Developing cold-resistant high-adhesive electronic substrate for WIMPs detectors at CDEX

Herein we report a prototypical electronic substrate specifically designed to serve the weakly interacting massive particles(WIMPs)detectors at the China Dark Matter Experiment(CDEX).Because the bulky high-purity germanium(HPGe)detectors operate under liquid-nitrogen temperatures and ultralow radiation backgrounds,the desired electronic substrates must maintain high adhesivity across different layers in such cold environment and be free from any radioactive nuclides.To conquer these challenges,for the first time,we employed polytetrafluoroethylene((C2F4)n)foil as the base substrate,in conjunction with ion implantation and deposition techniques using an independently developed device at Beijing Normal University for surface modification prior to electroplating.The remarkable peeling strengths of 0.88±0.06 N/mm for as-prepared sample and 0.75±0.05 N/mm for that after 2.5-days of soaking inside the liquid nitrogen were observed,while the regular standards commonly require 0.4 N/mm^0.6 N/mm for electronic substrates.

技巧三则 轻松玩转CDex软件

CDex 软件能轻松地将 CD 抓取为WAV、MP3、WMA、OGG、AAC、APE、VQF、MP+等流行的音频文件,并能实现各种格式之间的相互转换。它与 CDDB 无缝结合,可以轻松获取 CD 信息,最令人不可思议的,它竟然是免费软件。cDex 操作非常简单,功能却超级强大,在这里介绍三绝活,让你轻松玩转 CDex。

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Probing dark matter particles from evaporating primordial black holes via electron scattering in the CDEX-10 experiment

Dark matter(DM)is a major constituent of the Universe.However,no definite evidence of DM particles(denoted as“χ”)has been found in DM direct detection(DD)experiments to date.There is a novel concept of detectingχfrom evaporating primordial black holes(PBHs).We search forχemitted from PBHs by investigating their interaction with target electrons.The examined PBH masses range from 1×10^(15)to 7×10^(16)g under the current limits of PBH abundance fPBH.Using 205.4 kg·day data obtained from the CDEX-10 experiment conducted in the China Jinping Underground Laboratory,we exclude theχ-electron(χ-e)elastic-scattering cross sectionσ_(χe)~5×10^(-29)cm^(2)forχwith a mass■keV from our results.With the higher radiation background but lower energy threshold(160 eV),CDEX-10 fills a part of the gap in the previous work.If(m_(χ),σ_(χe))can be determined in the future,DD experiments are expected to impose strong constraints on fPBHfor large MPBHs.

Searching for^(76)Ge neutrinoless double beta decay with the CDEX-1B experiment

We operated a p-type point contact high purity germanium(PPCGe)detector(CDEX-1B,1.008 kg)in the China Jinping Underground Laboratory(CJPL)for 500.3 days to search for neutrinoless double beta(0νββ)decay of^(76)Ge.A total of 504.3 kg⋅day effective exposure data was accumulated.The anti-coincidence and the multi/single-site event(MSE/SSE)discrimination methods were used to suppress the background in the energy region of interest(ROI,1989–2089 keV for this work)with a factor of 23.A background level of 0.33 counts/(keV⋅kg⋅yr)was realized.The lower limit on the half life of^(76)Ge 0νββdecay was constrained as T_(1/2)^(0ν)>1.0×10^(23)yr(90%C.L.),corresponding to the upper limits on the effective Majorana neutrino mass:<mββ><3.2–7.5 eV.

First results on ^(76)Ge neutrinoless double beta decay from CDEX-1 experiment

We report the first results on 76Ge neutrinoless double beta decay from stage one of the China dark-matter experiment （CDEX）. A p-type point-contact high-purity germanium detector with a mass of 994g has been installed to detect neutrinoless double beta decay events, as well as to directly detect dark matter particles. An exposure of 304kgd has been analyzed over a wide spectral band from 500keV to 3MeV. The average event rate obtained was about 0.012 counts per keV per kg per day over the 2.039MeV energy range. The half-life of76Ge neutrinoless double beta decay derived based on this result is 70v2〉6.4× 1022 yr （90%C.L.）. An upper limit on the effective Majorana-neutrino mass of 5.0eV has been achieved.

Introduction to the CDEX experiment

It is believed that weakly interacting massive particles （WIMPs） are candidates for dark matter （DM） in our universe which come from outer space and might interact with the standard model （SM） matter of our detectors on the earth. Many collaborations in the world are carrying out various experiments to directly detect DM particles. China Jinping underground Laboratory （CJPL） is the deepest underground laboratory in the world and provides a very promising environment for DM search. China Dark matter EXperiment （CDEX） is going to directly detect the WIMP flux with high sensitivity in the low WIMP-mass region. Both CJPL and CDEX have achieved a remarkable progress in recent three years. CDEX employs a point-contact germanium （PCGe） semi-conductor detector whose energy threshold is less than 300 eV. In this report we present the measurement results of muon flux, monitoring of radioactivity and radon concentration carried out in CJPL, as well describing the structure and performance of the 1 kg-PCGe detector in CDEX-1 and 10 kg- PCGe detector array in CDEX-10 including the detectors, electronics, shielding and cooling systems. Finally we discuss the physics goals of CDEX-1, CDEX-10 and the future CDEX-1T experiments.

中国暗物质实验(CDEX)合作组研究进展

暗物质是当今物理学最基本也是最吸引人的前沿研究课题之一,对认识宇宙起源、演变和结构以及物质的本源等基本科学问题具有十分重要的意义.暗物质的理论研究和实验探测经过几十年的积累和发展已经取得了长远的进步.实验上有多种方法可以进行暗物质粒子的探测,直接探测是一种非常重要的手段.本文评述了暗物质直接探测方法的原理和当今国际国内采用直接探测法的不同实验的研究现状,着重介绍了中国暗物质实验(China Dark matter Experiment,CDEX)合作组的研究历程、探测技术和数据分析方法、以及研究取得的重要成果和未来规划.

First experimental constraints on WIMP couplings in the effective field theory framework from CDEX

We present weakly interacting massive particles(WIMPs) search results performed using two approaches of effective field theory from the China Dark Matter Experiment(CDEX), based on the data from both CDEX-1B and CDEX-10 stages. In the nonrelativistic effective field theory approach, both time-integrated and annual modulation analyses were used to set new limits for the coupling of WIMP-nucleon effective operators at 90% confidence level(C.L.) and improve over the current bounds in the low mχregion. In the chiral effective field theory approach, data from CDEX-10 were used to set an upper limit on WIMP-pion coupling at 90% C.L. We for the first time extended the limit to the m_(χ)<6 GeV/c^(2) region.

CDEX-1 1 kg point-contact germanium detector for low mass dark matter searches

The CDEX collaboration has been established for direct detection of light dark matter particles, using ultra-low energy threshold point-contact p-type germanium detectors, in China JinPing underground Laboratory （CJPL）. The first 1 kg point-contact germanium detector with a sub-keV energy threshold has been tested in a passive shielding system located in CJPL. The outputs from both the point-contact P＋ electrode and the outside N＋ electrode make it possible to scan the lower energy range of less than 1 keV and at the same time to detect the higher energy range up to 3 MeV. The outputs from both P＋ and N＋ electrode may also provide a more powerful method for signal discrimination for dark matter experiment. Some key parameters, including energy resolution, dead time, decay times of internal X-rays, and system stability, have been tested and measured. The results show that the 1 kg point-contact germanium detector, together with its shielding system and electronics, can run smoothly with good performances. This detector system will be deployed for dark matter search experiments.

Study of the material photon and electron background and the liquid argon detector veto efficiency of the CDEX-10 experiment

The China Dark Matter Experiment （CDEX） is located at the China Jinping Underground Laboratory （CJPL） and aims to directly detect the weakly interacting massive particles （WIMP） flux with high sensitivity in the low mass region. Here we present a study of tile predicted photon and electron backgrounds including the background contribution of the structure materials of the germanium detector, the passive shielding materials, and the intrinsic radioactivity of the liquid argon that serves as an anti-Compton active shielding detector. A detailed geometry is modeled and the background contribution has been simulated based on the measured radioactivities of all possible components within tile GEANT4 program. Then the photon and electron background level in the energy region of interest （〈10-2events-kg1·day 1·keV-1 （cpkkd）） is predicted based on Monte Carlo simulations. The simulated result is consistent with the design goal of the CDEX-10 experiment, 0.1cpkkd, which shows that the active and passive shield design of CDEX-10 is effective and feasible.

中国锦屏地下实验室与稀有物理实验

中国锦屏地下实验室是目前世界上岩石覆盖最深的深地实验室,对宇宙线μ子具有良好的屏蔽作用,具有极低的宇宙线通量,因此适用于开展对稀有物理事例的探测实验。目前,包括中国暗物质实验(China Dark matter EXperiment,CDEX)、粒子和天体物理氙实验(Particle and Astrophysical Xenon Experiments,PandaX)、锦屏深地核天体物理实验装置(Jinping Underground Nuclear Astrophysics Experiment,JUNA)等实验组已经入驻锦屏实验室,对暗物质直接探测、无中微子双β衰变、天体核反应等一系列稀有物理事例进行实验探测,并给出了一系列国际先进水平的研究成果。本文总结了中国锦屏地下实验室自成立以来的发展过程和本底控制情况,并对实验室中各个实验组所开展实验的物理意义、实验原理、关键技术、物理成果等进行介绍,同时给出实验组接下来的实验计划。

基于ZYNQ的千兆以太网接口读出模块ZYNQBee的研制及应用

ZYNQ是集成了现场可编程阵列(Field-Programmable Gate Array,FPGA)和高性能双核ARM Cortex-A9处理器的全新架构的SoC(System On Chip)。核电子学领域的数据读出方式,从传统的"处理器+FPGA"的双芯片解决方案到目前的ZYNQ单芯片解决方案,不仅有效地减小读出电子学硬件的尺寸和功耗,而且极大地提高FPGA和处理器之间的有效带宽,为整个读出电子学带来了新的发展。介绍了基于ZYNQ XC7Z010单芯片读出模块的研制细节,包括新架构和传统架构的对比,新架构硬件设计细节、难点及性能,其中涉及DDR3(Double Data Rate 3)SDRAM(Synchronous Dynamic Random Access Memory)布线的关键问题、千兆以太网接口以及嵌入式Linux的移植等。最后,介绍ZYNQBee在中国暗物质实验(China Dark matter EXperiment,CDEX)高纯锗探测器数据采集板卡上的应用,测试表明:以太网口的数据读出平均带宽超过了700 Mb·s-1。

简便快捷CD音轨转MP3

MP3播放器越来越普及了,很多DVD播放机也可以直接播放MP3的光碟,如果我们将自己的一大堆的音乐CD转为MP3文件,就可以随时下载到MP3播放器中。也可以刻录为MP3的光碟——一张光碟差不多可以装下10多张CD的歌曲,这样用可以用DVD播放机播放MP3,一天都不用换CD盘了。这里介绍一个小巧但使用简便快捷的抓取CD音轨并转为MP3的软件——CDex,这是一个完全免费的软件。

把更多的音乐装入MP3

一般情况下，MP3 Player只持支持WMA和MP3（虽然可能也支持WAV，但它体积太大，相信没有谁会放WAV到MP3 Player中），但是我们从网上还可能会下载到其他格式的音乐文件。如果想把它装入MP3播放器中收听的话，这时就必须进行转换。很多的转换工具需要收费，同时还无法控制其编码率，这样就会使得转换出的文件较大。现在只要下载并安装CDex软件，利用它就可以批量转音乐文件，还能够自由地控制其编码率，从而可以控制文件大小，将更多的音乐装入MP3播放器。

地下实验室基坑混凝土工艺浅析——中国锦屏地下实验室二期扩建工程

中国锦屏地下实验室是为探测宇宙暗物质而建国家重点实验室,为保证实验室洁净和安全,CDEX实验室、PANDEX实验室内探测器基坑需要做钢筋混凝土衬砌,包括探测器基坑侧壁混凝土和基础底板混凝土,本文对钢筋混凝土浇灌、钢筋绑扎、脚手架搭建、模板工程进行了详细介绍。

暗物质探测实验液氩反符合探测器杂质影响分析

CDEX装置采用液氩反符合屏蔽方法降低本底,液氩中的杂质可能会对反符合效率造成影响。CDEX装置反符合效率与高纯锗晶体总探测效率、液氩探测器总探测效率有关。6个因素会影响液氩探测器总探测效率。液氩中的杂质会改变慢成分衰减时间。杂质通过焠灭和吸收作用,降低闪烁光产额和吸收闪烁光子,进而降低反符合探测效率。以氮和氧为例,计算了不同含量时发生的焠灭作用对于反符合效率的影响。结果表明,仅考虑焠灭作用条件下,为了使反符合效率达到90%以上,需要将液氩介质中的氮和氧含量降低到约100 ppb量级。

液氩探测系统的设计与信号分析

中国暗物质实验组将对暗物质(弱相互作用粒子)进行直接探测,其中CDEX-10的项目中将利用低阈值高纯锗作为主探测器,液氩作为反符合系统并且为高纯锗提供低温环境。液氩探测系统的性能研究和信号分析,是液氩反符合系统的关键技术。该项目通过搭建小型的液氩信号采集实验装置、建立数据采集和数据分析系统,完成了整个系统的调试和液氩中宇宙线的信号分析;得到了液氩中信号的波形特性以及甄别因子;为暗物质中液氩纯度的研究和TPB镀膜的研究奠定了基础。