江门中微子实验的探测器模拟

1. 江门中微子实验的探测器模拟 高能所 邓子艳 2014年4月21日 湖北 武汉 中国物理学会高能物理分会第九届全国会员代表大会暨学术年会

2. 江门中微子实验（JUNO） 顶部探测器 中心探测器 水切伦科夫探测器

3. JUNO离线软件系统 • 模拟软件： • 基于Geant4的探测器模拟 • 读出电子学模拟 • 本底混合 DetSim ElecSim TriggerSim ReadoutSim

4. 探测器模拟软件 • 在探测器设计阶段，探测器模拟软件的必要性 • 针对不同探测器设计方案的模拟，为探测器设计提供参考依据 • 能量分辨率 • 本底事例率 • 模拟软件可用于顶点和能量重建算法的研究 • 模拟软件用于刻度研究 • 一方面，要保证模拟软件的可用性 • 为探测器设计服务 • 及时给出模拟结果 • 另一方面，在整个离线软件框架下，软件功能的逐步完善 • 实现完整的模拟流程 • 产生子->探测器模拟->电子学模拟->触发模拟->读出系统模拟 • 统一的几何管理 • 良好的用户接口 • 速度和性能的优化

5. Generator && Interfaces • Generator • Inverse beta decay • Written in C++, imported from Dayabay • Radioactivity • Uranium(238U), Thorium(232Th), Potassium(40K) • AP generator，Written in Fortran by Andreas Piepke • GenDecay (in C++) • Generator interfaces • Support to generate: • Particles with specified name and momentum • At fixed position (x0,y0,z0) • Randomly on a surface R=R0 • Randomly inside a spherical volume R<R0,R1<R<R2 • Randomly in specified material, for example, PMT glass

6. GenDecay 1.数据来源：Evaluated Nuclear Structure Data File (ENSDF) Data Sets （记录各种原子核的可能衰变，及其分支比） 2.通过ENSDF的数据来构建衰变链 （ENSDF的数据需要使用libmore来转换） NucState: 描述原子核的类，存储了Z/A，半衰期，能级，以及可能发生的衰变（NucDecay） NucDecay: 描述一个衰变，存储了指向母核和子核的指针(NucState*),衰变类型（α,β,γ），衰变释放的能量，以及分支比

7. An example：U-238 to Th-234 U-238 level=0 keV[0] A DECAY E=4.038 MeV br=0.0780172% Th-234 level=163 keV[0] Gamma E=0.1135 MeV br=100% A DECAY E=4.151 MeV br=20.9046% Th-234 level=49.55 keV[0] Gamma E=0.04955 MeV br=100% A DECAY E=4.198 MeV br=79.0174% Th-234 level=0 keV[0]

8. Optical parameters && Geometry • Optical parameters • Based on DYB (tuned to data), except QE and absorption length • maxQE • from 25% -> 35% • LS absorption length • From 25m -> 40m • LS attenuation length • from 15m = absorption 25m + Rayleigh scattering 40m • to 20 m = absorption 40m + Rayleigh scattering 40m • Geometry • 20k ton liquid scintillator • Buffer thickness in front of PMT is 0.8m Acrylic tank：F35.4m Stainless Steel tank ：F38.4m F=0.8m, G=0.7m A=17.7m, B=1.05m, C=0.45m A+B=18.75m (position of PMT sphere center) B+C=1.5m, Radius of PMT: 0.254m

9. Detector design options DetSim1 有机玻璃罐方案 LS/sphericalacrylic vessel/water/ steel truss DetSim2: 模块方案 LS/acrylic module/steel tank DetSim3: 气球方案 LS/balloon/steel tank buffer: mineral oil Triangle module or single PMT module LAB inside modules, With LS in the gap between modules

10. Geometry DetSim1 && DetSim3 && DetSim2(single PMT module) DetSim2 (Triangle Module) PMT sphere center: @18.75m Total: 17520 PMTs Coverage: ~77% PMT sphere center: @18.75m Total: 16720 PMTs Coverage: ~76.7% 。

11. Compare between different detector options • (1)Radioactivity background event rate • From PMT glass • From LS • From Acrylic • From balloon • From dust on balloon • From steel

12. 14 radioactive decays in the chain 10 radioactive decays in the chain

13. Generator BG event rate from PMT glass (estimated with Schott glass) Mass of glass per PMT = 10kg 238U && 232Thgenerator: Written in Fortran, by Andreas Piepke If estimate with Schott glass, the generator event rate is ~1MHz If estimate with DYB PMT glass, the generator event rate is ~8MHz

14. 模块方案 vs 气球方案 vs 有机玻璃罐方案 F=80cm 238U background from PMT glass

15. 本底事例率随屏蔽层厚度的变化 (~0.5MeV) F=30/60/80cm (238U+232Th+40K Background from PMT glass)

16. Background from acrylic

17. Background from stainless steel

18. Background from dust/balloon/LS Background from dust on balloon surface Background from balloon

19. Summary of single rates (0.8m buffer) • 对有机玻璃罐方案和气球方案，增加屏蔽层厚度可有效减小single rates • DetSim1(Schott glass): 1.1m(30Hz), 1.4m(1Hz) • DetSim3(Schott glass): 1.1m(100Hz), 1.4m(20Hz) • 而对模块方案则不然

20. Compare between different detector options (2)Energy resolution

21. Non-uniformity • 1MeV gamma generated at R<17.7m, energy not deposited totally at R>17m • 有机玻璃罐方案: optical photons total reflected at large R because of large difference of the refraction index between water and acrylic Refraction index Non-uniformity R=15.7m R=17m

22. 有机玻璃罐方案的能量重建 • Strategy I: total charge corrected with calibration curve

23. 有机玻璃罐方案的能量重建 • Strategy II: charge likelihood, consider the contribution of total reflection in the reconstruction

24. 有机玻璃罐方案的能量重建 • Strategy III: charge likelihood, doesn’t consider the total reflection at first, and then correct the non-uniformity through calibration

25. 气球方案的能量分辨率 • LS+Oil: using IBD events, applying 17m vertex cut, and correcting the non-linearity Charge Likelihood shows better performance than total PE

26. 有机玻璃罐方案的能量分辨率 • LS+Water: Total Charge/Charge Likelihood (Strategy III)

27. 有机玻璃罐方案 vs 气球方案 For total charge, there is little difference in energy resolution for LS+water and LS+Oil • Total Charge: comparison between LS+Oil and LS+Water

28. 有机玻璃罐方案 vs 气球方案 For charge likelihood method, the performance of LS+Oil is slightly better than LS+Water • Charge Likelihood: comparison between LS+Oil and LS+Water (with 17m cut)

29. Background Mixing • Generate U/Th/K events randomly in PMT glass • Generate gamma/IBD events in LS • Mixing without electronics simulation • Using the generator event rate to sample the number of background events in one time window (for example: 300ns) • Sum the total p.e. of signal and background • Mixing during electronics simulation • Sample the BK event start time in one time window • Mix the hits from signal and background for each PMT • Pulse integration for each PMT

30. Mixing BG at different generator levels , without electronics simulation Detector type: DetSim2 Single PMT module, 30cm LAB E_true vs E_rec for e+ from IBD

31. Mixing BG at different generator levels , without electronics simulation Detector type: DetSim2 Single PMT module + balloon, 30cm LAB E_true vs E_rec for e+ from IBD

32. Mixing BG at different generator levels , without electronics simulation Detector type: DetSim2 Single PMT module + balloon, 80cm LAB E_true vs E_rec for e+ from IBD

33. Background mixing during ElecSim • A simple NHit trigger is implemented in ElecSim • Signal and background(from U/Th/K) are accidental coincidence in one readout window Single gamma energy spectrum after BG mixing DetSim2: single PMT module + balloon, 30cmLAB, mix 10 MHz BG

34. 现阶段探测器设计方案 经过3月份的中心探测器方案评审之后，排除了本底事例率高的模块方案，现阶段中心探测器的首选方案是有机玻璃罐方案，备选方案是气球方案。

35. New PMT个数18306个 覆盖率77.65% PMT前端屏蔽层厚度： 1.4~1.5m Acrylic tank：F35.4m Stainless Steel tank ：F39.9m A=17.7m (LS) B=(0.12+1.426+0.254)m=1.8m C=0.45m A+B=19.5m (PMT place) A+B+C=19.95m

36. 光学参数 吸收长度 发射谱 瑞利散射长度 吸收重发射几率 量子效率 折射率 光产额：10400/MeV 液闪的瑞利散射长度 30 m @430nm 液闪的衰减长度 20 m @430 nm 液闪的吸收长度为 60 m @430 nm

37. PMT保护罩 PMT防爆罩形状与PMT形相同， 厚度为9mm，与PMT有1mm的空隙，空隙内填充水。 有机玻璃罐方案 气球方案 加或不加PMT保护罩的TotalPE分布

38. Muon simulation • 高能muon穿过大体积的液闪探测器，光学模拟过程速度非常慢，内存占用量大 • 可以通过对muon事例的光产额进行scale，达到提高模拟速度的目的 • 对muon事例设计新的数据结构，减小内存占用量 Generate Mu- at (0, 0, 20m) Momentum = (0, 0, -P)

39. Data Structure for muon events Only save firstHitTime and nPE (Merge the hits in a time window) Memory Usage: < 1GB

40. Summary • A simulation tool for preliminary study of detector design, calibration, and reconstruction has been developed for JUNO • Performance of different detector design options have been compared • DetSim algorithm has been integrated into JUNO offline framework • Detailed detector simulation for two options is still on-going

41. THANKS

42. 模块方案，来自PMT玻璃的天然放射性本底事例率模块方案，来自PMT玻璃的天然放射性本底事例率 屏蔽层厚度 F=30cm/60cm/80cm 238U+232Th+40K

43. Triangle Modules 5/21 PMT 5/26 PMT 5/17 PMT 5/21 PMT

44. Triangle Modules 0/28 PMT 5/26 PMT 5/21 PMT 5/26 PMT

45. Triangle Modules 5/26 PMT 9/26 PMT The PMTs marked with red numbers are in down layer, the other PMTs in up layer. Triangle side length is about (3-4)m. The buffer layer (LAB) in front of PMT in module is 80cm , the module length is about 1.919m. Compared with single PMT module: Less LS between modules. Longer module length because two layers of PMT in modules.

46. Event rate (Schott Glass) 如果为dyb玻璃本底水平大约是schott玻璃的10倍：19.5Hz。

47. edep_pos_r <17m