1. 用于空间暗物质探测的数字量能器研究 孙希磊 中国科学院 “ 核探测技术与核电子学 ” 重点实验室 中国科学院高能物理研究所 第十五届全国核电子学与核探测技术学术年会

2. 报告内容 1. 暗物质探测简介 2. 探测器设计 3.MC 模拟研究 4. 探测器原型研究 5. 总结 2

3. 暗物质及其证据 旋转星系曲线 弱引力透镜 强引力透镜 3 暗物质是什么？？？？

4. 粒子物理中的暗物质候选者 热门候选者 ▫ Stable weakly interacting massive particles (WIMPs) of mass 10GeV – 10TeV (preferred by most of theorist) ▫ Massive neutrinos ▫ Axions ▫ Kaluza Klein particles WIMPs occur in several well-motivated theories beyond the Standard Model such as ▫ Supersymmetry ▫ Inert Higgs models etc. 4 我们的探测目标是 WIMPs

5. WIMP 的探测机制 直接探测 : 探测暗物质与核的碰撞信号 到现在，没有确证的信号，只给出了质量截面排除线 间接探测 : 探测暗物质湮灭信号 SM -> 5

6. 暗物质的判定性证据 M χ =1.5TeV 湮灭线峰 diffuse radiation Example for gamma-ray spectrum of DM annihilation Line signature from DM annihilation to double gamma-ray is the decisive evidence of DM 6

7. 宇宙线流强 Range 30GeV—10TeV Flux of electrons: ~ 10 -2 —10 -3 of protons Flux of gamma-rays: ~ 10 -3 —10 -6 of protons To identify electrons and gamma-rays, excellent capability of proton rejection with power ~10 5 is necessary 7

8. 中国空间站 A payload for dark matter search is proposed by IHEP the detector should has capabilities : Energy range 30GeV-5TeV (cover WIMP mass range) Energy resolution <5%(detect line signature requirement ) Background rejection power > 10 5 (suppress proton background requirement) Total power <500 Watts Total mass <1.5 Tons 2020 Space Station will be built 8

9. 探测器概念设计 The detector has two chief components: Anti-Coincidence Detector(ACD) ACD is a positional sensitive plastic scintillator detector in order to reject charged particles for the gamma-rays observation. Digital Imaging Calorimeter(DIC) DIC is a 3D Crystal array, each crystal is a little cube with one face coupled with WLS fiber which collect and guild photons to ICCD camera. All separate cubes are glued together. “Digital” means: for each crystal Hit mark “1” Non-Hit mark “0” All the “01” describe the shower image. We can get the information of particle energy, particle type and incident angle by image analysis. 9

10. ACD 结构 80cm 1cm ACD is composed of 1x1x80cm plastic scintillator array along x and y direction which covers more than 5/6 of the main body. Each scintillator has a WLSF inbuilt in a groove on surface. Read out devoice is SiPM. ACD is positional sensitive so the incident position of charged particle can be got associated with the shower axis in DIC. backflash 10

11. 触发结构 WLSF PMT One fiber attach the surfaces of a string of crystals All fibers coupled with one PMT when a high energy particle incident, we can get a fast signal(<100ns) which direct proportion the particle energy. So a threshold can be set for trigger. Trigger PMT Discriminator Trigger signal DIC Image intensifier ICCD camera computer sum Schematic view of the system ADCACD SiMT 11

12. 探测器的主要特点 Digital imaging so has no amplitude saturation problem 5 sensitive faces so has a large field of view High level of granularity so has Good particle identify power and Good angle resolution CCD read out with low power ~10w ACD is positional sensitive to suppress backflash charged particle Fermi detector CALET detector 12

13. 探测器性能 MC 模拟研究 Energy relationship Energy resolution Angular resolution Gamma/proton separation 13

14. 探测器几何结构 Point source gamma Total length is 60cm,~32r.l. Little crystal cube side length is 1.5— 4.5 cm There is a 1mm glue interval between two crystals Code: Geant4 Physics list: QGSP Particle vertical incident Digital energy cut is 12MeV for each crystal CsI 1mm glue interval 14

15. Energy relationship High energy range linear relationship is good low energy range linear relationship is a little worse From the MC data we found the relationship is: 15

16. 能量分辨率 ~4% can be reached above 500GeV Energy distribution 1000GeV gamma-ray resolution 3.27% Energy resolution compare of different granularity 1.5—4.5 cm 16

17. 角度分辨率 angular resolution compare of different granularity 1.5—4.5cm Reconstruction of shower axis position distribution of incident particle angular distribution of incident particle ~0.5 o can be reached over 500GeV 17

18. 粒子鉴别 (PID) Two main differences : 1.Proton induced showers are longitudinally wider than electron showers due to the spread of secondary particles in nuclear interactions. 2.An electron induced shower will start and die off earlier than a proton shower Gamma-ray shower image Proton shower image 3D gamma-ray shower2D gamma-ray shower 3D proton shower 2D proton shower 18

19. Gamma/proton 分辨 The input is Signal: gamma-ray 100GeV 140000 events Background: proton 100GeV—5000GeV power law 2.7 1M events proton rejection power ~5x10⁵ Signal efficiency 95% CsI2.5x24 TMVA output of gamma/proton separation Background rejection versus signal efficiency BDT has a better performance 19

20. Gamma/electron 分辨 The input is Signal: gamma-ray 100GeV 140000 events Background: electron 100GeV 160000 events electron rejection power ~1x10⁴ Signal efficiency 45% CsI2.5x24 Difference: Electron shower start earlier than gamma-ray shower TMVA output of gamma/electron separation Background rejection versus signal efficiency 20

21. 实验研究 单元结构 2x2x6 阵列 宇宙线测试 容量分析 21

22. 单元结构 Crystal side length: 2.5cm WLS fiber diameter: Φ300um Crystal packing ESR WLS fiber plate Crystal with WLSF 22

23. 单元宇宙线测试 CsI(Na) has better performance muon Trigger PMT WLSF 1.5m PMT xp2020 CsI(Na) Differern crystal compare muon MIP spectrum View of the system 23

24. 2x2x6 阵列 Trigger PMT FOT Image intensifier ICCD 2x2x6 array Φ300um 1.5m long WLSF 24

25. 宇宙线测试系统 muon Trigger PMT WLSF 1.5m Fiber optic taper Image intensifier lensICCD CsI(Na) Trigger PMT1 Trigger PMT2 Discriminator and Trigger signal CsI(Na) photon Image intensifier ICCD camera computer 25

26. 宇宙线测试结果 MIP (12MeV) signal Position calibration muon event 4 fibers with 100um interval in each layer Signal is clear And the system works well 26

27. 容量分析 Magnification of FOT and size of CCD are the key factors for capacity. For φ300um fiber with 100um interval and 450000 pixels CCD Magnification capacity 2:1 ~4500 fibers 5:1 ~28000 fibers 28000 can cover a 30x30x30 array Only one CCD system needed for the whole calorimeter. Fiber optic taper(FOT) 27

28. 总结 A scheme of 60cm cube CsI(Na) array is proposed: 5faces sensitive,digital image,32r.l. ~1T, 30GeV—5TeV The preliminary simulation is done. gamma/proton separation ~5x10 5 (95% eff. DIC only) electron/proton separation ~1x10 4 (45% eff. DIC only) Energy resolution ~4% Angular resolution ~0.5 o The prototype has been built and test. 28

29. Backup 29

30. Particle identification with TMVA 30

31. PID variables Number of Hits in each layer Hits of each layer Response of TMVA for variable 31

32. CsI(Na) intrinsic light yield Fe55 5.9KeV Light yield: 3.2p.e./KeV @2us integration time (no ESR packaging) 32

33. Light yield compare ESR packing: Peak at 769 resolution 3.51% Naked: Peak at 330 resolution 5.88% ESR packing is 2.33 times larger than naked ESR packing light yield: 7.4 p.e./KeV @2us integration time Integration time: 20us CsI(Na) 1.625 times larger than NaI(Tl) Light yield: 12 p.e./KeV 33

34. Image Intensifier photon– electron—intensified photons It’s key effective is: Intensified image Photon delay (delay line for photon) ~1ms so we have enough time for trigger Photo cathode Q.E. : Present Second generation ~15% @500nm future Third generation ~50% @500nm 34

35. ICCD system overview Gating: a crucial feature of high speed ICCD cameras trigger No trigger shutter is open shutter is closed If the voltage U C between photocathode and multichannel plate is negative, the photoelectrons are accelarated towards the multi channel plate. This means that the shutter is open. If the voltage U C is positive, the photoelectrons are kept at the photoathode, thus the shutter is closed 35

36. 2.5x24 4.0x15 2.5x32 3.0x20 36

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38. CHINA 30-5000 18000 10 0.5(500GeV) 4 (500GeV) 2x10 -9 38

39. Sr90 spectrum 2MeV~25p.e. Fiber interval 1.2cm 39

40. ACD structure ACD is composed of a 80x80x1cm plastic scintillator with WLSF array along x and y direction inbuilt in grooves on two surface. which covers more than 5/6 of the main body. Read out devoice is SiPM or Multi- Anode PMT. 80cm 1cm Charged particle incident position can be get associated with the shower axis in DIC. the hit position can be get through Centroid method. 40

41. unit structure Crystal: CsI(Na) Wave length: 420nm Decay time: short 550ns long 4us Radiation length: 1.85 cm Density: 4.51 g/cm 3 Hygroscopic : weak Wave length shift fiber(WLSF) BCF-91A BICRON shift blue to green Emission peak: 494nm Decay time: 12ns ESR reflect packing reflectivity >99% 2.5cm 41

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43. 高能物理学会 2010 年会 43 可探测性研究 在典型的条件下（ 3m 2 sr 探测器，空间站轨 道巡天运行 1 年， 2% 能量分辨率）可探测的 暗物质湮灭线最小流量与暗物质粒子质量 的关系

44. 高能物理学会 2010 年会 44 可探测性研究：巡天观测 最小灵敏流量与探测器 能量分辨率、质子排斥、 电子排斥性能的关系 能量分辨率的影响最大

45. 高能物理学会 2010 年会 45 可探测性研究：针对银心