Direct detection of WIMP
李金
IHEP/THU
2010.12.13 workshop in ITP
1. Principle of detection
2，New results
3，Detection technique
4，Summary
Property of WIMP
Suppose :
Element particle
• stable, came from BB
• massive
• neutral
• speed very low
• weak interaction ?
WIMP mass :
flux:
WIMP
10~100 GeV（or smaller)
100,000/cm2/s
Detection of dark matter
WIMP nuclear elastic scattering
WIMP
예상되는 사건 수
< 1/kg/day
Cs
I
Recoil nuclear
Detector / Target
recoil nuclear is normal particle , can be detected
核反冲事例率和能谱
Ge is better
Ar is better
Comparison of different dark matter target( WIMP 100GeV in mass 10e6pb
incross section) : Form factor for Ar,Xe, and Ge;
Differential rate
Integral rate over threshold
两种测量方法
本底来源电子反冲和中子的核反冲
WIMP
Gamma/betta
Interaction difference between WIMP and gamma or electron but similar to
neutron
Big challenges
Very low energy thresholds(<10 KeV) (“Quenching effect” ~1/10)
Very low event rate (cross section σ < 10-45)
Long exposures (long term stability)
Big detector (large mass,100kg 1000kg …)
Stringent background control( Cosmogenic ,Radioactive, neutrons )
Underground & Shielding (passive , active , deep site, cleanness)
Discrimination signal/background power
Measurement has to be in underground
Passive shielding & Active shielding
Neutrino background
Passive shielding & Active shielding
Passive shielding
PE, PE(B) - neutron
Lead –gamma
Cu- gamma
Ar gas –radon
Active veto
本底来源-天然放射性（α,γ, n）
核素
含量
226
Ra
1.8±0.2 Bq/Kg
（145.8 ppb）
232
Th
< 0.27 Bq/Kg
（<66.42 ppb）
锦屏地下岩石放射性含量
40
K
< 1.1Bq/Kg
（<35.53
ppm）
Background from Radon
222Rn长期平衡下，222Rn
衰变一次平均放出0.0269个光子
探测器空间中吹氮气减少氡的影响
中韩合作Y2L地下实验室KIMS实验屏蔽体和VETO
.中子屏蔽/μ子探测
铅
聚乙烯
高纯
无氧铜
LS
30cm
宇宙线Veto
中子屏蔽体
屏蔽外部等
Pb 15cm : 30t
屏蔽外部材料的本底
OFHC Cu 10cm : 3t
TEXONO实验
。
屏蔽体从外到内：
 5cm厚塑料闪烁体反符合；
 15cm厚铅室，
 25cm厚含硼聚乙烯，
 5cm厚无氧铜，
 紧贴高纯锗探测器外部的约5cm厚
的高纯CsI晶体反符合探测器
Direct detection techniques
WIMP
Ionization
10% energy
ZEPLIN II/III/Max,
XENON, LUX,
WARP, ArDM
Target
CDMS II,
EDELWEISS II
Phonons/heat
100%
energy
slowest
cryogenics
Light
DAMA/LIBRA
KIMS
ZEPLIN-I,
DEAP, CLEAN,
XMASS
1% energy
fastest
no surface
effects
CRESST II
WIMP
Ephonons
Picasso, Simple,
Coupp
(superheated)
Elight
HPGe expts
TEXONO
CDMS II,
EDELWEISS I
Eionization
Detector Techniques - Present Focus : Nuclear Vs Electron recoils
Ephonons
 Future : Lower Threshold ; Direction Sensitive
New physics results
CDMS Dec09 Results
Plus, of course, many theory papers to explain a
positive result which was not claimed ……
Calibration with Sources
Y:Number of standard deviation from the mean recoil yield
X: time relative to acceptance region
Official
Conclusion:
Spin-Independent Cross-Section
How Probable is it to Detect N>=2 events at Mean=0.8 ??
 ~19% from Poisson Distribution i.e.Very Likely to be
Statistical Effects
 ~ 1.3s in Gaussian Equivalence
CoGｅNT collaboration
２０１０．２．２５
1, 采用PC Ge 探测器
2，2100m.w.e的地下
3，采用去除本底新技术
4，3KeV附近有去不掉的多余事例
5，有可能是CDMS，并在DAMA/LIBRA的区域内
1，做了效率修正，Cut后的低能能谱，有宇宙线的峰，
Zn，Ge的EC峰
2. 点线： 触发效率，
虚线： 触发 + PSD cut效率，
实线: trigger + PSD + rise time Cut
4, 电子学脉冲标定
5，7GeV/c 和10GeV/c 的WIMP的信号（ｓｉｇｍａ＝
10e-4Pb）
1 ＤＡＭＡ，ＣｏＧｅＮＴ２００８，２０１０的结果
２，不同理论模型的预言
３，紫的区域支持ＣＤＭＳ
４，新结果偏向ＷＩＭＰ 质量在７－11GeV/C2，而不是本底
５，axioelectric dark matter 的耦合系数（０.５－８.５ＫｅＶ)
XENON100
Comments&discussion on the
results from Xenon 100
最新实验结果
高质量区
低质量区
Large mass
Convenience
Simple
PSD
Backgound
Scintillation Crystal Detector
WIMP nucleus fluorescence light
wimp
晶体