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Suppression of longitudinal coupled-bunch instabilities with RF feedback systems in CEPC main ring

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辐射探测技术与方法(英文) 2023年第2期7卷 210-219页

作者： Hang Zhu Tianmu Xin Jiyuan Zhai Jianping Dai The Institute of High Energy Physics The Chinese Academy of SciencesBeijingChina University of Chinese Academy of Sciences Beijing100049China

Background Circular electron positron collider(CEPC)is a 100-km electron positron collider proposed by IHEP.The longitudinal coupled-bunch instability(LCBI)of CEPC main ring operating to study the Z particle(Z machine)may be a limiting factor of CEPC and needs to be considered seriously.Purpose The purposes of this paper are to calculate the LCBI caused by the fundamental mode of superconducting RF cavities in CEPC main ring,which is the most critical impedance,and to complete the design of the RF feedback systems suitable for CEPC,whose specifications can suppress the LCBI to a manageable level.Methods The LCBI growth rate in the CEPC main ring is calculated in the frequency domain.Two kinds of RF feedback,i.e.,direct feedback and one-turn delay feedback,are simulated with the program to suppress the LCBI.And according to the suppression effect of LCBI growth rate after adding RF feedback,the required design parameters are given.Results Two operation conditions of Z machine have severe LCBI without suppression,and dozens of longitudinal modes are unstable.Only the direct RF feedback is needed to suppress LCBI in the case of Z-30 MW,while both the direct RF feedback with maximum gain and one-turn feedback are needed in the case of Z-50 MW.The LCBI growth rates can be reduced to the order of half frequency of the synchronous oscillation.Conclusion The LCBI of CEPC Z machine has been studied.Selecting appropriate feedback RF feedback can reduce the LCBI to an acceptable value that bunch by bunch feedback can suppress.

关键词： CEPC Beam loading Coupled-bunch mode LCBI Impedance of fundamental mode RF feedback

Estimation of the radiation backgrounds in the CEPC vertex detector

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Radiation Detection Technology and Methods 2022年第2期6卷 170-178页

作者： Wei Xu Haoyu Shi Hongbo Zhu Ke Li Sha Bai Xinchou Lou Institute of High Energy Physics Chinese Academy of SciencesBeijing 100049China School of Physics Zhejiang UniversityHangzhou 310058China Department of Physics University of WashingtonSeattleWA 98195USA

Background The Circular Electron-Positron Collider(CEPC)is aimed for precision measurements of the Higgs boson properties and the electroweak parameters.The achievable precision will be largely dependent on the controlled level of radiation backgrounds,which requires an optimized design of the interaction region to assure the optimal performance of both the accelerator and the detectors.Purpose In this article,the latest results on the radiation backgrounds are reported based on the accelerator parameters and the detector design presented in the CEPC conceptual design reports.Method For the different sources of radiation backgrounds,simulation steps consisting of generation,tracking,and detector simulation were performed.Radiation backgrounds from the processes of synchrotron radiation,pair production,radiative Bhabha scattering,beam gas Bremsstrahlung scattering,and beam thermal photon scattering were considered for the accel-erator operating at the different centre-of-mass energies(HZ threshold,WW threshold,and Z pole).Possible mitigation methods of masks and/or collimators were introduced to suppress the radiation backgrounds,together with the careful opti-mization of the interaction region design.With the improved tracking methods during simulation,the accuracy and reliability of the results were improved.In addition,the radiation backgrounds on the CEPC vertex detector were estimated,and the pair-production was found to be the most important source.Result In the worst case of operation at the Z pole,the vertex detector would have to withstand a total ionization dose of 5.6 Mrad per year and a non-ionization energy loss(shown in 1 MeV neutron equivalent)of 1.06×10^(13)n_(eq)/cm^(2)per year.

关键词： CEPC Interaction region Beam-induced background Vertex detector

Investigation of spin rotators in CEPC at the Z-pole

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Radiation Detection Technology and Methods 2022年第4期6卷 490-501页

作者： Wenhao Xia Zhe Duan Jie Gao Yiwei Wang Key Laboratory of Particle Acceleration Physics and Technology Institute of High Energy PhysicsChinese Academy of Sciences19B Yuquan RoadBeijing 100049China University of Chinese Academy of Sciences 19A Yuquan RoadBeijing 100049China

Purpose Longitudinal polarization is an important design aspect of the future 100 km-scale Circular Electron Position Collider(CEPC).Spin rotators are needed in the CEPC collider rings to make the beam polarization along the longitudinal direction at the interaction points(IPs).This paper focuses on the design of spin rotators for CEPC at the Z-pole(45.6 GeV).Methods The design of spin rotators in the CEPC at the Z-pole is based on solenoidmagnets and horizontal bending magnets sections.The coupling of transverse motion introduced by solenoids is compensated with quadrupole lenses.Adjustments have been made to the layout to implement the spin rotators into the collider rings.Results Longitudinal polarized beam can be achieved at the IPs with the spin rotators.High degree of polarization is attainable,while the effect of spin rotators on orbital motion is acceptable.The detailed simulation results will be presented.Conclusion A solenoid-based spin rotator configuration is designed and integrated into the CEPC collider ring lattice.According to the simulation results,the polarization requirements can be satisfied.

关键词： Beam polarization Spin rotator Electron storage ring CEPC Z-pole

Implementation and verification of the CEPC baseline tracker using a modern track reconstruction software

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Radiation Detection Technology and Methods 2023年第3期7卷 392-398页

作者： Yebo Chen Yubo Han Gang Li Linghui Wu Shuiting Xin Jin Zhang Hongbo Zhu Institute of High Energy Physics Chinese Academy of SciencesBeijing 100049China University of Chinese Academy of Sciences Beijing 100049China Deutsches Elektronen-Synchrotron(DESY) Notkestrasse 8522607 HamburgGermany School of Science Shenzhen Campus of Sun Yat-sen UniversityShenzhen 518107China School of Physics Zhejiang UniversityHangzhou 310058China

Purpose A high-performance tracking system will be crucial for the realization of the full physics potential of the Circular Electron Positron Collider(CEPC)project.Abaseline tracker has been proposed in the Conceptual Design Report and requires detailed studies of the layout geometry and comprehensive understanding of its tracking performance.Methods A Common Tracking Software(ACTS)is an experiment-independent software package and introduced for the track reconstruction for particle and nuclear physics experiments.The CEPC baseline tracker geometry has been implemented in ACTS,and its tracking performance has been evaluated with the provided track finding and fitting algorithms based on the truth tracking method.Results and Conclusion The tracking geometry implemented in ACTS,including the sensitive elements and simplified material distribution,has been validated.The track parameter resolutions obtained with ACTS are consistent with the full simulation results over the momentum range under investigation.ACTS has proven to be an excellent platform for the tracking performance evaluation and the tracker layout optimization.

关键词： CEPC Baseline tracker ACTS Truth tracking

Conceptual design of the CEPC dumping system

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辐射探测技术与方法(英文) 2023年第2期7卷 220-226页

作者： Guangyi Tang Qiongyao Liu Haoyu Shi Xiaohao Cui Zhongjian Ma Institute of High Energy Physics Chinese Academy of SciencesBeijing100049China

Background The circular electron–positron collider(CEPC)is a double-ring collider proposed by Chinese scientists.It will be operated at centre-of-mass energy of 240,90,160 GeV and maybe also 360 GeV.Purpose The total energy stored in the collider is up to 20 MJ.It is important to extract beams safely and not to damage the dump.In this paper,a dumping system including dilution kickers and absorber core with iron shielding is discussed.Methods The Monte Carlo code FLUKA is used to obtain the deposited energy and dose-equivalent distributions.The temperature rises are calculated assuming no heat conduction.Results Compared with the melting point and upper limit of dose equivalent,the magnets parameters are determined and the dimensions of the core and shielding are optimized.Conclusion The design of the dumping system meets the requirement that the energy stored in the collider can be absorbed safely.

关键词： CEPC Dumping system FLUKA Temperature rise Dose equivalent

Mechanical design of an ultra-light vertex detector prototype for CEPC

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Radiation Detection Technology and Methods 2022年第2期6卷 159-169页

作者： Jinyu Fu Zhijun Liang Hao Zeng Gang Li Mingyi Dong Huamin Qu Joao Guimaraes da Costa Institute of High Energy Physics Chinese Academy of SciencesBeijing 100049China State Key Laboratory of Particle Detection and Electronics.Institute of High Energy Physics Chinese Academy of SciencesBeijing 100049China University of Chinese Academy of Sciences Beijing 100049China

Background The Circular Electron Positron Collider(CEPC)is a large international scientific facility proposed to study the Higgs boson in great detail.It requires state-of-the-art detectors,including extremely precise vertexing and tracking devices,such as a silicon vertex detector.Purpose Silicon vertex detector with the precision required by the CEPC has never been built before and needs extensive research and development.This paper describes the mechanical design of a vertex detector prototype being built to explore the required technologies and the major challenges.Methods The exceptional high spatial resolution of the CEPC vertex detector is achievable only with a detector of extremely low mass to limit particle scattering.This paper proposes a mechanical design for the vertex detector prototype,highlighting the choice of low-mass materials,the analysis of support structures,the solution of detector cooling issues,and the drafts of procedures for detector assembly.Results The ultra-light support of the ladder(a structural unit of the CEPC vertex detector prototype),which is mainly made of carbon fiber reinforced polymer composite,has been designed.The fabrication process has also been verified.Global supporting and cooling method of the vertex detector prototype has been designed and chosen with results from finite element analysis and computational fluid dynamics simulations.Complete assembly and installation schemes for the prototype have been developed,and the respective tooling has also been designed.The performance of the vertex detector prototype,using this low-mass mechanical structure,was demonstrated with fast simulation to closely meet the CEPC physics requirement.

关键词： CEPC Silicon detector Mechanical design Carbon fiber reinforced polymer

Analysis of B_(c)→τν_(τ) at CEPC

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Chinese Physics C 2021年第2期45卷 39-47页

作者：郑太范徐吉曹璐于丹王伟 Soeren Prell 张若筠阮曼奇 School of Physics Nanjing UniversityNanjing 210023China INPAC SKLPPCMOE KLPPCSchool of Physics and AstronomyShanghai Jiao Tong UniversityShanghai 200240China Physikalisches Institut der Rheinischen Friedrich-Wilhelms-Universität Bonn 53115 BonnGermany Institute of High Energy Physics Beijing 100049China Department of Physics and Astronomy Iowa State UniversityAmesIAUSA

Precise determination of the B_(c)→τν_(τ) branching ratio provides an advantageous opportunity for under-standing the electroweak structure of the Standard Model,measuring the CKM matrix element |V_(cb)|,and probing new physics models.In this paper,we discuss the potential of measuring the process B_(c)→ τν_(τ)withτdecaying leptonically at the proposed Circular Electron Positron Collider(CEPC).We conclude that during the Z pole opera-tion,the channel signal can achieve five-σsignificance with~10^9 Z decays,and the signal strength accuracies for B_(c)→τν_(τ) can reach around 1%level at the nominal CEPC Z pole statistics of one tillion Z decays,assuming the total B_(c)→τν_(τ) yield is 3.6x 10^(6).Our theoretical analysis indicates the accuracy could provide a strong constraint on the general effective Hamiltonian for the b→cτν transition.If the total Be yield can be determined to 0(1%)level of accuracy in the future,these results also imply|V_(cb)| could be measured up to 0(1%)level of accuracy.

关键词： CEPC Flavor B_(c)meson

Search for invisible decays of the Higgs boson produced at the CEPC

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Chinese Physics C 2020年第12期44卷 1-8页

作者：谭雨航史欣 Ryuta Kiuchi 阮曼奇荆茂强于丹张凯栗娄辛丑莫欣李刚 Susmita Jyotishmati Institute of High Energy Physics Beijing 100049China School of Physical Sciences University of Chinese Academy of Science(UCAS)Beijing 100049China State Key Laboratory of Particle Detection and Electronics 19B Yuquan RoadShijingshan DistrictBeijing 100049China Department of Physics University of Texas at DallasTexas 75080-3021USA

The Circular Electron Positron Collider(CEPC),proposed as a future Higgs boson factory,will operate at a center-of-mass energy of 240 GeV and will accumulate 5.6 ab−1 of integrated luminosity in 7 years.In this study,we estimate the upper limit of BR(H→inv)for three independent channels,including two leptonic channels and one hadronic channel,at the CEPC.Based on the full simulation analysis,the upper limit of BR(H→inv)could reach 0.26%at the 95%confidence level.In the Stand Model(SM),the Higgs boson can only decay invisibly via H→ZZ∗→νν¯νν¯,so any evidence of invisible Higgs decays that exceed BR(H→inv)of the SM will indicate a phenomenon that is beyond the SM(BSM).The invariant mass resolution of the visible hadronic decay system ZH(Z→qq,H→inv)is simulated,and the physics requirement at the CEPC detector for reaching this is given.

关键词： CEPC invisible Higgs decays upper limit bosonmass resolution

The Higgs signatures at the CEPC CDR baseline

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Chinese Physics C 2019年第2期43卷 5-11页

作者：赵航朱永峰傅成栋于丹阮曼奇 Institute of High Energy Physics Chinese Academy of Sciences CAS Center for Excellence in Particle Physics Collaborative Innovation Center for Particles and Interactions University of Chinese Academy of Sciences

As a Higgs factory, the CEPC(Circular Electron-Positron Collider) project aims at precision measurements of the Higgs boson properties. A baseline detector concept, APODIS(A PFA Oriented Detector for the HIggS factory), has been proposed for the CEPC CDR(Conceptual Design Report) study. We explore the Higgs signatures for this baseline design with ■ Higgs events. The detector performance for reconstructing charged particles, photons and jets is quantified with H→μμ, γγ and jet final states, respectively. The resolutions of reconstructed Higgs boson mass are comparable for the different decay modes with jets in the final states. We also analyze the H→WW~* and ZZ* decay modes, where a clear separation between different decay cascades is observed.

关键词： CEPC Higgs boson full simulation