Narrow Results

The Circular Electron Positron Collider (CEPC) as a Higgs factory was proposed in September 2013. The preliminary conceptual design report was completed in 2015.¹ The CEPC detector design was using International Linear Collider Detector — ILD² as an initial baseline. The CEPC calorimeters, including the high granularity electromagnetic calorimeter (ECAL) and the hadron calorimeter (HCAL), are designed for precise energy measurements of electrons, photons, taus and hadronic jets. The basic resolution requirements for the ECAL and HCAL are about 16%$\sqrt{E}$ (GeV) and 50%$\sqrt{E}$ (GeV), respectively. To fully exploit the physics potential of the Higgs, $W$, $Z$ and related Standard Model processes, the jet energy resolution is required to reach 3%–4%, or 30%/$\sqrt{E}$ (GeV) at energies below about 100 GeV. To achieve the required performance, a Particle Flow Algorithm (PFA) — oriented calorimetry system is being considered as the baseline design. The CEPC ECAL detector options include silicon–tungsten or scintillator–tungsten structures with analog readout, while the HCAL detector options have scintillator or gaseous detector as the active sensor and iron as the absorber. Some latest R&D studies about ECAL and HCAL within the CEPC working group is also presented.

In this paper we will give an introduction to the Circular Electron Positron Collider (CEPC). The scientific background, physics goal, the collider design requirements and the conceptual design principle of the CEPC are described. On the CEPC accelerator, the optimization of parameter designs for the CEPC with different energies, machine lengths, single ring and crab-waist collision partial double ring, advanced partial double ring and fully partial double ring options, etc. have been discussed systematically, and compared. The CEPC accelerator baseline and alternative designs have been proposed based on the luminosity potential in relation with the design goals. The CEPC sub-systems, such as the collider main ring, booster, electron positron injector, etc. have also been introduced. The detector and the MAchine-Detector Interface (MDI) design have been briefly mentioned. Finally, the optimization design of the Super Proton–Proton Collider (SppC), its energy and luminosity potentials, in the same tunnel of the CEPC are also discussed. The CEPC-SppC Progress Report (2015–2016) has been published.

The interaction region is designed to provide strong focusing at the interaction point. A local correction scheme is adopted to get a large momentum acceptance. The interaction region consists of several modular sections. This paper presents the optics design of each section and its optimization. As an example, the optics design for the CEPC single-ring scheme is presented.

The energy sawtooth will be significant in the future circular Higgs factory with beam energy as high as 120 GeV. For the partial double ring scheme, unlike the double ring scheme, the effects of energy sawtooth cannot be corrected by tapering the magnet strength with beam energy along the beamline. In this paper, the energy sawtooth effects in the partial double ring scheme and its mitigation methods are presented. As an example, the study of the energy sawtooth effects of the CEPC advanced partial double ring scheme is presented.

In the tracking of the future circular Higgs factories, significant reduction of dynamic aperture due to the synchrotron radiation has been observed. This paper will analyze the synchrotron radiation effects including the closed orbit and optics distortion, radiation damping and quantum excitation for the lattice of CEPC.

The electroweak phase transition can be made first order by extending the Standard Model (SM) Higgs sector with extra scalars. Here, we focus on the strong first-order electroweak phase transition (SFOEWPT) in the Type-II two Higgs doublet models (2HDMs). Through a parameter space scan, we find that SFOEWPT suggests upper limits on the masses of the heavy Higgs $m_{A∕H∕H^{\pm }}$, which is less than 1TeV. High-temperature expansion and Higgs vacuum uplifting are used for analytical understanding of our results. We find that sizeable loop corrections require $m_A\approx m_{H^{\pm }}>m_H$ to meet the SFOEWPT condition in the Type-II 2HDM. We also study the possibility of probing SFOEWPT at the one-loop level from Higgs and $Z$-pole precision measurements at future Higgs and $Z$ factories.

Machine learning has blossomed in recent decades and has become essential in many fields. It significantly solved some problems in particle physics — particle reconstruction, event classification, etc. However, it is now time to break the limitation of conventional machine learning with quantum computing. A support-vector machine algorithm with a quantum kernel estimator (QSVM-Kernel) leverages high-dimensional quantum state space to identify a signal from backgrounds. In this study, we have pioneered employing this quantum machine learning algorithm to study the $e^{+}{e}^{-}\to ZH$ process at the Circular Electron–Positron Collider (CEPC), a proposed Higgs factory to study electroweak symmetry breaking of particle physics. Using 6 qubits on quantum computer simulators, we optimized the QSVM-Kernel algorithm and obtained a classification performance similar to the classical support-vector machine algorithm. Furthermore, we have validated the QSVM-Kernel algorithm using 6-qubits on quantum computer hardware from both IBM and Origin Quantum: the classification performances of both are approaching noiseless quantum computer simulators. In addition, the Origin Quantum hardware results are similar to the IBM Quantum hardware within the uncertainties in our study. Our study shows that state-of-the-art quantum computing technologies could be utilized by particle physics, a branch of fundamental science that relies on big experimental data.

The Circular Electron Position Collider (CEPC) is a future $Z$ and Higgs bosons factory, which targets precision electroweak and Higgs measurements. The simulation, reconstruction, analysis chain has been established at CEPC. The detector design parameters were optimized according to several performances of key physical objects. The physics potential has been studied for the detector geometry CEPC_v1.

The Circular Electron Positron Collider (CEPC) as a Higgs factory was proposed in September 2013. The preliminary conceptual design report was completed in 2015. The CEPC detector design was using International Linear Collider Detector — ILD as an initial baseline. The CEPC calorimeters, including the high granularity electromagnetic calorimeter (ECAL) and the hadron calorimeter (HCAL), are designed for precise energy measurements of electrons, photons, taus and hadronic jets. The basic resolution requirements for the ECAL and HCAL are about 16% (GeV) and 50% (GeV), respectively. To fully exploit the physics potential of the Higgs, W, Z and related Standard Model processes, the jet energy resolution is required to reach 3%–4%, or 30%/ (GeV) at energies below about 100 GeV. To achieve the required performance, a Particle Flow Algorithm (PFA) — oriented calorimetry system is being considered as the baseline design. The CEPC ECAL detector options include silicon–tungsten or scintillator–tungsten structures with analog readout, while the HCAL detector options have scintillator or gaseous detector as the active sensor and iron as the absorber. Some latest R&D studies about ECAL and HCAL within the CEPC working group is also presented.