Transcript 8.55*10 -6 ppm K

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
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
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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
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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
4
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:
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•
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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
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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
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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]
A DECAY E=4.198 MeV br=79.0174%
Gamma E=0.04955 MeV br=100%
Th-234 level=0 keV[0]
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Optical parameters && Geometry
 Optical parameters
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•
Based on DYB (tuned to data), except QE
and absorption length
maxQE
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LS absorption length
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From 25m -> 40m
LS attenuation length
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•
Acrylic tank：F35.4m
Stainless Steel tank ：F38.4m
from 25% -> 35%
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
F=0.8m, G=0.7m
F
LS
Stainless
Steel
Buffer
G
Water
A=17.7m, B=1.05m, C=0.45m
A+B=18.75m (position of PMT sphere center)
B+C=1.5m,
A
B
C
D
E
Radius of PMT: 0.254m
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Detector design options
DetSim1
有机玻璃罐方案
LS/spherical acrylic vessel/water/
steel truss
DetSim2:
模块方案
LS/acrylic module/steel tank
Triangle module or single PMT module
LAB inside modules,
With LS in the gap between modules
DetSim3:
气球方案
LS/balloon/steel tank
buffer: mineral oil
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Geometry
DetSim1 && DetSim3 &&
DetSim2(single PMT module)
PMT sphere center: @18.75m
Total: 16720 PMTs
Coverage: ~76.7% 。
DetSim2 (Triangle Module)
PMT sphere center: @18.75m
Total: 17520 PMTs
Coverage: ~77%
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Compare between different detector options
 (1)Radioactivity background event rate
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From PMT glass
From LS
From Acrylic
From balloon
From dust on balloon
From steel
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14 radioactive decays in the chain
10 radioactive decays in the chain
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Generator BG event rate from PMT glass
(estimated with Schott glass)
238U
232Th
K
22 ppb
20 ppb
30 ppm
Radioactivity per PMT
22/81*10=2.716 Bq
20/246*10=0.813 Bq
30/32.3*10=9.288 Bq
12.817 Bq
Event rates per PMT
2.716*14 =38.02 Hz
0.813*10=8.13 Hz
9.288 Hz
55.438 Hz
Event rates for all PMTs
(DetSim2_Triangle module)
38.02*17520=
0.66611 MHz
8.13*17520=
0.142437MHz
9.288*17520=
0.162725MHz
0.971273MHz
Event rates for all PMTs
(DetSim1, DetSim3,
DetSim2_single PMT module)
38.02*16720=
0.635694MHz
8.13*16720=
0.135933MHz
9.288*16720=
0.155295MHz
0.926922MHz
total
55.438*17520=
55.438*16720=
Mass of glass per PMT = 10kg
238U
&& 232Th generator:
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
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模块方案 vs 气球方案 vs 有机玻璃罐方案
F=80cm
F
238U
G
background from PMT glass
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本底事例率随屏蔽层厚度的变化
(~0.5MeV)
F
G
F=30/60/80cm
(238U+232Th+40K Background from PMT glass)
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Background from acrylic
Acrylic(12cm)
DetSim1
1 ppb 238U
1 ppb
232Th
1 ppb 40K
(8.55*10-6 ppm K)
Event rates
9.60*102
2.241*102
1.499*103
Cut 600p.e.
2.39 %
4.844%
3.64%
Event rates (Hz)
22.94
10.85
54.6
Acrylic
DetSim2(single-PMTmodule)
1 ppb 238U
1 ppb 232Th
1 ppb 40K
(8.55*10-6 ppm K)
Event rates
49.725
11.602
77.630
Cut 600p.e.
3.116%
5.11%
5.77%
Event rates (Hz)
1.549431
0.593453
4.4839088
Acrylic
DetSim2(single-PMTmodule+balloon)
1 ppb 238U
1 ppb 232Th
1 ppb 40K
(8.55*10-6 ppm K)
Event rates
49.725
11.602
77.63
Cut 600p.e.
0.692%
1.424%
0.992%
Event rates (Hz)
0.344097
0.16521
0.770089
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Background from stainless steel
Steel (2cm)
DetSim1
1 ppb 238U
1 ppb 232Th
1 ppb 40K
(8.55*10-6 ppm K)
Event rates
1.317*105
3.0735*104
2.056*105
Cut 600p.e.
0%
0.00258%
0.002%
Event rates (Hz)
0
0.792
4.112
Steel (4cm)
DetSim2(single-PMTmodule)
1 ppb 238U
1 ppb 232Th
1 ppb 40K
(8.55*10-6 ppm K)
Event rates
2.638*105
6.155*104
4.118*105
Cut 600p.e.
0.0506%
0.1510%
0.089%
Event rates (Hz)
133.64
92.94
366.502
Steel (4cm)
DetSim2(single-PMTmodule_balloon)
1 ppb 238U
1 ppb 232Th
1 ppb 40K
(8.55*10-6 ppm K)
Event rates
2.621*105
6.115*104
4.092*105
Cut 600p.e.
0.00333%
0.00725%
0.005%
Event rates (Hz)
8.73
4.43
20.46
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Background from dust/balloon/LS
Background from dust on balloon surface
Background from balloon
LS
10-6ppb 238U
10-6ppb 232Th
10-6ppb 40K
(8.55*10-6 ppm K)
Event rates (Hz)
3.38
0.79
5.29
Cut 600p.e.
73.22%
73.14%
66.72%
Event rates (Hz)
2.474
0.577
3.529
238U
232Th
40K
note
Acrylic (ppt)
2
4
1
SNO Doc.
Steel (ppb)
2
3
0.2
DYB Doc.
Balloon (ppt)
2
5
6
KamLand-zen Doc.
Dust (ppm)
10-100
10-100
10-100
mass of dust depends on the class
of clean room and exposure time
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Summary of single rates (0.8m buffer)
PMT coverage
有机玻璃罐方
案
模块方案
(单PMT模块)
模块方案
(三角形模块)
气球方案
(0.8m buffer)
16720-17520 PMTs
76.7%
76.7%
77%
76.7%
PMT
(depends on glass)
100Hz~1kHz*
10kHz~100kHz
1kHz~10kHz
300Hz~3kHz**
Acrylic
~140Hz
~10Hz
~10Hz
<1Hz
LS @(10-6ppb)
(U238/Th232 /K40)
<10Hz
<10Hz
<10Hz
<10Hz
Dust on balloon
(100ppm 238U/232Th/40K)
/
/
/
~15Hz
@ 1g dust
Stainless steel tank
~3Hz (2cm)
~600Hz (4cm)
<600Hz (4cm)
~5Hz (2cm)
[email protected]
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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
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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
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Compare between different detector options
(2)Energy resolution
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
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有机玻璃罐方案的能量重建
 Strategy
I: total charge corrected with calibration curve
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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
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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
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气球方案的能量分辨率
 LS+Oil:
using IBD events, applying 17m vertex cut,
and correcting the non-linearity
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Charge Likelihood shows better performance than total PE
有机玻璃罐方案的能量分辨率
 LS+Water:
Total Charge/Charge Likelihood (Strategy III)
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有机玻璃罐方案 vs 气球方案
 Total
Charge: comparison between LS+Oil and LS+Water
For total charge, there is little difference in energy resolution for LS+water
and LS+Oil
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有机玻璃罐方案 vs 气球方案
 Charge
Likelihood: comparison between LS+Oil and
LS+Water (with 17m cut)
For charge likelihood method, the performance of LS+Oil is slightly better
than LS+Water
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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
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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
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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
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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
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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
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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。
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New
PMT个数18306个
覆盖率77.65%
Acrylic tank：F35.4m
Stainless Steel tank ：F39.9m
LS
Buffer
A
B
PMT前端屏蔽层厚度：
1.4~1.5m
C
SST
Water
D
E
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
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光学参数
发射谱
吸收重发射几率
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
吸收长度
瑞利散射长度
量子效率
折射率
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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
加或不加PMT保护罩的TotalPE分布
气球方案
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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
Momentum (GeV)
SLC5 (dyb64q)
SLC6 (sl64testq)
100
103m46.233s
74m34.637s
200
107m43.313s
77m59.391s
500
132m41.646s
97m16.513s
750
118m48.800s
86m10.328s
1000
128m9.347s
90m32.673s
2000
186m36.539s
134m45.131s
Generate Mu- at (0, 0, 20m)
Momentum = (0, 0, -P)
• 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
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Data Structure for muon events
Only save firstHitTime and nPE (Merge the hits
in a time window)
Memory Usage: < 1GB
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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
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THANKS
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
F
G
238U+232Th+40K
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Triangle Modules
5/21 PMT
5/26 PMT
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5/17 PMT
5/21 PMT
Triangle Modules
0/28 PMT
5/21 PMT
5/26 PMT
5/26 PMT
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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.
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Event rate (Schott Glass)
ALL PMT
U (MHz)
Th (MHz)
K (MHz)
Total
22 ppb
20 ppb
30 ppm
Event rates
38.02*18306=
0.695994
8.13*18306=
0.148827
9.288*18306=
0.170026
55.438*18306=
1.014848(MHz)
Cut 600 PE
0
0.0004%
0.0008%
~
Event rates
0
5.9*10-7
1.36*10-6
1.95Hz
如果为dyb玻璃本底水平大约是schott玻璃的10倍：19.5Hz。
20 kton LS
10-6ppb U238
10-6ppb Th232
10-6ppb K40
(8.55*10-6 ppm K)
Event rates
3.5 Hz
0.81 Hz
5.4 Hz
Cut 600 PE
70.66%
69.73%
62.64%
Event rates
2.47 Hz
0.56 Hz
3.38 Hz
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edep_pos_r <17m
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