing using the TPC prototype and UV laser tracks. The dE/dx resolution of the prototype was measured to be (8.9±0.4)%. Extrapolating this to CEPC TPC with 220 layers and longer track, the resolution was estimated to be (3.36±0.26)%. All results indicated that the TPC detector prototype integrated with UV laser tracks can work well.

Exploring fermionic multiplet dark matter through precision measurements at the CEPC * *The work of LQG and XJB is Supported by the National Natural Science Foundation of China (12175248); The work of JWW is Supported by the research grant "the Dark Universe: A Synergic Multi-messenger Approach" number (2017X7X85K) under the program PRIN 2017 funded by the Ministero dell'Istruzione, Universitàe della

New physics could be explored through loop effects using the precision measurements at the Circular Electron Positron Collider (CEPC) owing to its clean collision environment and high luminosity. In this paper, we focus on two dark matter models that involve additional electroweak fermionic multiplets. We calculate their one-loop corrections in five processes, i.e., , and , and investigate the corresponding signatures at the CEPC with the projected sensitivity. We observe that the detectable parameter regions of these processes are complementary. The combined analysis shows that the mass of dark matter in these two models can be probed up to and GeV, respectively, at a 95% confidence level.

Expected measurement precision with production at the CEPC * *Supported by the Innovative Research Program of IHEP (E2545AU210); CAS Center for Excellence in Particle Physics; Yifang Wang’s Science Studio of the Ten Thousand Talents Project; the CAS/SAFEA International Partnership Program for Creative Research Teams (H751S018S5); IHEP Innovation Grant (Y4545170Y2); Key Research Program of Frontier Sciences, CAS (XQYZDY-SSW-SLH002); Chinese Academy of

A search for the dimuon decay of the Standard Model Higgs boson is performed using Monte Carlo simulated events to mimic data corresponding to an integrated luminosity of 5.6 ab collected with the Circular Electron-Positron Collider detector in collisions at GeV. This study investigates the process, and the expected significance considering only the statistical uncertainty in the data for a background-only hypothesis for a Higgs boson with a mass of 125 GeV is found to be 6.1 , corresponding to a precision of 19%. The systematic impacts from the background Monte Carlo statistical fluctuations are estimated to be negligible. Moreover, the dependence of the measurement accuracy on the muon momentum resolution of the CEPC detector is investigated. It is found that the muon momentum resolution must be better than 204 MeV to discover the process at the nominal integrated luminosity. If the resolution is 100% worse than the designed parameter, the integrated luminosity must be greater than 7.2 ab to reach 5 significance.

Global fits of SUSY at future Higgs factories

In this work, we study the impact of electroweak and Higgs precision measurements at future electron-positron colliders on several typical supersymmetric models, including the constrained minimal supersymmetric Standard Model (CMSSM), nonuniversal Higgs mass generalizations (NUHM1, NUHM2), and the seven-dimensional minimal supersymmetric Standard Model (MSSM7). Using publicly available data from the $\mathsf{GAMBIT}$ community, we postprocess previous SUSY global fits with additional likelihoods to explore the discovery potential of Higgs factories, such as the Circular Electron Positron Collider (CEPC), the Future Circular Collider (FCC), and the International Linear Collider (ILC). We show that the currently allowed parameter space of these models will be further tested by future precision measurements. In particular, dark matter annihilation mechanisms may be distinguished by precise measurements of Higgs observables.

Optical and scintillation properties of aluminoborosilicate glass

The Circular Electron Positron Collider (CEPC) is a large international scientific facility proposed by the Chinese particle physics community. For the particle flow algorithms (PFA) oriented HCAL of the CEPC, an analog read-out option (AHCAL) is chosen in this regard. The proposal of silicon photomultiplier (SiPM) coupling with the glass scintillator as the detection unit HCAL is a new solution for the next generation calorimeter. The optical and scintilation characteristics of the aluminoborosilicate glass scintillator have been measured. When the wavelength is longer than 450 nm, the transmittance of the aluminoborosilicate glass is higher than 65%. In X-ray excited luminescence spectra, the integral intensity of the glass is 25.5% that of Bi4Ge3O12 (BGO) crystal. The energy resolution of the glass is approximately 27%. Moreover, the light yield of the glass is greater than 800 ph/MeV. The scintillating decay time of the fast and slow components is 262.10 ns (18%) and 1234.83 ns (82%), respectively. The difference between the scintillating and fluorescence decay time of the glass is explained by the luminescent mechanism. In addition, the afterglow of the glass was tested.

NLO QCD corrections to pseudoscalar quarkonium production with two heavy flavors in photon-photon collision

We calculate the next-to-leading order (NLO) QCD corrections to $\ensuremath{\gamma}+\ensuremath{\gamma}\ensuremath{\rightarrow}{\ensuremath{\eta}}_{c}+c+\overline{c}$, $\ensuremath{\gamma}+\ensuremath{\gamma}\ensuremath{\rightarrow}{\ensuremath{\eta}}_{b}+b+\overline{b,}$ and $\ensuremath{\gamma}+\ensuremath{\gamma}\ensuremath{\rightarrow}{B}_{c}+b+\overline{c}$ processes in the framework of nonrelativistic QCD factorization formalism. The cross sections at the SuperKEKB electron-positron collider, as well as the future collider like the Circular Electron Positron Collider, are evaluated. Numerical results indicate that the NLO corrections are significant, and the uncertainties in theoretical predictions with NLO corrections are reduced as expected. Due to the high luminosity of the SuperKEKB collider, the ${\ensuremath{\eta}}_{c}+c+\overline{c}$ production is hopefully observable in the near future.

Scintillator tile batch test of CEPC AHCAL

Hadron calorimeter (HCAL) is an essential sub-detector of the baseline detector system for Circular Electron Positron Collider (CEPC). We plan to build an Analog Hadron CALorimeter (AHCAL) prototype based on the Particle Flow Algorithm (PFA). The AHCAL of CEPC uses steel as the absorber and scintillator tiles read out by Silicon Photo-Multipliers (SiPMs) as the sensitive medium. The energy linearity and resolution of the calorimeter depend on the light yield uniformity of the sensitive medium. It is essential to qualify the entire detector production in order to select scintillator tiles with the uniformity of light yield within 10%. An automated batch test platform has been designed with 144 channels and an automated 3D servo motor. The paper summarizes the tests performed on more than 15000 scintillator tiles, and the SiPMs work at 59 V (overvoltage: 5 V). The measured light yield, corrected for the set-up response non-uniformity, is around 12.9 p.e. About 91.6% of scintillators (14219 pieces) are qualified within 10% of the light yield window.

Design and high-power test of 800-kW UHF klystron for CEPC

To reduce the energy demand and operation cost for circular electron positron collider (CEPC), the high efficiency klystrons are being developed at Institute of High Energy Physics, Chinese Academy of Sciences. A 800-kW continuous wave (CW) klystron operating at frequency of 650-MHz has been designed. The results of beam–wave interaction simulation with several different codes are presented. The efficiency is optimized to be 65% with a second harmonic cavity in three-dimensional (3D) particle-in-cell code CST. The effect of cavity frequency error and mismatch load on efficiency of klystron have been investigated. The design and cold test of reentrant cavities are described, which meet the requirements of RF section design. So far, the manufacturing and high-power test of the first klystron prototype have been completed. When the gun operated at DC voltage of 80 kV and current of 15.4 A, the klystron peak power reached 804 kW with output efficiency of about 65.3% at 40% duty cycle. The 1-dB bandwidth is ±0.8 MHZ. Due to the crack of ceramic window, the CW power achieved about 700 kW. The high-power test results are in good agreement with 3D simulation.

The mechanical design, fabrication and tests of dressed 650 MHz 2-cell superconducting cavities for CEPC

650 MHz 2-cell superconducting radio-frequency (SRF) cavities have been adopted for the collider ring of the Circular Electron Positron Collider (CEPC). By optimizing the wall thickness and geometry, the mechanical properties of the dressed cavity have been significantly improved with a focus on stress, tuning capabilities, pressure sensitivity, and Lorentz-force detuning, while microphonics and buckling were carefully monitored. Three cavities were later fabricated, post-processed and received vertical tests. The maximum unloaded quality factor (Q0) of the cavities has reached 3.2 × 1010 at 19.7 MV/m, which exceeded the design goal during operation. The favored small coefficient of Lorentz-force detuning was validated, too. Pressure sensitivity was measured and consistent with simulation prediction. Mounted with tuners, fundamental and high-order-mode (HOM) couplers, two dressed 650 MHz 2-cell cavities were finally integrated into a test cryomodule for a beam test facility. Both cavities were successfully tuned to the operating frequency of 650.000 MHz at 2.0 K. This article covers the mechanical aspects in the development and cryogenic tests of the 650 MHz 2-cell cavities.

Production of the B_c meson at the CEPC

In this paper, we make a detailed study on the production of the B_c, B_c^*, B_c(2,^1S_0), and B^*_c(2,^3S_1) mesons via the three planned running modes (Z, W, and H) at the future Circular Electron–Positron Collider (CEPC). The fragmentation-function and full nonrelativistic QCD approaches are adopted to calculate the production cross sections. Considering the excited states shall decay to the ground B_c state (e.g. 1^1S_0-state) with almost 100% probability, our numerical results show that up to next-to-leading order QCD corrections, there are about 1.4times 10^8B_c events to be accumulated via the Z mode (sqrt{s}=m_{_Z}) of the CEPC, but only about 1.6times 10^4 and 1.1times 10^4B_c events to be accumulated via the W (sqrt{s}=160,mathrm{GeV}) and H (sqrt{s}=240,mathrm{GeV}) modes, respectively. Since the Z mode is the best mode among the three planned modes of the CEPC for studying the production of the B_c, B_c^*, B_c(2,^1S_0), and B^*_c(2,^3S_1) mesons and the differential distributions of these mesons may be measured precisely at this mode, we further present the differential cross sections dsigma /(dz,dmathrm{cos}theta ) and dsigma /dz via the Z mode of the CEPC.

The future of particle physics and high energy accelerators—New acceleration mechanism possible?

<p indent="0mm">Recently, the future of particle physics and high energy accelerators aroused extensive attention from society. The view that current accelerators will soon be replaced by those based on the new acceleration mechanism, is widely spread. This view implies that next-generation high energy accelerators shall not be built until the new mechanism is ready. This paper introduces the near and mid-term science goals of particle physics, and the needed accelerators with the energy and luminosity requirements. By analyzing current status and possible future achievements of the new acceleration mechanism, or more precisely, plasma wakefield acceleration mechanism driven by laser or particle beams, we conclude that traditional accelerators will still be the main choice in the next <sc>20–30 years.</sc> First of all, we argue that studies such as neutrino physics, cosmic-rays physics, dark matter searches and dark energy studies may not rely on accelerators, but they do not represent the main-stream of particle physics. After the discovery of the Higgs boson, the particle physics community reached a consensus that our next priority is the study of Higgs couplings with all the other elementary particles. This study will not only test precisely the Standard Model, but also be the best probe to new physics beyond the Standard Model. For this purpose, a very high luminosity Higgs factory, based on the electron-positron collision, is needed. After a short introduction of different types of traditional accelerators and their related technologies, we conclude that linear electron (positron) accelerators are limited by their acceleration capabilities while their luminosity is much smaller than circular electron (positron) accelerators. Circular electron (positron) accelerators are limited by the synchrotron radiation hence their energy cannot reach <sc>300 GeV</sc> or above for a reasonable power consumption. Below this energy limit, circular colliders have advantages on luminosity, power consumption, cost, etc., over linear ones. Circular proton accelerators have very little synchrotron radiation, hence the acceleration goal is easy to achieve but the bending power of the magnet becomes the limit of energy. For linear proton accelerators, they have no advantages at all on energy, luminosity, power consumption, cost, etc., except at very low energies. From the above analysis, it is evident that the plasma-acceleration mechanism can only play a role on linear accelerators to improve acceleration capabilities if luminosity is not highly demanding. Obviously, even if plasma-accelerators are applicable, they are still not suitable for Higgs factories where the luminosity is a key while the energy is in the comfort zone of circular accelerators. Laser-driven accelerators are still far away to be applicable since their average power, power efficiency, beam quality and beam intensity are several orders of magnitude off, while beam-driven accelerators are off by a few factors to one order of magnitude. In addition, issues such as positron and proton acceleration mechanism, high efficiency multi-stage cascade acceleration need to be resolved and experimentally demonstrated. It is a common understanding that there are still <sc>20–30 years</sc> for the new acceleration mechanism to be a viable choice of high energy accelerators. However, plasma-based accelerators may find applications in irradiation, radiation imaging, free-electron laser, etc. in coming years. It may also be combined with traditional accelerators to form an injector. The future of high energy accelerators becomes then very clear: We shall build a circular electron-positron collider as a Higgs factory while actively working on R&amp;D for possible future very high energy (1–10 TeV) e⁺e^– linear colliders, as well as on high <italic>T</italic>_c superconducting technologies, in particular iron-based superconducting materials for future circular proton colliders.

Single top production via FCNC couplings at an $$e^{-}e^{+}$$ collider with center-of-mass energy $$\sqrt{s}=240$$ GeV

Aspects of top quark physics can be studied at a future Circular Electron-Positron Collider. In particular, flavor-changing neutral current interactions (FCNC) of the top quark can be studied even with a center-of-mass energy from \(\sqrt{s}\gtrsim m_t\) to \(\sqrt{s}=240\) GeV, through the production a single top quark in association with a charm quark, which can arise in several scenarios of new physics. We explore here this signal within the Left-Right Mirror Model, which is a Left-Right model that includes mirror fermions; this model is motivated as a possible solution to the strong CP problem and by its rich phenomenology. We find that for particular scenarios of the model parameters, which are in agreement with the most up-to-date experimental constraints, the signal coming from the process \(e^+e^-\rightarrow V \rightarrow tc\) (\(V=Z,\,Z^{\prime }\)) provides a detectable signal and thus, it can give evidence for FCNC interactions; in these scenarios, the mass of a new neutral gauge boson can be as high as \(m_{Z'}=7\) TeV.

Quality Factor Enhancement of 650 MHz Superconducting Radio-Frequency Cavity for CEPC

Medium-temperature (mid-T) furnace baking was conducted at 650 MHz superconducting radio-frequency (SRF) cavity for circular electron positron collider (CEPC), which enhanced the cavity unloaded quality factor (Q0) significantly. In the vertical test (2.0 K), Q0 of 650 MHz cavity reached 6.4 × 1010 at 30 MV/m, which is remarkably high at this unexplored frequency. Additionally, the cavity quenched at 31.2 MV/m finally. There was no anti-Q-slope behavior after mid-T furnace baking, which is characteristic of 1.3 GHz cavities. The microwave surface resistance (RS) was also studied, which indicated both very low Bardeen–Cooper–Schrieffer (BCS) and residual resistance. The recipe of cavity process in this paper is simplified and easy to duplicate, which may benefit the SRF community.

Design and development of the S-band high power test stand for multi-purpose applications at IHEP

A multipurpose S-band high-power test stand (HPTS) developed at the Institute of High Energy Physics (IHEP) of China is routinely used for radio-frequency (RF) conditioning of couplers and resonant structures, as well as other high-power experiments in the S-band frequency regime. The HPTS with a peak power of 230 MW was developed to meet requirements of various applications with multiple frequencies (2856 MHz/2998 MHz) and power levels (45 MW/50 MW/65 MW/80 MW) for different accelerator projects at the IHEP, e.g. the High Energy Photon Source (HEPS), Beijing Electron Positron Collider (BEPCII), Circular Electron Positron Collider (CEPC). This paper describes the design and implementation of the system in detail. The highlight of the HPTS is the impedance-matched design to accommodate different impedances, allowing a single pulse modulator to supply different types of klystron loads. The control system, developed under the Experimental Physics and Industrial Control System (EPICS), adopts a combination of Micro Telecommunications Computing Architecture (MTCA) based low-level RF system (LLRF) and programmable logic controller (PLC) based interlock unit controllers, and enables a real-time data acquisition and visualization. To ensure a high reliability and high-gradient RF power conditioning, the interlock unit integrates various protection features, like the short circuit load, high standing wave ratio, low vacuum, arcing detector, and abnormal dark current. It is worth mentioning that the entire conditioning procedure can be performed unattended automatically controlled. The test stand has been operated stably for more than 7,000 hours for many rounds of high-power RF conditioning with different power/frequency requirements, which indicates that the HPTS can provide a stable, reliable, and automatic high-power testing for the development of S-band related devices.

Unraveling the pion light-cone distribution function in the CEPC era

The light-cone distribution amplitude (LCDA) encapsulates the nonperturbative information of the hadronic states in hard exclusive reactions. The envisioned Circular Electron Positron Collider (CEPC) has the potential to access the pion LCDA at an unprecedented level of accuracy with its clean background, broad energy range, high luminosity and precision measurements. Such knowledge can not only deepen our understanding of the composite hadron structure, but also provide new insights for exploring the intricate structures of the underlying non-abelian gauge theory (QCD).