CEPC顶点探测器风振分析与减振优化

顶点探测器是中国科学院高能所提出的首次应用于环形正负电子对撞机(CEPC)中的重要探测设备,基于顶点探测器探测精度与工作可靠性要求,顶点探测器的最大振幅需小于1µm,不满足要求将导致探测失效。采用了理论与数值模拟相结合的分析方法,利用梁的挠度计算公式分析了影响探测器刚性的主要因素,通过Fluent与瞬态结构耦合模拟计算危险工况下,空气流体激励中断再恢复时结构关键部位的振动响应,并对计算结果使用Origin可视化处理,结果表明流体流速为2 m/s时结构的最大振幅为1.29µm。通过对结构进行尺寸、形状和拓扑优化,并结合敏感性分析法分析优化措施效果,计算数据表明结构的刚度对增加两侧支撑厚度不敏感,增加支架高度对结构的刚度影响较大,形状和材料分布对结构稳定性具有决定性影响。

基于波形采样的CEPC电磁量能器读出单元测试系统

随着环形正负电子对撞机(Circular Electron Positron Collider,CEPC)方案的提出,由硅光电倍增管(Silicon Photomultiplier,SiPM)和塑料闪烁体组成的读出单元作为电磁量能器的预研方案之一,逐渐成为研究热点。在探测器预研阶段需要对读出单元性能进行充分研究,因此我们设计了一套自动化测试系统用于对读出单元进行测试、分析并改善其性能。利用DT5751波形采样插件、SiPM驱动电路板、步进电机、低压电源、继电器等完成硬件搭建,以LabVIEW为开发平台完成了软件的串行协议接口之间的通信,实现了读出单元的自动化测试,编写了相应的数据处理程序。在此基础上进行了SiPM刻度、闪烁体发光均匀性以及反射材料对光输出影响的研究。测试结果表明,ESR反射膜包裹的塑闪条具有最高的光输出,塑闪条耦合10μm像素SiPM的光输出为耦合25μm像素SiPM的三分之一。

CEPC直线加速器束流垃圾桶初步设计

束流垃圾桶的材料、结构、尺寸的正确设计对于确保高能环形对撞机(Circular Electron Positron Collider,CEPC)直线加速器的安全运行有重要意义。采用蒙特卡罗程序FLUKA,研究了概念设计阶段的CEPC直线加速器束流垃圾桶的初步设计方案,给出了作为吸收体设计依据的射程的不同计算方法及验证过程,以及屏蔽体部分的材料选择与总体屏蔽厚度的关系;计算过程中引入减方差技巧提高了计算结果的精确程度。

争议性科学事件中科学家间争论焦点研究

爆发于科学共同体成员之间的争论在进入公众视野后,争论焦点由认知要素向社会要素过渡,呈现出复杂的问题情境。为了厘清公共科学争论中持有不同观点的科学家群体的争论焦点,对王贻芳与杨振宁二人关于大型环形加速器−环形正负电子对撞机−超级质子对撞机(CEPC-SPPC)的争议性科学事件展开个案研究。根据编码数据梳理出双方争论的焦点是平等观念和经济问题,并对围绕上述焦点的科学话语展开文本分析。研究发现,在公共科学争论中,科学共同体成员之间争论的焦点本质是对多元主体利益的不同衡量方式,这种不同恰又体现为科学共同体成员能否超出科学共同体的立场来思考科学决策。

探究物质最基本的结构——从中微子和正负电子对撞谈起

首先对粒子物理的基本目标、实验方法、研究现状以及粒子标准模型进行了简要介绍。解释了为何寻求超出标准模型的物理信号是现阶段物理学研究的核心任务。接着着重介绍了首个在粒子物理实验中被证实的超出标准模型的实验信号、中微子振荡及其实验测量,以及通向新物理原理的探针——希格斯(Higgs)玻色子。最后,介绍了高能物理实验设施,特别是现有的北京正负电子对撞机项目和未来的环形正负电子对撞机项目。对于后者,除了明晰其突出的物理学意义和物理学性能,还阐述了其对科学技术的促进作用。

环形正负电子对撞机大型探测器超导磁体虹吸实验初步研究

对环形正负电子对撞机大型探测器超导磁体拟采用的低温虹吸实验进行了研究,通过液氮虹吸实验发现了倾斜角度对虹吸换热效果的影响。热虹吸管在15°时换热效果最佳(最大换热温差在4 K内),倾角增大,热虹吸管冷热端温差逐渐增大。对液氦虹吸实验装置进行设计和搭建,并进行了初步探索,研究发现蒸发侧热负荷为0.5 W时,管路换热温差为1.2 K,且装置本体漏热为0.5 W。

薄型较大面积THGEM气体探测器的研制

为满足环形正负电子对撞机项目配置的需要,研制了薄型较大面积THGEM气体探测器。该探测器工作时不需要额外的腔室,并且其厚度能达到8 mm,较原来的11 mm有明显减少。其有效面积为20 cm×20 cm,其增益在Ar/iC_4H_(10)(97/3)工作气体中能达到10~4倍,最好能量分辨为30%,增益均匀性能达到88.5%,探测器增益也呈现出较好的长期稳定性。

基于国产SiPM的量能器探测单元研究

为满足环形正负电子对撞机项目的需求,研究了基于国产SiPM的强子量能器探测单元。该探测单元由ESR反射膜包裹塑料闪烁体组成。实验测试表明:该探测单元的均匀性与MC模拟基本一致。均匀性为在平均值10%的偏差内的区域能达到93.75%。探测效率达到94.6%。良好的响应均匀性和探测效率结果表明了CEPC采用这种国产的SiPM基本可行。

特大型超高真空排气台的研制

为满足中科院高能物理研究所环型正负电子对撞机项目650 MHz/800 kW连续波速调管的超高真空排气需要,北方华创真空研制了由无油干泵和磁悬浮分子泵作为预抽系统,溅射离子泵作为主抽系统的特大型超高真空排气台。设备以温度和真空度作为主要工艺参数,对尺寸达到Φ1600 mm×5000 mm的连续波速调管进行高温真空烘烤排气,极限真空度优于8.0×10^-8 Pa;烘烤温度25~600℃连续可调,温区均匀性±5℃,具备充氮快速降温功能,整个工艺过程实现自动化控制。

仪器工业60年微观示踪复杂巨仪器的价值

2012年开始,3位大科学家争论中国该不该投千亿RMB于CEPC-SppC高能实验最复杂的"巨仪器"工程,引发国际前沿科学界的高度关注!5年后被权威1票否决。本文作者根据先后在乙方核-航天-通信电子、甲方BEPC-BES工程、丙方国标委核仪器、工业测控仪器标准化技术委员会各20年的实践,分析在技术经济状态空间中经历的一条60年Feynman路径积分,微观示踪科学与工业的内开放及其价值。

Study of CEPC performance with different collision energies and geometric layouts

The Circular Electron-Positron CoUider （CEPC） is one of the largest projects planned for high energy physics in China. It would serve first as a Higgs factory and then upgrade to a hadron collider. In this paper we give the 50 km and 100 km design for both single ring and double ring schemes, including Z boson, W boson and Higgs boson, by using an optimized method. Also, we give the potential of CEPC running at the Z and W poles. We analyse the relationship of luminosity with circumference and filling factor, which gives a way to evaluate the choice of geometry, and compare the nominal performances of CEPC-SPPC, LHC and FCC.

用于CEPC探测器超导磁体的液氮虹吸实验研究

概括了环形正负电子对撞机(CEPC)探测器超导磁体拟采用的虹吸冷却低温系统的研制背景,重点介绍了液氮虹吸实验平台的设计、组装及检漏。分别以氮气液化后的液氮填充相分离器的1/5和1/3体积的要求进行了两次实验,其常温常压下的体积分别为0.32m^3和0.47m^3。实验发现当充装量为0.32m^3时,蒸发侧加热功率达到10W后发生了烧干现象;充装量为0.47m^3时,蒸发侧加热功率达到20W后液氮回路仍循环良好,管路最大温差不到1K,管路温度分布均匀,未发生烧干现象。实验结果表明,氮气的充装量以及蒸发侧的加热功率是影响虹吸冷却效果的两个重要因素。

The Higgs signatures at the CEPC CDR baseline

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.

Cross section and Higgs mass measurement with Higgsstrahlung at the CEPC

The Circular Electron Positron Collider（CEPC） is a future Higgs factory proposed by the Chinese high energy physics community. It will operate at a center-of-mass energy of 240–250 Ge V. The CEPC will accumulate an integrated luminosity of 5 ab-1over ten years of operation, producing one million Higgs bosons via the Higgsstrahlung and vector boson fusion processes. This sample allows a percent or even sub-percent level determination of the Higgs boson couplings. With GEANT4-based full simulation and a dedicated fast simulation tool, we have evaluated the statistical precisions of the Higgstrahlung cross section σZH and the Higgs mass m H measurement at the CEPC in the Z →μ~＋μ^-channel. The statistical precision of σZH（m_H） measurement could reach 0.97%（6.9 MeV） in the model-independent analysis which uses only the information from Z boson decays. For the standard model Higgs boson, the m H precision could be improved to 5.4 Me V by including the information from Higgs decays. The impact of the TPC size on these measurements is investigated. In addition, we studied the prospect of measuring the Higgs boson decaying into invisible final states at the CEPC. With the Standard Model ZH production rate, the upper limit of B（H → inv.） could reach 1.2% at 95% confidence level.

Physics design of collimators to reduce lost particle background at the CEPC

At the CEPC （Circular Electron Positron Collider）, which is proposed by the Chinese high energy physics community, the dominant background comes from radiative Bhabha scattering and the beamstrahlung effect according to preliminary research. Therefore, it is necessary to incorporate a collimator system to intercept particles that may be lost near the interaction region （IR）. In this paper, we introduce some limitations in choosing the position and width of the collimators. A certain parameter range is determined which is confined by the β function and the width of the collimators. A suitable choice of the half width is made by exploring this parameter range. A simulation of the particle loss rate in the IR and the hit density in the vertex detector with and without the collimators shows that the set of parameters of the collimators we designed is appropriate and effective.

基于DIRAC的高能物理分布式计算系统在CEPC实验上的应用

2 0 1 2年L H C实验发现希格斯粒子后,我国粒子物理学界规划了高能环形正负电子对撞机(CEPC),以及它升级后的超级质子对撞机(Spp C),用于研究希格斯物理,并在高能量前沿探索超越标准模型的新物理。CEPC实验的计算量非常大,即使是在预研阶段,一次探测器全模拟就需要833万CPU小时的计算量和1PB存储空间。当本地计算资源不足时,分布式计算是一种快速整合合作单位计算资源来满足实验大量计算需求的有效方法。2012年,高能所基于DIRAC中间件建立了一套约2000 CPU核规模的分布式计算系统,服务于BESIII实验。本文介绍了将此分布式计算系统扩展到支持CEPC实验的改进方案,并介绍了此系统在CEPC实验的实际应用。

基于JavaFx的硅像素顶点探测器原型机数据获取软件的研制

在环形正负电子对撞机(CEPC)实验中,硅像素顶点探测器对空间位置分辨率有着极高的要求,这使得其芯片和探测器设计面临巨大挑战。太初系列硅像素探测器芯片(TaichuPix)是基于CMOS技术的一种重要尝试,其首款工程批芯片被应用于开发第一个全尺寸顶点探测器原型机。为满足顶点探测器原型机在实验中的特定需求,设计并实现了一套基于JavaFx框架的跨平台数据获取系统。该系统能够高效地进行探测器原型机的配置、数据采集、在线数据校验和实时监测,同时提供了一个用户友好的图形化界面。在实验室环境及德国电子同步加速器研究所(DESY)的束流实验中,数据获取系统的功能完善性和运行稳定性得到了验证,充分满足了硅像素顶点探测器原型机的实验需求。

Mixed electroweak-QCD corrections to e^+e^-→μ^+μ^-H at CEPC with finite-width effect

The associated production of Higgs boson with a muon pair, e^+e^-→μ+μ-H, is one of the golden channels to pin down the properties of the Higgs boson in the prospective Higgs factories exemplified by CEPC.The projected accuracy of the corresponding cross section measurement is about per cent level at CEPC. In this work, we investigate both O(α) weak correction and the O(ααs) mixed electroweak-QCD corrections for this channel,appropriately taking into account the effect of finite Z^0 width. The μ^+μ^-invariant mass spectrum is also predicted.The mixed electroweak-QCD correction turns out to reach 1.5% of the Born-order result, and thereby must be included in future confrontation with the data. We also observe that, after including higher-order corrections, the simplified prediction for the integrated cross section employing the narrow-width-approximation may deviate from our full result by a few per cents.

Study of beamstrahlung effects at CEPC

The discovery of a 125 GeV Higgs boson at the LHC marked a breakthrough in particle physics. The relative lightness of the new particle has inspired consideration of a high-luminosity Circular Electron positron Collider （CEPC） as a Higgs Factory to study the particle＇s properties in an extremely clean environment. Given the high luminosity and high energy of the CEPC, beamstrahlung is one of the most important sources of beam- induced background that might degrade the detector performance. It can introduce even more background to the detector through the consequent electron-positron pair production and hadronic event generation. In this paper, beamstrahlung-induced backgrounds are estimated with both analytical methods and Monte Carlo simulation. Hit density due to detector backgrounds at the first vertex detector layer is found to be -0.2 hits/cm2 per bunch crossing, resulting in a low detector occupancy below 0.5%. Non-ionizing energy loss （NIEL） and total ionizing dose （TID）, representing the radiation damage effects, are estimated to be -1011 1 MeV neq/cm2/yr and --300 kRad/yr, respectively.

Measurements of decay branching fractions of H→b■/c■/gg in associated (e^+e^-/μ^+μ^-)H production at the CEPC

The high-precision measurement of Higgs boson properties is one of the primary goals of the Circular Electron Positron Collider(CEPC).The measurements ofH→bb/cc/gg decay branching fraction in the CEPC experiment is presented,considering a scenario of analysing 5000 fb-1 e^+e^-collision data with the center-of-mass energy of 250 Ge V.In this study the Higgs bosons are produced in association with a pair of leptons,dominantly mediated by the ZH production process.The statistical uncertainty of the signal cross section is estimated to be about 1%in theH→bb final state,and approximately 5%-10%in theH→cc/gg final states.In addition,the main sources of the systematic uncertainties and their impacts to the measurements of branching fractions are discussed.This study demonstrates the potential of precise measurement of the hadronic final states of the Higgs boson decay at the CEPC,and will provide key information to understand the Yukawa couplings between the Higgs boson and quarks,which are predicted to be the origin of quarks’masses in the standard model.